Distributed Multihead X design
Kevin E. Martin
David H. Dawes
Rickard E. Faith
29 June 2004 (created 25 July 2001)
This document covers the motivation, background, design, and
implementation of the distributed multihead X (DMX) system. It
is a living document and describes the current design and
implementation details of the DMX system. As the project
progresses, this document will be continually updated to
reflect the changes in the code and/or design. Copyright 2001
by VA Linux Systems, Inc., Fremont, California. Copyright
2001-2004 by Red Hat, Inc., Raleigh, North Carolina
__________________________________________________________
Table of Contents
Introduction
The Distributed Multihead X Server
Layout of Paper
Development plan
Bootstrap code
Input device handling
Output device handling
Optimizing DMX
DMX X extension support
Common X extension support
OpenGL support
Current issues
Fonts
Zero width rendering primitives
Output scaling
Per-screen colormaps
A. Appendix
Background
Core input device handling
Output handling
Xinerama
Development Results
Phase I
Phase II
Phase III
Phase IV
Introduction
The Distributed Multihead X Server
Current Open Source multihead solutions are limited to a single
physical machine. A single X server controls multiple display
devices, which can be arranged as independent heads or unified
into a single desktop (with Xinerama). These solutions are
limited to the number of physical devices that can co-exist in
a single machine (e.g., due to the number of AGP/PCI slots
available for graphics cards). Thus, large tiled displays are
not currently possible. The work described in this paper will
eliminate the requirement that the display devices reside in
the same physical machine. This will be accomplished by
developing a front-end proxy X server that will control
multiple back-end X servers that make up the large display.
The overall structure of the distributed multihead X (DMX)
project is as follows: A single front-end X server will act as
a proxy to a set of back-end X servers, which handle all of the
visible rendering. X clients will connect to the front-end
server just as they normally would to a regular X server. The
front-end server will present an abstracted view to the client
of a single large display. This will ensure that all standard X
clients will continue to operate without modification (limited,
as always, by the visuals and extensions provided by the X
server). Clients that are DMX-aware will be able to use an
extension to obtain information about the back-end servers
(e.g., for placement of pop-up windows, window alignments by
the window manager, etc.).
The architecture of the DMX server is divided into two main
sections: input (e.g., mouse and keyboard events) and output
(e.g., rendering and windowing requests). Each of these are
describe briefly below, and the rest of this design document
will describe them in greater detail.
The DMX server can receive input from three general types of
input devices: "local" devices that are physically attached to
the machine on which DMX is running, "backend" devices that are
physically attached to one or more of the back-end X servers
(and that generate events via the X protocol stream from the
backend), and "console" devices that can be abstracted from any
non-back-end X server. Backend and console devices are treated
differently because the pointer device on the back-end X server
also controls the location of the hardware X cursor. Full
support for XInput extension devices is provided.
Rendering requests will be accepted by the front-end server;
however, rendering to visible windows will be broken down as
needed and sent to the appropriate back-end server(s) via X11
library calls for actual rendering. The basic framework will
follow a Xnest-style approach. GC state will be managed in the
front-end server and sent to the appropriate back-end server(s)
as required. Pixmap rendering will (at least initially) be
handled by the front-end X server. Windowing requests (e.g.,
ordering, mapping, moving, etc.) will handled in the front-end
server. If the request requires a visible change, the windowing
operation will be translated into requests for the appropriate
back-end server(s). Window state will be mirrored in the
back-end server(s) as needed.
Layout of Paper
The next section describes the general development plan that
was actually used for implementation. The final section
discusses outstanding issues at the conclusion of development.
The first appendix provides low-level technical detail that may
be of interest to those intimately familiar with the X server
architecture. The final appendix describes the four phases of
development that were performed during the first two years of
development.
The final year of work was divided into 9 tasks that are not
described in specific sections of this document. The major
tasks during that time were the enhancement of the
reconfiguration ability added in Phase IV, addition of support
for a dynamic number of back-end displays (instead of a
hard-coded limit), and the support for back-end display and
input removal and addition. This work is mentioned in this
paper, but is not covered in detail.
Development plan
This section describes the development plan from approximately
June 2001 through July 2003.
Bootstrap code
To allow for rapid development of the DMX server by multiple
developers during the first development stage, the problem will
be broken down into three tasks: the overall DMX framework,
back-end rendering services and input device handling services.
However, before the work begins on these tasks, a simple
framework that each developer could use was implemented to
bootstrap the development effort. This framework renders to a
single back-end server and provides dummy input devices (i.e.,
the keyboard and mouse). The simple back-end rendering service
was implemented using the shadow framebuffer support currently
available in the XFree86 environment.
Using this bootstrapping framework, each developer has been
able to work on each of the tasks listed above independently as
follows: the framework will be extended to handle arbitrary
back-end server configurations; the back-end rendering services
will be transitioned to the more efficient Xnest-style
implementation; and, an input device framework to handle
various input devices via the input extension will be
developed.
Status: The boot strap code is complete.
Input device handling
An X server (including the front-end X server) requires two
core input devices -- a keyboard and a pointer (mouse). These
core devices are handled and required by the core X11 protocol.
Additional types of input devices may be attached and utilized
via the XInput extension. These are usually referred to as
``XInput extension devices'',
There are some options as to how the front-end X server gets
its core input devices:
1. Local Input. The physical input devices (e.g., keyboard and
mouse) can be attached directly to the front-end X server.
In this case, the keyboard and mouse on the machine running
the front-end X server will be used. The front-end will
have drivers to read the raw input from those devices and
convert it into the required X input events (e.g., key
press/release, pointer button press/release, pointer
motion). The front-end keyboard driver will keep track of
keyboard properties such as key and modifier mappings,
autorepeat state, keyboard sound and led state. Similarly
the front-end pointer driver will keep track if pointer
properties such as the button mapping and movement
acceleration parameters. With this option, input is handled
fully in the front-end X server, and the back-end X servers
are used in a display-only mode. This option was
implemented and works for a limited number of
Linux-specific devices. Adding additional local input
devices for other architectures is expected to be
relatively simple.
The following options are available for implementing local
input devices:
a. The XFree86 X server has modular input drivers that
could be adapted for this purpose. The mouse driver
supports a wide range of mouse types and interfaces,
as well as a range of Operating System platforms. The
keyboard driver in XFree86 is not currently as modular
as the mouse driver, but could be made so. The XFree86
X server also has a range of other input drivers for
extended input devices such as tablets and touch
screens. Unfortunately, the XFree86 drivers are
generally complex, often simultaneously providing
support for multiple devices across multiple
architectures; and rely so heavily on XFree86-specific
helper-functions, that this option was not pursued.
b. The kdrive X server in XFree86 has built-in drivers
that support PS/2 mice and keyboard under Linux. The
mouse driver can indirectly handle other mouse types
if the Linux utility gpm is used as to translate the
native mouse protocol into PS/2 mouse format. These
drivers could be adapted and built in to the front-end
X server if this range of hardware and OS support is
sufficient. While much simpler than the XFree86
drivers, the kdrive drivers were not used for the DMX
implementation.
c. Reimplementation of keyboard and mouse drivers from
scratch for the DMX framework. Because keyboard and
mouse drivers are relatively trivial to implement,
this pathway was selected. Other drivers in the X
source tree were referenced, and significant
contributions from other drivers are noted in the DMX
source code.
2. Backend Input. The front-end can make use of the core input
devices attached to one or more of the back-end X servers.
Core input events from multiple back-ends are merged into a
single input event stream. This can work sanely when only a
single set of input devices is used at any given time. The
keyboard and pointer state will be handled in the
front-end, with changes propagated to the back-end servers
as needed. This option was implemented and works well.
Because the core pointer on a back-end controls the
hardware mouse on that back-end, core pointers cannot be
treated as XInput extension devices. However, all back-end
XInput extensions devices can be mapped to either DMX core
or DMX XInput extension devices.
3. Console Input. The front-end server could create a console
window that is displayed on an X server independent of the
back-end X servers. This console window could display
things like the physical screen layout, and the front-end
could get its core input events from events delivered to
the console window. This option was implemented and works
well. To help the human navigate, window outlines are also
displayed in the console window. Further, console windows
can be used as either core or XInput extension devices.
4. Other options were initially explored, but they were all
partial subsets of the options listed above and, hence, are
irrelevant.
Although extended input devices are not specifically mentioned
in the Distributed X requirements, the options above were all
implemented so that XInput extension devices were supported.
The bootstrap code (Xdmx) had dummy input devices, and these
are still supported in the final version. These do the
necessary initialization to satisfy the X server's requirements
for core pointer and keyboard devices, but no input events are
ever generated.
Status: The input code is complete. Because of the complexity
of the XFree86 input device drivers (and their heavy reliance
on XFree86 infrastructure), separate low-level device drivers
were implemented for Xdmx. The following kinds of drivers are
supported (in general, the devices can be treated arbitrarily
as "core" input devices or as XInput "extension" devices; and
multiple instances of different kinds of devices can be
simultaneously available):
1. A "dummy" device drive that never generates events.
2. "Local" input is from the low-level hardware on which the
Xdmx binary is running. This is the only area where using
the XFree86 driver infrastructure would have been helpful,
and then only partially, since good support for generic USB
devices does not yet exist in XFree86 (in any case, XFree86
and kdrive driver code was used where possible). Currently,
the following local devices are supported under Linux
(porting to other operating systems should be fairly
straightforward):
+ Linux keyboard
+ Linux serial mouse (MS)
+ Linux PS/2 mouse
+ USB keyboard
+ USB mouse
+ USB generic device (e.g., joystick, gamepad, etc.)
3. "Backend" input is taken from one or more of the back-end
displays. In this case, events are taken from the back-end
X server and are converted to Xdmx events. Care must be
taken so that the sprite moves properly on the display from
which input is being taken.
4. "Console" input is taken from an X window that Xdmx creates
on the operator's display (i.e., on the machine running the
Xdmx binary). When the operator's mouse is inside the
console window, then those events are converted to Xdmx
events. Several special features are available: the console
can display outlines of windows that are on the Xdmx
display (to facilitate navigation), the cursor can be
confined to the console, and a "fine" mode can be activated
to allow very precise cursor positioning.
Output device handling
The output of the DMX system displays rendering and windowing
requests across multiple screens. The screens are typically
arranged in a grid such that together they represent a single
large display.
The output section of the DMX code consists of two parts. The
first is in the front-end proxy X server (Xdmx), which accepts
client connections, manages the windows, and potentially
renders primitives but does not actually display any of the
drawing primitives. The second part is the back-end X
server(s), which accept commands from the front-end server and
display the results on their screens.
Initialization
The DMX front-end must first initialize its screens by
connecting to each of the back-end X servers and collecting
information about each of these screens. However, the
information collected from the back-end X servers might be
inconsistent. Handling these cases can be difficult and/or
inefficient. For example, a two screen system has one back-end
X server running at 16bpp while the second is running at 32bpp.
Converting rendering requests (e.g., XPutImage() or XGetImage()
requests) to the appropriate bit depth can be very time
consuming. Analyzing these cases to determine how or even if it
is possible to handle them is required. The current Xinerama
code handles many of these cases (e.g., in
PanoramiXConsolidate()) and will be used as a starting point.
In general, the best solution is to use homogeneous X servers
and display devices. Using back-end servers with the same depth
is a requirement of the final DMX implementation.
Once this screen consolidation is finished, the relative
position of each back-end X server's screen in the unified
screen is initialized. A full-screen window is opened on each
of the back-end X servers, and the cursor on each screen is
turned off. The final DMX implementation can also make use of a
partial-screen window, or multiple windows per back-end screen.
Handling rendering requests
After initialization, X applications connect to the front-end
server. There are two possible implementations of how rendering
and windowing requests are handled in the DMX system:
1. A shadow framebuffer is used in the front-end server as the
render target. In this option, all protocol requests are
completely handled in the front-end server. All state and
resources are maintained in the front-end including a
shadow copy of the entire framebuffer. The framebuffers
attached to the back-end servers are updated by XPutImage()
calls with data taken directly from the shadow framebuffer.
This solution suffers from two main problems. First, it
does not take advantage of any accelerated hardware
available in the system. Second, the size of the
XPutImage() calls can be quite large and thus will be
limited by the bandwidth available.
The initial DMX implementation used a shadow framebuffer by
default.
2. Rendering requests are sent to each back-end server for
handling (as is done in the Xnest server described above).
In this option, certain protocol requests are handled in
the front-end server and certain requests are repackaged
and then sent to the back-end servers. The framebuffer is
distributed across the multiple back-end servers. Rendering
to the framebuffer is handled on each back-end and can take
advantage of any acceleration available on the back-end
servers' graphics display device. State is maintained both
in the front and back-end servers.
This solution suffers from two main drawbacks. First,
protocol requests are sent to all back-end servers -- even
those that will completely clip the rendering primitive --
which wastes bandwidth and processing time. Second, state
is maintained both in the front- and back-end servers.
These drawbacks are not as severe as in option 1 (above)
and can either be overcome through optimizations or are
acceptable. Therefore, this option will be used in the
final implementation.
The final DMX implementation defaults to this mechanism,
but also supports the shadow framebuffer mechanism. Several
optimizations were implemented to eliminate the drawbacks
of the default mechanism. These optimizations are described
the section below and in Phase II of the Development
Results (see appendix).
Status: Both the shadow framebuffer and Xnest-style code is
complete.
Optimizing DMX
Initially, the Xnest-style solution's performance will be
measured and analyzed to determine where the performance
bottlenecks exist. There are four main areas that will be
addressed.
First, to obtain reasonable interactivity with the first
development phase, XSync() was called after each protocol
request. The XSync() function flushes any pending protocol
requests. It then waits for the back-end to process the request
and send a reply that the request has completed. This happens
with each back-end server and performance greatly suffers. As a
result of the way XSync() is called in the first development
phase, the batching that the X11 library performs is
effectively defeated. The XSync() call usage will be analyzed
and optimized by batching calls and performing them at regular
intervals, except where interactivity will suffer (e.g., on
cursor movements).
Second, the initial Xnest-style solution described above sends
the repackaged protocol requests to all back-end servers
regardless of whether or not they would be completely clipped
out. The requests that are trivially rejected on the back-end
server wastes the limited bandwidth available. By tracking
clipping changes in the DMX X server's windowing code (e.g., by
opening, closing, moving or resizing windows), we can determine
whether or not back-end windows are visible so that trivial
tests in the front-end server's GC ops drawing functions can
eliminate these unnecessary protocol requests.
Third, each protocol request will be analyzed to determine if
it is possible to break the request into smaller pieces at
display boundaries. The initial ones to be analyzed are put and
get image requests since they will require the greatest
bandwidth to transmit data between the front and back-end
servers. Other protocol requests will be analyzed and those
that will benefit from breaking them into smaller requests will
be implemented.
Fourth, an extension is being considered that will allow font
glyphs to be transferred from the front-end DMX X server to
each back-end server. This extension will permit the front-end
to handle all font requests and eliminate the requirement that
all back-end X servers share the exact same fonts as the
front-end server. We are investigating the feasibility of this
extension during this development phase.
Other potential optimizations will be determined from the
performance analysis.
Please note that in our initial design, we proposed optimizing
BLT operations (e.g., XCopyArea() and window moves) by
developing an extension that would allow individual back-end
servers to directly copy pixel data to other back-end servers.
This potential optimization was in response to the simple image
movement implementation that required potentially many calls to
GetImage() and PutImage(). However, the current Xinerama
implementation handles these BLT operations differently.
Instead of copying data to and from screens, they generate
expose events -- just as happens in the case when a window is
moved from off a screen to on screen. This approach saves the
limited bandwidth available between front and back-end servers
and is being standardized with Xinerama. It also eliminates the
potential setup problems and security issues resulting from
having each back-end server open connections to all other
back-end servers. Therefore, we suggest accepting Xinerama's
expose event solution.
Also note that the approach proposed in the second and third
optimizations might cause backing store algorithms in the
back-end to be defeated, so a DMX X server configuration flag
will be added to disable these optimizations.
Status: The optimizations proposed above are complete. It was
determined that the using the xfs font server was sufficient
and creating a new mechanism to pass glyphs was redundant;
therefore, the fourth optimization proposed above was not
included in DMX.
DMX X extension support
The DMX X server keeps track of all the windowing information
on the back-end X servers, but does not currently export this
information to any client applications. An extension will be
developed to pass the screen information and back-end window
IDs to DMX-aware clients. These clients can then use this
information to directly connect to and render to the back-end
windows. Bypassing the DMX X server allows DMX-aware clients to
break up complex rendering requests on their own and send them
directly to the windows on the back-end server's screens. An
example of a client that can make effective use of this
extension is Chromium.
Status: The extension, as implemented, is fully documented in
"Client-to-Server DMX Extension to the X Protocol". Future
changes might be required based on feedback and other proposed
enhancements to DMX. Currently, the following facilities are
supported:
1. Screen information (clipping rectangle for each screen
relative to the virtual screen)
2. Window information (window IDs and clipping information for
each back-end window that corresponds to each DMX window)
3. Input device information (mappings from DMX device IDs to
back-end device IDs)
4. Force window creation (so that a client can override the
server-side lazy window creation optimization)
5. Reconfiguration (so that a client can request that a screen
position be changed)
6. Addition and removal of back-end servers and back-end and
console inputs.
Common X extension support
The XInput, XKeyboard and Shape extensions are commonly used
extensions to the base X11 protocol. XInput allows multiple and
non-standard input devices to be accessed simultaneously. These
input devices can be connected to either the front-end or
back-end servers. XKeyboard allows much better keyboard
mappings control. Shape adds support for arbitrarily shaped
windows and is used by various window managers. Nearly all
potential back-end X servers make these extensions available,
and support for each one will be added to the DMX system.
In addition to the extensions listed above, support for the X
Rendering extension (Render) is being developed. Render adds
digital image composition to the rendering model used by the X
Window System. While this extension is still under development
by Keith Packard of HP, support for the current version will be
added to the DMX system.
Support for the XTest extension was added during the first
development phase.
Status: The following extensions are supported and are
discussed in more detail in Phase IV of the Development Results
(see appendix): BIG-REQUESTS, DEC-XTRAP, DMX, DPMS,
Extended-Visual-Information, GLX, LBX, RECORD, RENDER,
SECURITY, SHAPE, SYNC, X-Resource, XC-APPGROUP, XC-MISC,
XFree86-Bigfont, XINERAMA, XInputExtension, XKEYBOARD, and
XTEST.
OpenGL support
OpenGL support using the Mesa code base exists in XFree86
release 4 and later. Currently, the direct rendering
infrastructure (DRI) provides accelerated OpenGL support for
local clients and unaccelerated OpenGL support (i.e., software
rendering) is provided for non-local clients.
The single head OpenGL support in XFree86 4.x will be extended
to use the DMX system. When the front and back-end servers are
on the same physical hardware, it is possible to use the DRI to
directly render to the back-end servers. First, the existing
DRI will be extended to support multiple display heads, and
then to support the DMX system. OpenGL rendering requests will
be direct rendering to each back-end X server. The DRI will
request the screen layout (either from the existing Xinerama
extension or a DMX-specific extension). Support for
synchronized swap buffers will also be added (on hardware that
supports it). Note that a single front-end server with a single
back-end server on the same physical machine can emulate
accelerated indirect rendering.
When the front and back-end servers are on different physical
hardware or are using non-XFree86 4.x X servers, a mechanism to
render primitives across the back-end servers will be provided.
There are several options as to how this can be implemented.
1. The existing OpenGL support in each back-end server can be
used by repackaging rendering primitives and sending them
to each back-end server. This option is similar to the
unoptimized Xnest-style approach mentioned above.
Optimization of this solution is beyond the scope of this
project and is better suited to other distributed rendering
systems.
2. Rendering to a pixmap in the front-end server using the
current XFree86 4.x code, and then displaying to the
back-ends via calls to XPutImage() is another option. This
option is similar to the shadow frame buffer approach
mentioned above. It is slower and bandwidth intensive, but
has the advantage that the back-end servers are not
required to have OpenGL support.
These, and other, options will be investigated in this phase of
the work.
Work by others have made Chromium DMX-aware. Chromium will use
the DMX X protocol extension to obtain information about the
back-end servers and will render directly to those servers,
bypassing DMX.
Status: OpenGL support by the glxProxy extension was
implemented by SGI and has been integrated into the DMX code
base.
Current issues
In this sections the current issues are outlined that require
further investigation.
Fonts
The font path and glyphs need to be the same for the front-end
and each of the back-end servers. Font glyphs could be sent to
the back-end servers as necessary but this would consume a
significant amount of available bandwidth during font rendering
for clients that use many different fonts (e.g., Netscape).
Initially, the font server (xfs) will be used to provide the
fonts to both the front-end and back-end servers. Other
possibilities will be investigated during development.
Zero width rendering primitives
To allow pixmap and on-screen rendering to be pixel perfect,
all back-end servers must render zero width primitives exactly
the same as the front-end renders the primitives to pixmaps.
For those back-end servers that do not exactly match, zero
width primitives will be automatically converted to one width
primitives. This can be handled in the front-end server via the
GC state.
Output scaling
With very large tiled displays, it might be difficult to read
the information on the standard X desktop. In particular, the
cursor can be easily lost and fonts could be difficult to read.
Automatic primitive scaling might prove to be very useful. We
will investigate the possibility of scaling the cursor and
providing a set of alternate pre-scaled fonts to replace the
standard fonts that many applications use (e.g., fixed). Other
options for automatic scaling will also be investigated.
Per-screen colormaps
Each screen's default colormap in the set of back-end X servers
should be able to be adjusted via a configuration utility. This
support is would allow the back-end screens to be calibrated
via custom gamma tables. On 24-bit systems that support a
DirectColor visual, this type of correction can be
accommodated. One possible implementation would be to advertise
to X client of the DMX server a TrueColor visual while using
DirectColor visuals on the back-end servers to implement this
type of color correction. Other options will be investigated.
A. Appendix
Background
This section describes the existing Open Source architectures
that can be used to handle multiple screens and upon which this
development project is based. This section was written before
the implementation was finished, and may not reflect actual
details of the implementation. It is left for historical
interest only.
Core input device handling
The following is a description of how core input devices are
handled by an X server.
InitInput()
InitInput() is a DDX function that is called at the start of
each server generation from the X server's main() function. Its
purpose is to determine what input devices are connected to the
X server, register them with the DIX and MI layers, and
initialize the input event queue. InitInput() does not have a
return value, but the X server will abort if either a core
keyboard device or a core pointer device are not registered.
Extended input (XInput) devices can also be registered in
InitInput().
InitInput() usually has implementation specific code to
determine which input devices are available. For each input
device it will be using, it calls AddInputDevice():
AddInputDevice()
This DIX function allocates the device structure, registers a
callback function (which handles device init, close, on and
off), and returns the input handle, which can be treated as
opaque. It is called once for each input device.
Once input handles for core keyboard and core pointer devices
have been obtained from AddInputDevice(). If both core devices
are not registered, then the X server will exit with a fatal
error when it attempts to start the input devices in
InitAndStartDevices(), which is called directly after
InitInput() (see below).
The core pointer device is then registered with the miPointer
code (which does the high level cursor handling). While this
registration is not necessary for correct miPointer operation
in the current XFree86 code, it is still done mostly for
compatibility reasons.
miRegisterPointerDevice()
This MI function registers the core pointer's input handle with
with the miPointer code.
The final part of InitInput() is the initialization of the
input event queue handling. In most cases, the event queue
handling provided in the MI layer is used. The primary XFree86
X server uses its own event queue handling to support some
special cases related to the XInput extension and the
XFree86-specific DGA extension. For our purposes, the MI event
queue handling should be suitable. It is initialized by calling
mieqInit():
mieqInit()
This MI function initializes the MI event queue for the core
devices, and is passed the public component of the input
handles for the two core devices.
If a wakeup handler is required to deliver synchronous input
events, it can be registered here by calling the DIX function
RegisterBlockAndWakeupHandlers(). (See the devReadInput()
description below.)
InitAndStartDevices()
InitAndStartDevices() is a DIX function that is called
immediately after InitInput() from the X server's main()
function. Its purpose is to initialize each input device that
was registered with AddInputDevice(), enable each input device
that was successfully initialized, and create the list of
enabled input devices. Once each registered device is processed
in this way, the list of enabled input devices is checked to
make sure that both a core keyboard device and core pointer
device were registered and successfully enabled. If not,
InitAndStartDevices() returns failure, and results in the the X
server exiting with a fatal error.
Each registered device is initialized by calling its callback
(dev->deviceProc) with the DEVICE_INIT argument:
(*dev->deviceProc)(dev, DEVICE_INIT)
This function initializes the device structs with core
information relevant to the device.
For pointer devices, this means specifying the number of
buttons, default button mapping, the function used to get
motion events (usually miPointerGetMotionEvents()), the
function used to change/control the core pointer motion
parameters (acceleration and threshold), and the motion buffer
size.
For keyboard devices, this means specifying the keycode range,
default keycode to keysym mapping, default modifier mapping,
and the functions used to sound the keyboard bell and
modify/control the keyboard parameters (LEDs, bell pitch and
duration, key click, which keys are auto-repeating, etc).
Each initialized device is enabled by calling EnableDevice():
EnableDevice()
EnableDevice() calls the device callback with DEVICE_ON:
(*dev->deviceProc)(dev, DEVICE_ON)
This typically opens and initializes the relevant physical
device, and when appropriate, registers the device's file
descriptor (or equivalent) as a valid input source.
EnableDevice() then adds the device handle to the X server's
global list of enabled devices.
InitAndStartDevices() then verifies that a valid core keyboard
and pointer has been initialized and enabled. It returns
failure if either are missing.
devReadInput()
Each device will have some function that gets called to read
its physical input. These may be called in a number of
different ways. In the case of synchronous I/O, they will be
called from a DDX wakeup-handler that gets called after the
server detects that new input is available. In the case of
asynchronous I/O, they will be called from a (SIGIO) signal
handler triggered when new input is available. This function
should do at least two things: make sure that input events get
enqueued, and make sure that the cursor gets moved for motion
events (except if these are handled later by the driver's own
event queue processing function, which cannot be done when
using the MI event queue handling).
Events are queued by calling mieqEnqueue():
mieqEnqueue()
This MI function is used to add input events to the event
queue. It is simply passed the event to be queued.
The cursor position should be updated when motion events are
enqueued, by calling either miPointerAbsoluteCursor() or
miPointerDeltaCursor():
miPointerAbsoluteCursor()
This MI function is used to move the cursor to the absolute
coordinates provided.
miPointerDeltaCursor()
This MI function is used to move the cursor relative to its
current position.
ProcessInputEvents()
ProcessInputEvents() is a DDX function that is called from the
X server's main dispatch loop when new events are available in
the input event queue. It typically processes the enqueued
events, and updates the cursor/pointer position. It may also do
other DDX-specific event processing.
Enqueued events are processed by mieqProcessInputEvents() and
passed to the DIX layer for transmission to clients:
mieqProcessInputEvents()
This function processes each event in the event queue, and
passes it to the device's input processing function. The DIX
layer provides default functions to do this processing, and
they handle the task of getting the events passed back to the
relevant clients.
miPointerUpdate()
This function resynchronized the cursor position with the new
pointer position. It also takes care of moving the cursor
between screens when needed in multi-head configurations.
DisableDevice()
DisableDevice is a DIX function that removes an input device
from the list of enabled devices. The result of this is that
the device no longer generates input events. The device's data
structures are kept in place, and disabling a device like this
can be reversed by calling EnableDevice(). DisableDevice() may
be called from the DDX when it is desirable to do so (e.g., the
XFree86 server does this when VT switching). Except for special
cases, this is not normally called for core input devices.
DisableDevice() calls the device's callback function with
DEVICE_OFF:
(*dev->deviceProc)(dev, DEVICE_OFF)
This typically closes the relevant physical device, and when
appropriate, unregisters the device's file descriptor (or
equivalent) as a valid input source.
DisableDevice() then removes the device handle from the X
server's global list of enabled devices.
CloseDevice()
CloseDevice is a DIX function that removes an input device from
the list of available devices. It disables input from the
device and frees all data structures associated with the
device. This function is usually called from
CloseDownDevices(), which is called from main() at the end of
each server generation to close all input devices.
CloseDevice() calls the device's callback function with
DEVICE_CLOSE:
(*dev->deviceProc)(dev, DEVICE_CLOSE)
This typically closes the relevant physical device, and when
appropriate, unregisters the device's file descriptor (or
equivalent) as a valid input source. If any device specific
data structures were allocated when the device was initialized,
they are freed here.
CloseDevice() then frees the data structures that were
allocated for the device when it was registered/initialized.
LegalModifier()
LegalModifier() is a required DDX function that can be used to
restrict which keys may be modifier keys. This seems to be
present for historical reasons, so this function should simply
return TRUE unconditionally.
Output handling
The following sections describe the main functions required to
initialize, use and close the output device(s) for each screen
in the X server.
InitOutput()
This DDX function is called near the start of each server
generation from the X server's main() function. InitOutput()'s
main purpose is to initialize each screen and fill in the
global screenInfo structure for each screen. It is passed three
arguments: a pointer to the screenInfo struct, which it is to
initialize, and argc and argv from main(), which can be used to
determine additional configuration information.
The primary tasks for this function are outlined below:
1. Parse configuration info: The first task of InitOutput() is
to parses any configuration information from the
configuration file. In addition to the XF86Config file,
other configuration information can be taken from the
command line. The command line options can be gathered
either in InitOutput() or earlier in the
ddxProcessArgument() function, which is called by
ProcessCommandLine(). The configuration information
determines the characteristics of the screen(s). For
example, in the XFree86 X server, the XF86Config file
specifies the monitor information, the screen resolution,
the graphics devices and slots in which they are located,
and, for Xinerama, the screens' layout.
2. Initialize screen info: The next task is to initialize the
screen-dependent internal data structures. For example,
part of what the XFree86 X server does is to allocate its
screen and pixmap private indices, probe for graphics
devices, compare the probed devices to the ones listed in
the XF86Config file, and add the ones that match to the
internal xf86Screens[] structure.
3. Set pixmap formats: The next task is to initialize the
screenInfo's image byte order, bitmap bit order and bitmap
scanline unit/pad. The screenInfo's pixmap format's depth,
bits per pixel and scanline padding is also initialized at
this stage.
4. Unify screen info: An optional task that might be done at
this stage is to compare all of the information from the
various screens and determines if they are compatible
(i.e., if the set of screens can be unified into a single
desktop). This task has potential to be useful to the DMX
front-end server, if Xinerama's PanoramiXConsolidate()
function is not sufficient.
Once these tasks are complete, the valid screens are known and
each of these screens can be initialized by calling
AddScreen().
AddScreen()
This DIX function is called from InitOutput(), in the DDX
layer, to add each new screen to the screenInfo structure. The
DDX screen initialization function and command line arguments
(i.e., argc and argv) are passed to it as arguments.
This function first allocates a new Screen structure and any
privates that are required. It then initializes some of the
fields in the Screen struct and sets up the pixmap padding
information. Finally, it calls the DDX screen initialization
function ScreenInit(), which is described below. It returns the
number of the screen that were just added, or -1 if there is
insufficient memory to add the screen or if the DDX screen
initialization fails.
ScreenInit()
This DDX function initializes the rest of the Screen structure
with either generic or screen-specific functions (as
necessary). It also fills in various screen attributes (e.g.,
width and height in millimeters, black and white pixel values).
The screen init function usually calls several functions to
perform certain screen initialization functions. They are
described below:
{mi,*fb}ScreenInit()
The DDX layer's ScreenInit() function usually calls another
layer's ScreenInit() function (e.g., miScreenInit() or
fbScreenInit()) to initialize the fallbacks that the DDX driver
does not specifically handle.
After calling another layer's ScreenInit() function, any
screen-specific functions either wrap or replace the other
layer's function pointers. If a function is to be wrapped, each
of the old function pointers from the other layer are stored in
a screen private area. Common functions to wrap are
CloseScreen() and SaveScreen().
miInitializeBackingStore()
This MI function initializes the screen's backing storage
functions, which are used to save areas of windows that are
currently covered by other windows.
miDCInitialize()
This MI function initializes the MI cursor display structures
and function pointers. If a hardware cursor is used, the DDX
layer's ScreenInit() function will wrap additional screen and
the MI cursor display function pointers.
Another common task for ScreenInit() function is to initialize
the output device state. For example, in the XFree86 X server,
the ScreenInit() function saves the original state of the video
card and then initializes the video mode of the graphics
device.
CloseScreen()
This function restores any wrapped screen functions (and in
particular the wrapped CloseScreen() function) and restores the
state of the output device to its original state. It should
also free any private data it created during the screen
initialization.
GC operations
When the X server is requested to render drawing primitives, it
does so by calling drawing functions through the graphics
context's operation function pointer table (i.e., the GCOps
functions). These functions render the basic graphics
operations such as drawing rectangles, lines, text or copying
pixmaps. Default routines are provided either by the MI layer,
which draws indirectly through a simple span interface, or by
the framebuffer layers (e.g., CFB, MFB, FB), which draw
directly to a linearly mapped frame buffer.
To take advantage of special hardware on the graphics device,
specific GCOps functions can be replaced by device specific
code. However, many times the graphics devices can handle only
a subset of the possible states of the GC, so during graphics
context validation, appropriate routines are selected based on
the state and capabilities of the hardware. For example, some
graphics hardware can accelerate single pixel width lines with
certain dash patterns. Thus, for dash patterns that are not
supported by hardware or for width 2 or greater lines, the
default routine is chosen during GC validation.
Note that some pointers to functions that draw to the screen
are stored in the Screen structure. They include GetImage(),
GetSpans(), CopyWindow() and RestoreAreas().
Xnest
The Xnest X server is a special proxy X server that relays the
X protocol requests that it receives to a ``real'' X server
that then processes the requests and displays the results, if
applicable. To the X applications, Xnest appears as if it is a
regular X server. However, Xnest is both server to the X
application and client of the real X server, which will
actually handle the requests.
The Xnest server implements all of the standard input and
output initialization steps outlined above.
InitOutput()
Xnest takes its configuration information from command line
arguments via ddxProcessArguments(). This information includes
the real X server display to connect to, its default visual
class, the screen depth, the Xnest window's geometry, etc.
Xnest then connects to the real X server and gathers visual,
colormap, depth and pixmap information about that server's
display, creates a window on that server, which will be used as
the root window for Xnest.
Next, Xnest initializes its internal data structures and uses
the data from the real X server's pixmaps to initialize its own
pixmap formats. Finally, it calls AddScreen(xnestOpenScreen,
argc, argv) to initialize each of its screens.
ScreenInit()
Xnest's ScreenInit() function is called xnestOpenScreen(). This
function initializes its screen's depth and visual information,
and then calls miScreenInit() to set up the default screen
functions. It then calls miInitializeBackingStore() and
miDCInitialize() to initialize backing store and the software
cursor. Finally, it replaces many of the screen functions with
its own functions that repackage and send the requests to the
real X server to which Xnest is attached.
CloseScreen()
This function frees its internal data structure allocations.
Since it replaces instead of wrapping screen functions, there
are no function pointers to unwrap. This can potentially lead
to problems during server regeneration.
GC operations
The GC operations in Xnest are very simple since they leave all
of the drawing to the real X server to which Xnest is attached.
Each of the GCOps takes the request and sends it to the real X
server using standard Xlib calls. For example, the X
application issues a XDrawLines() call. This function turns
into a protocol request to Xnest, which calls the
xnestPolylines() function through Xnest's GCOps function
pointer table. The xnestPolylines() function is only a single
line, which calls XDrawLines() using the same arguments that
were passed into it. Other GCOps functions are very similar.
Two exceptions to the simple GCOps functions described above
are the image functions and the BLT operations.
The image functions, GetImage() and PutImage(), must use a
temporary image to hold the image to be put of the image that
was just grabbed from the screen while it is in transit to the
real X server or the client. When the image has been
transmitted, the temporary image is destroyed.
The BLT operations, CopyArea() and CopyPlane(), handle not only
the copy function, which is the same as the simple cases
described above, but also the graphics exposures that result
when the GC's graphics exposure bit is set to True. Graphics
exposures are handled in a helper function,
xnestBitBlitHelper(). This function collects the exposure
events from the real X server and, if any resulting in regions
being exposed, then those regions are passed back to the MI
layer so that it can generate exposure events for the X
application.
The Xnest server takes its input from the X server to which it
is connected. When the mouse is in the Xnest server's window,
keyboard and mouse events are received by the Xnest server,
repackaged and sent back to any client that requests those
events.
Shadow framebuffer
The most common type of framebuffer is a linear array memory
that maps to the video memory on the graphics device. However,
accessing that video memory over an I/O bus (e.g., ISA or PCI)
can be slow. The shadow framebuffer layer allows the developer
to keep the entire framebuffer in main memory and copy it back
to video memory at regular intervals. It also has been extended
to handle planar video memory and rotated framebuffers.
There are two main entry points to the shadow framebuffer code:
shadowAlloc(width, height, bpp)
This function allocates the in memory copy of the framebuffer
of size width*height*bpp. It returns a pointer to that memory,
which will be used by the framebuffer ScreenInit() code during
the screen's initialization.
shadowInit(pScreen, updateProc, windowProc)
This function initializes the shadow framebuffer layer. It
wraps several screen drawing functions, and registers a block
handler that will update the screen. The updateProc is a
function that will copy the damaged regions to the screen, and
the windowProc is a function that is used when the entire
linear video memory range cannot be accessed simultaneously so
that only a window into that memory is available (e.g., when
using the VGA aperture).
The shadow framebuffer code keeps track of the damaged area of
each screen by calculating the bounding box of all drawing
operations that have occurred since the last screen update.
Then, when the block handler is next called, only the damaged
portion of the screen is updated.
Note that since the shadow framebuffer is kept in main memory,
all drawing operations are performed by the CPU and, thus, no
accelerated hardware drawing operations are possible.
Xinerama
Xinerama is an X extension that allows multiple physical
screens controlled by a single X server to appear as a single
screen. Although the extension allows clients to find the
physical screen layout via extension requests, it is completely
transparent to clients at the core X11 protocol level. The
original public implementation of Xinerama came from
Digital/Compaq. XFree86 rewrote it, filling in some missing
pieces and improving both X11 core protocol compliance and
performance. The Xinerama extension will be passing through
X.Org's standardization process in the near future, and the
sample implementation will be based on this rewritten version.
The current implementation of Xinerama is based primarily in
the DIX (device independent) and MI (machine independent)
layers of the X server. With few exceptions the DDX layers do
not need any changes to support Xinerama. X server extensions
often do need modifications to provide full Xinerama
functionality.
The following is a code-level description of how Xinerama
functions.
Note: Because the Xinerama extension was originally called the
PanoramiX extension, many of the Xinerama functions still have
the PanoramiX prefix.
PanoramiXExtensionInit()
PanoramiXExtensionInit() is a device-independent extension
function that is called at the start of each server generation
from InitExtensions(), which is called from the X server's
main() function after all output devices have been initialized,
but before any input devices have been initialized.
PanoramiXNumScreens is set to the number of physical screens.
If only one physical screen is present, the extension is
disabled, and PanoramiXExtensionInit() returns without doing
anything else.
The Xinerama extension is registered by calling AddExtension().
GC and Screen private indexes are allocated, and both GC and
Screen private areas are allocated for each physical screen.
These hold Xinerama-specific per-GC and per-Screen data. Each
screen's CreateGC and CloseScreen functions are wrapped by
XineramaCreateGC() and XineramaCloseScreen() respectively. Some
new resource classes are created for Xinerama drawables and
GCs, and resource types for Xinerama windows, pixmaps and
colormaps.
A region (PanoramiXScreenRegion) is initialized to be the union
of the screen regions. The relative positioning information for
the physical screens is taken from the ScreenRec x and y
members, which the DDX layer must initialize in InitOutput().
The bounds of the combined screen is also calculated
(PanoramiXPixWidth and PanoramiXPixHeight).
The DIX layer has a list of function pointers (ProcVector[])
that holds the entry points for the functions that process core
protocol requests. The requests that Xinerama must intercept
and break up into physical screen-specific requests are
wrapped. The original set is copied to SavedProcVector[]. The
types of requests intercepted are Window requests, GC requests,
colormap requests, drawing requests, and some geometry-related
requests. This wrapping allows the bulk of the protocol request
processing to be handled transparently to the DIX layer. Some
operations cannot be dealt with in this way and are handled
with Xinerama-specific code within the DIX layer.
PanoramiXConsolidate()
PanoramiXConsolidate() is a device-independent extension
function that is called directly from the X server's main()
function after extensions and input/output devices have been
initialized, and before the root windows are defined and
initialized.
This function finds the set of depths (PanoramiXDepths[]) and
visuals (PanoramiXVisuals[]) common to all of the physical
screens. PanoramiXNumDepths is set to the number of common
depths, and PanoramiXNumVisuals is set to the number of common
visuals. Resources are created for the single root window and
the default colormap. Each of these resources has per-physical
screen entries.
PanoramiXCreateConnectionBlock()
PanoramiXConsolidate() is a device-independent extension
function that is called directly from the X server's main()
function after the per-physical screen root windows are
created. It is called instead of the standard DIX
CreateConnectionBlock() function. If this function returns
FALSE, the X server exits with a fatal error. This function
will return FALSE if no common depths were found in
PanoramiXConsolidate(). With no common depths, Xinerama mode is
not possible.
The connection block holds the information that clients get
when they open a connection to the X server. It includes
information such as the supported pixmap formats, number of
screens and the sizes, depths, visuals, default colormap
information, etc, for each of the screens (much of information
that xdpyinfo shows). The connection block is initialized with
the combined single screen values that were calculated in the
above two functions.
The Xinerama extension allows the registration of connection
block callback functions. The purpose of these is to allow
other extensions to do processing at this point. These
callbacks can be registered by calling
XineramaRegisterConnectionBlockCallback() from the other
extension's ExtensionInit() function. Each registered
connection block callback is called at the end of
PanoramiXCreateConnectionBlock().
Xinerama-specific changes to the DIX code
There are a few types of Xinerama-specific changes within the
DIX code. The main ones are described here.
Functions that deal with colormap or GC -related operations
outside of the intercepted protocol requests have a test added
to only do the processing for screen numbers > 0. This is
because they are handled for the single Xinerama screen and the
processing is done once for screen 0.
The handling of motion events does some coordinate translation
between the physical screen's origin and screen zero's origin.
Also, motion events must be reported relative to the composite
screen origin rather than the physical screen origins.
There is some special handling for cursor, window and event
processing that cannot (either not at all or not conveniently)
be done via the intercepted protocol requests. A particular
case is the handling of pointers moving between physical
screens.
Xinerama-specific changes to the MI code
The only Xinerama-specific change to the MI code is in
miSendExposures() to handle the coordinate (and window ID)
translation for expose events.
Intercepted DIX core requests
Xinerama breaks up drawing requests for dispatch to each
physical screen. It also breaks up windows into pieces for each
physical screen. GCs are translated into per-screen GCs.
Colormaps are replicated on each physical screen. The functions
handling the intercepted requests take care of breaking the
requests and repackaging them so that they can be passed to the
standard request handling functions for each screen in turn. In
addition, and to aid the repackaging, the information from many
of the intercepted requests is used to keep up to date the
necessary state information for the single composite screen.
Requests (usually those with replies) that can be satisfied
completely from this stored state information do not call the
standard request handling functions.
Development Results
In this section the results of each phase of development are
discussed. This development took place between approximately
June 2001 and July 2003.
Phase I
The initial development phase dealt with the basic
implementation including the bootstrap code, which used the
shadow framebuffer, and the unoptimized implementation, based
on an Xnest-style implementation.
Scope
The goal of Phase I is to provide fundamental functionality
that can act as a foundation for ongoing work:
1. Develop the proxy X server
+ The proxy X server will operate on the X11 protocol
and relay requests as necessary to correctly perform
the request.
+ Work will be based on the existing work for Xinerama
and Xnest.
+ Input events and windowing operations are handled in
the proxy server and rendering requests are repackaged
and sent to each of the back-end servers for display.
+ The multiple screen layout (including support for
overlapping screens) will be user configurable via a
configuration file or through the configuration tool.
2. Develop graphical configuration tool
+ There will be potentially a large number of X servers
to configure into a single display. The tool will
allow the user to specify which servers are involved
in the configuration and how they should be laid out.
3. Pass the X Test Suite
+ The X Test Suite covers the basic X11 operations. All
tests known to succeed must correctly operate in the
distributed X environment.
For this phase, the back-end X servers are assumed to be
unmodified X servers that do not support any DMX-related
protocol extensions; future optimization pathways are
considered, but are not implemented; and the configuration tool
is assumed to rely only on libraries in the X source tree
(e.g., Xt).
Results
The proxy X server, Xdmx, was developed to distribute X11
protocol requests to the set of back-end X servers. It opens a
window on each back-end server, which represents the part of
the front-end's root window that is visible on that screen. It
mirrors window, pixmap and other state in each back-end server.
Drawing requests are sent to either windows or pixmaps on each
back-end server. This code is based on Xnest and uses the
existing Xinerama extension.
Input events can be taken from (1) devices attached to the
back-end server, (2) core devices attached directly to the Xdmx
server, or (3) from a ``console'' window on another X server.
Events for these devices are gathered, processed and delivered
to clients attached to the Xdmx server.
An intuitive configuration format was developed to help the
user easily configure the multiple back-end X servers. It was
defined (see grammar in Xdmx man page) and a parser was
implemented that is used by the Xdmx server and by a standalone
xdmxconfig utility. The parsing support was implemented such
that it can be easily factored out of the X source tree for use
with other tools (e.g., vdl). Support for converting legacy
vdl-format configuration files to the DMX format is provided by
the vdltodmx utility.
Originally, the configuration file was going to be a subsection
of XFree86's XF86Config file, but that was not possible since
Xdmx is a completely separate X server. Thus, a separate config
file format was developed. In addition, a graphical
configuration tool, xdmxconfig, was developed to allow the user
to create and arrange the screens in the configuration file.
The -configfile and -config command-line options can be used to
start Xdmx using a configuration file.
An extension that enables remote input testing is required for
the X Test Suite to function. During this phase, this extension
(XTEST) was implemented in the Xdmx server. The results from
running the X Test Suite are described in detail below.
X Test Suite
Introduction
The X Test Suite contains tests that verify Xlib functions
operate correctly. The test suite is designed to run on a
single X server; however, since X applications will not be able
to tell the difference between the DMX server and a standard X
server, the X Test Suite should also run on the DMX server.
The Xdmx server was tested with the X Test Suite, and the
existing failures are noted in this section. To put these
results in perspective, we first discuss expected X Test
failures and how errors in underlying systems can impact Xdmx
test results.
Expected Failures for a Single Head
A correctly implemented X server with a single screen is
expected to fail certain X Test tests. The following well-known
errors occur because of rounding error in the X server code:
XDrawArc: Tests 42, 63, 66, 73
XDrawArcs: Tests 45, 66, 69, 76
The following failures occur because of the high-level X server
implementation:
XLoadQueryFont: Test 1
XListFontsWithInfo: Tests 3, 4
XQueryFont: Tests 1, 2
The following test fails when running the X server as root
under Linux because of the way directory modes are interpreted:
XWriteBitmapFile: Test 3
Depending on the video card used for the back-end, other
failures may also occur because of bugs in the low-level driver
implementation. Over time, failures of this kind are usually
fixed by XFree86, but will show up in Xdmx testing until then.
Expected Failures for Xinerama
Xinerama fails several X Test Suite tests because of design
decisions made for the current implementation of Xinerama. Over
time, many of these errors will be corrected by XFree86 and the
group working on a new Xinerama implementation. Therefore, Xdmx
will also share X Suite Test failures with Xinerama.
We may be able to fix or work-around some of these failures at
the Xdmx level, but this will require additional exploration
that was not part of Phase I.
Xinerama is constantly improving, and the list of
Xinerama-related failures depends on XFree86 version and the
underlying graphics hardware. We tested with a variety of
hardware, including nVidia, S3, ATI Radeon, and Matrox G400 (in
dual-head mode). The list below includes only those failures
that appear to be from the Xinerama layer, and does not include
failures listed in the previous section, or failures that
appear to be from the low-level graphics driver itself:
These failures were noted with multiple Xinerama
configurations:
XCopyPlane: Tests 13, 22, 31 (well-known Xinerama implementatio
n issue)
XSetFontPath: Test 4
XGetDefault: Test 5
XMatchVisualInfo: Test 1
These failures were noted only when using one dual-head video
card with a 4.2.99.x XFree86 server:
XListPixmapFormats: Test 1
XDrawRectangles: Test 45
These failures were noted only when using two video cards from
different vendors with a 4.1.99.x XFree86 server:
XChangeWindowAttributes: Test 32
XCreateWindow: Test 30
XDrawLine: Test 22
XFillArc: Test 22
XChangeKeyboardControl: Tests 9, 10
XRebindKeysym: Test 1
Additional Failures from Xdmx
When running Xdmx, no unexpected failures were noted. Since the
Xdmx server is based on Xinerama, we expect to have most of the
Xinerama failures present in the Xdmx server. Similarly, since
the Xdmx server must rely on the low-level device drivers on
each back-end server, we also expect that Xdmx will exhibit
most of the back-end failures. Here is a summary:
XListPixmapFormats: Test 1 (configuration dependent)
XChangeWindowAttributes: Test 32
XCreateWindow: Test 30
XCopyPlane: Test 13, 22, 31
XSetFontPath: Test 4
XGetDefault: Test 5 (configuration dependent)
XMatchVisualInfo: Test 1
XRebindKeysym: Test 1 (configuration dependent)
Note that this list is shorter than the combined list for
Xinerama because Xdmx uses different code paths to perform some
Xinerama operations. Further, some Xinerama failures have been
fixed in the XFree86 4.2.99.x CVS repository.
Summary and Future Work
Running the X Test Suite on Xdmx does not produce any failures
that cannot be accounted for by the underlying Xinerama
subsystem used by the front-end or by the low-level
device-driver code running on the back-end X servers. The Xdmx
server therefore is as ``correct'' as possible with respect to
the standard set of X Test Suite tests.
During the following phases, we will continue to verify Xdmx
correctness using the X Test Suite. We may also use other tests
suites or write additional tests that run under the X Test
Suite that specifically verify the expected behavior of DMX.
Fonts
In Phase I, fonts are handled directly by both the front-end
and the back-end servers, which is required since we must treat
each back-end server during this phase as a ``black box''. What
this requires is that the front- and back-end servers must
share the exact same font path. There are two ways to help make
sure that all servers share the same font path:
1. First, each server can be configured to use the same font
server. The font server, xfs, can be configured to serve
fonts to multiple X servers via TCP.
2. Second, each server can be configured to use the same font
path and either those font paths can be copied to each
back-end machine or they can be mounted (e.g., via NFS) on
each back-end machine.
One additional concern is that a client program can set its own
font path, and if it does so, then that font path must be
available on each back-end machine.
The -fontpath command line option was added to allow users to
initialize the font path of the front end server. This font
path is propagated to each back-end server when the default
font is loaded. If there are any problems, an error message is
printed, which will describe the problem and list the current
font path. For more information about setting the font path,
see the -fontpath option description in the man page.
Performance
Phase I of development was not intended to optimize
performance. Its focus was on completely and correctly handling
the base X11 protocol in the Xdmx server. However, several
insights were gained during Phase I, which are listed here for
reference during the next phase of development.
1. Calls to XSync() can slow down rendering since it requires
a complete round trip to and from a back-end server. This
is especially problematic when communicating over long haul
networks.
2. Sending drawing requests to only the screens that they
overlap should improve performance.
Pixmaps
Pixmaps were originally expected to be handled entirely in the
front-end X server; however, it was found that this overly
complicated the rendering code and would have required sending
potentially large images to each back server that required them
when copying from pixmap to screen. Thus, pixmap state is
mirrored in the back-end server just as it is with regular
window state. With this implementation, the same rendering code
that draws to windows can be used to draw to pixmaps on the
back-end server, and no large image transfers are required to
copy from pixmap to window.
Phase II
The second phase of development concentrates on performance
optimizations. These optimizations are documented here, with
x11perf data to show how the optimizations improve performance.
All benchmarks were performed by running Xdmx on a dual
processor 1.4GHz AMD Athlon machine with 1GB of RAM connecting
over 100baseT to two single-processor 1GHz Pentium III machines
with 256MB of RAM and ATI Rage 128 (RF) video cards. The front
end was running Linux 2.4.20-pre1-ac1 and the back ends were
running Linux 2.4.7-10 and version 4.2.99.1 of XFree86 pulled
from the XFree86 CVS repository on August 7, 2002. All systems
were running Red Hat Linux 7.2.
Moving from XFree86 4.1.99.1 to 4.2.0.0
For phase II, the working source tree was moved to the branch
tagged with dmx-1-0-branch and was updated from version
4.1.99.1 (20 August 2001) of the XFree86 sources to version
4.2.0.0 (18 January 2002). After this update, the following
tests were noted to be more than 10% faster:
1.13 Fill 300x300 opaque stippled trapezoid (161x145 stipple)
1.16 Fill 1x1 tiled trapezoid (161x145 tile)
1.13 Fill 10x10 tiled trapezoid (161x145 tile)
1.17 Fill 100x100 tiled trapezoid (161x145 tile)
1.16 Fill 1x1 tiled trapezoid (216x208 tile)
1.20 Fill 10x10 tiled trapezoid (216x208 tile)
1.15 Fill 100x100 tiled trapezoid (216x208 tile)
1.37 Circulate Unmapped window (200 kids)
And the following tests were noted to be more than 10% slower:
0.88 Unmap window via parent (25 kids)
0.75 Circulate Unmapped window (4 kids)
0.79 Circulate Unmapped window (16 kids)
0.80 Circulate Unmapped window (25 kids)
0.82 Circulate Unmapped window (50 kids)
0.85 Circulate Unmapped window (75 kids)
These changes were not caused by any changes in the DMX system,
and may point to changes in the XFree86 tree or to tests that
have more "jitter" than most other x11perf tests.
Global changes
During the development of the Phase II DMX server, several
global changes were made. These changes were also compared with
the Phase I server. The following tests were noted to be more
than 10% faster:
1.13 Fill 300x300 opaque stippled trapezoid (161x145 stipple)
1.15 Fill 1x1 tiled trapezoid (161x145 tile)
1.13 Fill 10x10 tiled trapezoid (161x145 tile)
1.17 Fill 100x100 tiled trapezoid (161x145 tile)
1.16 Fill 1x1 tiled trapezoid (216x208 tile)
1.19 Fill 10x10 tiled trapezoid (216x208 tile)
1.15 Fill 100x100 tiled trapezoid (216x208 tile)
1.15 Circulate Unmapped window (4 kids)
The following tests were noted to be more than 10% slower:
0.69 Scroll 10x10 pixels
0.68 Scroll 100x100 pixels
0.68 Copy 10x10 from window to window
0.68 Copy 100x100 from window to window
0.76 Circulate Unmapped window (75 kids)
0.83 Circulate Unmapped window (100 kids)
For the remainder of this analysis, the baseline of comparison
will be the Phase II deliverable with all optimizations
disabled (unless otherwise noted). This will highlight how the
optimizations in isolation impact performance.
XSync() Batching
During the Phase I implementation, XSync() was called after
every protocol request made by the DMX server. This provided
the DMX server with an interactive feel, but defeated X11's
protocol buffering system and introduced round-trip wire
latency into every operation. During Phase II, DMX was changed
so that protocol requests are no longer followed by calls to
XSync(). Instead, the need for an XSync() is noted, and XSync()
calls are only made every 100mS or when the DMX server
specifically needs to make a call to guarantee interactivity.
With this new system, X11 buffers protocol as much as possible
during a 100mS interval, and many unnecessary XSync() calls are
avoided.
Out of more than 300 x11perf tests, 8 tests became more than
100 times faster, with 68 more than 50X faster, 114 more than
10X faster, and 181 more than 2X faster. See table below for
summary.
The following tests were noted to be more than 10% slower with
XSync() batching on:
0.88 500x500 tiled rectangle (161x145 tile)
0.89 Copy 500x500 from window to window
Offscreen Optimization
Windows span one or more of the back-end servers' screens;
however, during Phase I development, windows were created on
every back-end server and every rendering request was sent to
every window regardless of whether or not that window was
visible. With the offscreen optimization, the DMX server tracks
when a window is completely off of a back-end server's screen
and, in that case, it does not send rendering requests to those
back-end windows. This optimization saves bandwidth between the
front and back-end servers, and it reduces the number of
XSync() calls. The performance tests were run on a DMX system
with only two back-end servers. Greater performance gains will
be had as the number of back-end servers increases.
Out of more than 300 x11perf tests, 3 tests were at least twice
as fast, and 146 tests were at least 10% faster. Two tests were
more than 10% slower with the offscreen optimization:
0.88 Hide/expose window via popup (4 kids)
0.89 Resize unmapped window (75 kids)
Lazy Window Creation Optimization
As mentioned above, during Phase I, windows were created on
every back-end server even if they were not visible on that
back-end. With the lazy window creation optimization, the DMX
server does not create windows on a back-end server until they
are either visible or they become the parents of a visible
window. This optimization builds on the offscreen optimization
(described above) and requires it to be enabled.
The lazy window creation optimization works by creating the
window data structures in the front-end server when a client
creates a window, but delays creation of the window on the
back-end server(s). A private window structure in the DMX
server saves the relevant window data and tracks changes to the
window's attributes and stacking order for later use. The only
times a window is created on a back-end server are (1) when it
is mapped and is at least partially overlapping the back-end
server's screen (tracked by the offscreen optimization), or (2)
when the window becomes the parent of a previously visible
window. The first case occurs when a window is mapped or when a
visible window is copied, moved or resized and now overlaps the
back-end server's screen. The second case occurs when starting
a window manager after having created windows to which the
window manager needs to add decorations.
When either case occurs, a window on the back-end server is
created using the data saved in the DMX server's window private
data structure. The stacking order is then adjusted to
correctly place the window on the back-end and lastly the
window is mapped. From this time forward, the window is handled
exactly as if the window had been created at the time of the
client's request.
Note that when a window is no longer visible on a back-end
server's screen (e.g., it is moved offscreen), the window is
not destroyed; rather, it is kept and reused later if the
window once again becomes visible on the back-end server's
screen. Originally with this optimization, destroying windows
was implemented but was later rejected because it increased
bandwidth when windows were opaquely moved or resized, which is
common in many window managers.
The performance tests were run on a DMX system with only two
back-end servers. Greater performance gains will be had as the
number of back-end servers increases.
This optimization improved the following x11perf tests by more
than 10%:
1.10 500x500 rectangle outline
1.12 Fill 100x100 stippled trapezoid (161x145 stipple)
1.20 Circulate Unmapped window (50 kids)
1.19 Circulate Unmapped window (75 kids)
Subdividing Rendering Primitives
X11 imaging requests transfer significant data between the
client and the X server. During Phase I, the DMX server would
then transfer the image data to each back-end server. Even with
the offscreen optimization (above), these requests still
required transferring significant data to each back-end server
that contained a visible portion of the window. For example, if
the client uses XPutImage() to copy an image to a window that
overlaps the entire DMX screen, then the entire image is copied
by the DMX server to every back-end server.
To reduce the amount of data transferred between the DMX server
and the back-end servers when XPutImage() is called, the image
data is subdivided and only the data that will be visible on a
back-end server's screen is sent to that back-end server.
Xinerama already implements a subdivision algorithm for
XGetImage() and no further optimization was needed.
Other rendering primitives were analyzed, but the time required
to subdivide these primitives was a significant proportion of
the time required to send the entire rendering request to the
back-end server, so this optimization was rejected for the
other rendering primitives.
Again, the performance tests were run on a DMX system with only
two back-end servers. Greater performance gains will be had as
the number of back-end servers increases.
This optimization improved the following x11perf tests by more
than 10%:
1.12 Fill 100x100 stippled trapezoid (161x145 stipple)
1.26 PutImage 10x10 square
1.83 PutImage 100x100 square
1.91 PutImage 500x500 square
1.40 PutImage XY 10x10 square
1.48 PutImage XY 100x100 square
1.50 PutImage XY 500x500 square
1.45 Circulate Unmapped window (75 kids)
1.74 Circulate Unmapped window (100 kids)
The following test was noted to be more than 10% slower with
this optimization:
0.88 10-pixel fill chord partial circle
Summary of x11perf Data
With all of the optimizations on, 53 x11perf tests are more
than 100X faster than the unoptimized Phase II deliverable,
with 69 more than 50X faster, 73 more than 10X faster, and 199
more than twice as fast. No tests were more than 10% slower
than the unoptimized Phase II deliverable. (Compared with the
Phase I deliverable, only Circulate Unmapped window (100 kids)
was more than 10% slower than the Phase II deliverable. As
noted above, this test seems to have wider variability than
other x11perf tests.)
The following table summarizes relative x11perf test changes
for all optimizations individually and collectively. Note that
some of the optimizations have a synergistic effect when used
together.
1: XSync() batching only
2: Off screen optimizations only
3: Window optimizations only
4: Subdivprims only
5: All optimizations
1 2 3 4 5 Operation
------ ---- ---- ---- ------ ---------
2.14 1.85 1.00 1.00 4.13 Dot
1.67 1.80 1.00 1.00 3.31 1x1 rectangle
2.38 1.43 1.00 1.00 2.44 10x10 rectangle
1.00 1.00 0.92 0.98 1.00 100x100 rectangle
1.00 1.00 1.00 1.00 1.00 500x500 rectangle
1.83 1.85 1.05 1.06 3.54 1x1 stippled rectangle (8x8 stipple)
2.43 1.43 1.00 1.00 2.41 10x10 stippled rectangle (8x8 stipple)
0.98 1.00 1.00 1.00 1.00 100x100 stippled rectangle (8x8 stipple)
1.00 1.00 1.00 1.00 0.98 500x500 stippled rectangle (8x8 stipple)
1.75 1.75 1.00 1.00 3.40 1x1 opaque stippled rectangle (8x8 stipple)
2.38 1.42 1.00 1.00 2.34 10x10 opaque stippled rectangle (8x8 stippl
e)
1.00 1.00 0.97 0.97 1.00 100x100 opaque stippled rectangle (8x8 stip
ple)
1.00 1.00 1.00 1.00 0.99 500x500 opaque stippled rectangle (8x8 stip
ple)
1.82 1.82 1.04 1.04 3.56 1x1 tiled rectangle (4x4 tile)
2.33 1.42 1.00 1.00 2.37 10x10 tiled rectangle (4x4 tile)
1.00 0.92 1.00 1.00 1.00 100x100 tiled rectangle (4x4 tile)
1.00 1.00 1.00 1.00 1.00 500x500 tiled rectangle (4x4 tile)
1.94 1.62 1.00 1.00 3.66 1x1 stippled rectangle (17x15 stipple)
1.74 1.28 1.00 1.00 1.73 10x10 stippled rectangle (17x15 stipple)
1.00 1.00 1.00 0.89 0.98 100x100 stippled rectangle (17x15 stipple)
1.00 1.00 1.00 1.00 0.98 500x500 stippled rectangle (17x15 stipple)
1.94 1.62 1.00 1.00 3.67 1x1 opaque stippled rectangle (17x15 stippl
e)
1.69 1.26 1.00 1.00 1.66 10x10 opaque stippled rectangle (17x15 stip
ple)
1.00 0.95 1.00 1.00 1.00 100x100 opaque stippled rectangle (17x15 st
ipple)
1.00 1.00 1.00 1.00 0.97 500x500 opaque stippled rectangle (17x15 st
ipple)
1.93 1.61 0.99 0.99 3.69 1x1 tiled rectangle (17x15 tile)
1.73 1.27 1.00 1.00 1.72 10x10 tiled rectangle (17x15 tile)
1.00 1.00 1.00 1.00 0.98 100x100 tiled rectangle (17x15 tile)
1.00 1.00 0.97 0.97 1.00 500x500 tiled rectangle (17x15 tile)
1.95 1.63 1.00 1.00 3.83 1x1 stippled rectangle (161x145 stipple)
1.80 1.30 1.00 1.00 1.83 10x10 stippled rectangle (161x145 stipple)
0.97 1.00 1.00 1.00 1.01 100x100 stippled rectangle (161x145 stipple
)
1.00 1.00 1.00 1.00 0.98 500x500 stippled rectangle (161x145 stipple
)
1.95 1.63 1.00 1.00 3.56 1x1 opaque stippled rectangle (161x145 stip
ple)
1.65 1.25 1.00 1.00 1.68 10x10 opaque stippled rectangle (161x145 st
ipple)
1.00 1.00 1.00 1.00 1.01 100x100 opaque stippled rectangle (161x145.
..
1.00 1.00 1.00 1.00 0.97 500x500 opaque stippled rectangle (161x145.
..
1.95 1.63 0.98 0.99 3.80 1x1 tiled rectangle (161x145 tile)
1.67 1.26 1.00 1.00 1.67 10x10 tiled rectangle (161x145 tile)
1.13 1.14 1.14 1.14 1.14 100x100 tiled rectangle (161x145 tile)
0.88 1.00 1.00 1.00 0.99 500x500 tiled rectangle (161x145 tile)
1.93 1.63 1.00 1.00 3.53 1x1 tiled rectangle (216x208 tile)
1.69 1.26 1.00 1.00 1.66 10x10 tiled rectangle (216x208 tile)
1.00 1.00 1.00 1.00 1.00 100x100 tiled rectangle (216x208 tile)
1.00 1.00 1.00 1.00 1.00 500x500 tiled rectangle (216x208 tile)
1.82 1.70 1.00 1.00 3.38 1-pixel line segment
2.07 1.56 0.90 1.00 3.31 10-pixel line segment
1.29 1.10 1.00 1.00 1.27 100-pixel line segment
1.05 1.06 1.03 1.03 1.09 500-pixel line segment
1.30 1.13 1.00 1.00 1.29 100-pixel line segment (1 kid)
1.32 1.15 1.00 1.00 1.32 100-pixel line segment (2 kids)
1.33 1.16 1.00 1.00 1.33 100-pixel line segment (3 kids)
1.92 1.64 1.00 1.00 3.73 10-pixel dashed segment
1.34 1.16 1.00 1.00 1.34 100-pixel dashed segment
1.24 1.11 0.99 0.97 1.23 100-pixel double-dashed segment
1.72 1.77 1.00 1.00 3.25 10-pixel horizontal line segment
1.83 1.66 1.01 1.00 3.54 100-pixel horizontal line segment
1.86 1.30 1.00 1.00 1.84 500-pixel horizontal line segment
2.11 1.52 1.00 0.99 3.02 10-pixel vertical line segment
1.21 1.10 1.00 1.00 1.20 100-pixel vertical line segment
1.03 1.03 1.00 1.00 1.02 500-pixel vertical line segment
4.42 1.68 1.00 1.01 4.64 10x1 wide horizontal line segment
1.83 1.31 1.00 1.00 1.83 100x10 wide horizontal line segment
1.07 1.00 0.96 1.00 1.07 500x50 wide horizontal line segment
4.10 1.67 1.00 1.00 4.62 10x1 wide vertical line segment
1.50 1.24 1.06 1.06 1.48 100x10 wide vertical line segment
1.06 1.03 1.00 1.00 1.05 500x50 wide vertical line segment
2.54 1.61 1.00 1.00 3.61 1-pixel line
2.71 1.48 1.00 1.00 2.67 10-pixel line
1.19 1.09 1.00 1.00 1.19 100-pixel line
1.04 1.02 1.00 1.00 1.03 500-pixel line
2.68 1.51 0.98 1.00 3.17 10-pixel dashed line
1.23 1.11 0.99 0.99 1.23 100-pixel dashed line
1.15 1.08 1.00 1.00 1.15 100-pixel double-dashed line
2.27 1.39 1.00 1.00 2.23 10x1 wide line
1.20 1.09 1.00 1.00 1.20 100x10 wide line
1.04 1.02 1.00 1.00 1.04 500x50 wide line
1.52 1.45 1.00 1.00 1.52 100x10 wide dashed line
1.54 1.47 1.00 1.00 1.54 100x10 wide double-dashed line
1.97 1.30 0.96 0.95 1.95 10x10 rectangle outline
1.44 1.27 1.00 1.00 1.43 100x100 rectangle outline
3.22 2.16 1.10 1.09 3.61 500x500 rectangle outline
1.95 1.34 1.00 1.00 1.90 10x10 wide rectangle outline
1.14 1.14 1.00 1.00 1.13 100x100 wide rectangle outline
1.00 1.00 1.00 1.00 1.00 500x500 wide rectangle outline
1.57 1.72 1.00 1.00 3.03 1-pixel circle
1.96 1.35 1.00 1.00 1.92 10-pixel circle
1.21 1.07 0.86 0.97 1.20 100-pixel circle
1.08 1.04 1.00 1.00 1.08 500-pixel circle
1.39 1.19 1.03 1.03 1.38 100-pixel dashed circle
1.21 1.11 1.00 1.00 1.23 100-pixel double-dashed circle
1.59 1.28 1.00 1.00 1.58 10-pixel wide circle
1.22 1.12 0.99 1.00 1.22 100-pixel wide circle
1.06 1.04 1.00 1.00 1.05 500-pixel wide circle
1.87 1.84 1.00 1.00 1.85 100-pixel wide dashed circle
1.90 1.93 1.01 1.01 1.90 100-pixel wide double-dashed circle
2.13 1.43 1.00 1.00 2.32 10-pixel partial circle
1.42 1.18 1.00 1.00 1.42 100-pixel partial circle
1.92 1.85 1.01 1.01 1.89 10-pixel wide partial circle
1.73 1.67 1.00 1.00 1.73 100-pixel wide partial circle
1.36 1.95 1.00 1.00 2.64 1-pixel solid circle
2.02 1.37 1.00 1.00 2.03 10-pixel solid circle
1.19 1.09 1.00 1.00 1.19 100-pixel solid circle
1.02 0.99 1.00 1.00 1.01 500-pixel solid circle
1.74 1.28 1.00 0.88 1.73 10-pixel fill chord partial circle
1.31 1.13 1.00 1.00 1.31 100-pixel fill chord partial circle
1.67 1.31 1.03 1.03 1.72 10-pixel fill slice partial circle
1.30 1.13 1.00 1.00 1.28 100-pixel fill slice partial circle
2.45 1.49 1.01 1.00 2.71 10-pixel ellipse
1.22 1.10 1.00 1.00 1.22 100-pixel ellipse
1.09 1.04 1.00 1.00 1.09 500-pixel ellipse
1.90 1.28 1.00 1.00 1.89 100-pixel dashed ellipse
1.62 1.24 0.96 0.97 1.61 100-pixel double-dashed ellipse
2.43 1.50 1.00 1.00 2.42 10-pixel wide ellipse
1.61 1.28 1.03 1.03 1.60 100-pixel wide ellipse
1.08 1.05 1.00 1.00 1.08 500-pixel wide ellipse
1.93 1.88 1.00 1.00 1.88 100-pixel wide dashed ellipse
1.94 1.89 1.01 1.00 1.94 100-pixel wide double-dashed ellipse
2.31 1.48 1.00 1.00 2.67 10-pixel partial ellipse
1.38 1.17 1.00 1.00 1.38 100-pixel partial ellipse
2.00 1.85 0.98 0.97 1.98 10-pixel wide partial ellipse
1.89 1.86 1.00 1.00 1.89 100-pixel wide partial ellipse
3.49 1.60 1.00 1.00 3.65 10-pixel filled ellipse
1.67 1.26 1.00 1.00 1.67 100-pixel filled ellipse
1.06 1.04 1.00 1.00 1.06 500-pixel filled ellipse
2.38 1.43 1.01 1.00 2.32 10-pixel fill chord partial ellipse
2.06 1.30 1.00 1.00 2.05 100-pixel fill chord partial ellipse
2.27 1.41 1.00 1.00 2.27 10-pixel fill slice partial ellipse
1.98 1.33 1.00 0.97 1.97 100-pixel fill slice partial ellipse
57.46 1.99 1.01 1.00 114.92 Fill 1x1 equivalent triangle
56.94 1.98 1.01 1.00 73.89 Fill 10x10 equivalent triangle
6.07 1.75 1.00 1.00 6.07 Fill 100x100 equivalent triangle
51.12 1.98 1.00 1.00 102.81 Fill 1x1 trapezoid
51.42 1.82 1.01 1.00 94.89 Fill 10x10 trapezoid
6.47 1.80 1.00 1.00 6.44 Fill 100x100 trapezoid
1.56 1.28 1.00 0.99 1.56 Fill 300x300 trapezoid
51.27 1.97 0.96 0.97 102.54 Fill 1x1 stippled trapezoid (8x8 stipple)
51.73 2.00 1.02 1.02 67.92 Fill 10x10 stippled trapezoid (8x8 stipple)
5.36 1.72 1.00 1.00 5.36 Fill 100x100 stippled trapezoid (8x8 stippl
e)
1.54 1.26 1.00 1.00 1.59 Fill 300x300 stippled trapezoid (8x8 stippl
e)
51.41 1.94 1.01 1.00 102.82 Fill 1x1 opaque stippled trapezoid (8x8 sti
pple)
50.71 1.95 0.99 1.00 65.44 Fill 10x10 opaque stippled trapezoid (8x8..
.
5.33 1.73 1.00 1.00 5.36 Fill 100x100 opaque stippled trapezoid (8x8
...
1.58 1.25 1.00 1.00 1.58 Fill 300x300 opaque stippled trapezoid (8x8
...
51.56 1.96 0.99 0.90 103.68 Fill 1x1 tiled trapezoid (4x4 tile)
51.59 1.99 1.01 1.01 62.25 Fill 10x10 tiled trapezoid (4x4 tile)
5.38 1.72 1.00 1.00 5.38 Fill 100x100 tiled trapezoid (4x4 tile)
1.54 1.25 1.00 0.99 1.58 Fill 300x300 tiled trapezoid (4x4 tile)
51.70 1.98 1.01 1.01 103.98 Fill 1x1 stippled trapezoid (17x15 stipple)
44.86 1.97 1.00 1.00 44.86 Fill 10x10 stippled trapezoid (17x15 stippl
e)
2.74 1.56 1.00 1.00 2.73 Fill 100x100 stippled trapezoid (17x15 stip
ple)
1.29 1.14 1.00 1.00 1.27 Fill 300x300 stippled trapezoid (17x15 stip
ple)
51.41 1.96 0.96 0.95 103.39 Fill 1x1 opaque stippled trapezoid (17x15..
.
45.14 1.96 1.01 1.00 45.14 Fill 10x10 opaque stippled trapezoid (17x15
...
2.68 1.56 1.00 1.00 2.68 Fill 100x100 opaque stippled trapezoid (17x
15...
1.26 1.10 1.00 1.00 1.28 Fill 300x300 opaque stippled trapezoid (17x
15...
51.13 1.97 1.00 0.99 103.39 Fill 1x1 tiled trapezoid (17x15 tile)
47.58 1.96 1.00 1.00 47.86 Fill 10x10 tiled trapezoid (17x15 tile)
2.74 1.56 1.00 1.00 2.74 Fill 100x100 tiled trapezoid (17x15 tile)
1.29 1.14 1.00 1.00 1.28 Fill 300x300 tiled trapezoid (17x15 tile)
51.13 1.97 0.99 0.97 103.39 Fill 1x1 stippled trapezoid (161x145 stippl
e)
45.14 1.97 1.00 1.00 44.29 Fill 10x10 stippled trapezoid (161x145 stip
ple)
3.02 1.77 1.12 1.12 3.38 Fill 100x100 stippled trapezoid (161x145 st
ipple)
1.31 1.13 1.00 1.00 1.30 Fill 300x300 stippled trapezoid (161x145 st
ipple)
51.27 1.97 1.00 1.00 103.10 Fill 1x1 opaque stippled trapezoid (161x145
...
45.01 1.97 1.00 1.00 45.01 Fill 10x10 opaque stippled trapezoid (161x1
45...
2.67 1.56 1.00 1.00 2.69 Fill 100x100 opaque stippled trapezoid (161
x145..
1.29 1.13 1.00 1.01 1.27 Fill 300x300 opaque stippled trapezoid (161
x145..
51.41 1.96 1.00 0.99 103.39 Fill 1x1 tiled trapezoid (161x145 tile)
45.01 1.96 0.98 1.00 45.01 Fill 10x10 tiled trapezoid (161x145 tile)
2.62 1.36 1.00 1.00 2.69 Fill 100x100 tiled trapezoid (161x145 tile)
1.27 1.13 1.00 1.00 1.22 Fill 300x300 tiled trapezoid (161x145 tile)
51.13 1.98 1.00 1.00 103.39 Fill 1x1 tiled trapezoid (216x208 tile)
45.14 1.97 1.01 0.99 45.14 Fill 10x10 tiled trapezoid (216x208 tile)
2.62 1.55 1.00 1.00 2.71 Fill 100x100 tiled trapezoid (216x208 tile)
1.28 1.13 1.00 1.00 1.20 Fill 300x300 tiled trapezoid (216x208 tile)
50.71 1.95 1.00 1.00 54.70 Fill 10x10 equivalent complex polygon
5.51 1.71 0.96 0.98 5.47 Fill 100x100 equivalent complex polygons
8.39 1.97 1.00 1.00 16.75 Fill 10x10 64-gon (Convex)
8.38 1.83 1.00 1.00 8.43 Fill 100x100 64-gon (Convex)
8.50 1.96 1.00 1.00 16.64 Fill 10x10 64-gon (Complex)
8.26 1.83 1.00 1.00 8.35 Fill 100x100 64-gon (Complex)
14.09 1.87 1.00 1.00 14.05 Char in 80-char line (6x13)
11.91 1.87 1.00 1.00 11.95 Char in 70-char line (8x13)
11.16 1.85 1.01 1.00 11.10 Char in 60-char line (9x15)
10.09 1.78 1.00 1.00 10.09 Char16 in 40-char line (k14)
6.15 1.75 1.00 1.00 6.31 Char16 in 23-char line (k24)
11.92 1.90 1.03 1.03 11.88 Char in 80-char line (TR 10)
8.18 1.78 1.00 0.99 8.17 Char in 30-char line (TR 24)
42.83 1.44 1.01 1.00 42.11 Char in 20/40/20 line (6x13, TR 10)
27.45 1.43 1.01 1.01 27.45 Char16 in 7/14/7 line (k14, k24)
12.13 1.85 1.00 1.00 12.05 Char in 80-char image line (6x13)
10.00 1.84 1.00 1.00 10.00 Char in 70-char image line (8x13)
9.18 1.83 1.00 1.00 9.12 Char in 60-char image line (9x15)
9.66 1.82 0.98 0.95 9.66 Char16 in 40-char image line (k14)
5.82 1.72 1.00 1.00 5.99 Char16 in 23-char image line (k24)
8.70 1.80 1.00 1.00 8.65 Char in 80-char image line (TR 10)
4.67 1.66 1.00 1.00 4.67 Char in 30-char image line (TR 24)
84.43 1.47 1.00 1.00 124.18 Scroll 10x10 pixels
3.73 1.50 1.00 0.98 3.73 Scroll 100x100 pixels
1.00 1.00 1.00 1.00 1.00 Scroll 500x500 pixels
84.43 1.51 1.00 1.00 134.02 Copy 10x10 from window to window
3.62 1.51 0.98 0.98 3.62 Copy 100x100 from window to window
0.89 1.00 1.00 1.00 1.00 Copy 500x500 from window to window
57.06 1.99 1.00 1.00 88.64 Copy 10x10 from pixmap to window
2.49 2.00 1.00 1.00 2.48 Copy 100x100 from pixmap to window
1.00 0.91 1.00 1.00 0.98 Copy 500x500 from pixmap to window
2.04 1.01 1.00 1.00 2.03 Copy 10x10 from window to pixmap
1.05 1.00 1.00 1.00 1.05 Copy 100x100 from window to pixmap
1.00 1.00 0.93 1.00 1.04 Copy 500x500 from window to pixmap
58.52 1.03 1.03 1.02 57.95 Copy 10x10 from pixmap to pixmap
2.40 1.00 1.00 1.00 2.45 Copy 100x100 from pixmap to pixmap
1.00 1.00 1.00 1.00 1.00 Copy 500x500 from pixmap to pixmap
51.57 1.92 1.00 1.00 85.75 Copy 10x10 1-bit deep plane
6.37 1.75 1.01 1.01 6.37 Copy 100x100 1-bit deep plane
1.26 1.11 1.00 1.00 1.24 Copy 500x500 1-bit deep plane
4.23 1.63 0.98 0.97 4.38 Copy 10x10 n-bit deep plane
1.04 1.02 1.00 1.00 1.04 Copy 100x100 n-bit deep plane
1.00 1.00 1.00 1.00 1.00 Copy 500x500 n-bit deep plane
6.45 1.98 1.00 1.26 12.80 PutImage 10x10 square
1.10 1.87 1.00 1.83 2.11 PutImage 100x100 square
1.02 1.93 1.00 1.91 1.91 PutImage 500x500 square
4.17 1.78 1.00 1.40 7.18 PutImage XY 10x10 square
1.27 1.49 0.97 1.48 2.10 PutImage XY 100x100 square
1.00 1.50 1.00 1.50 1.52 PutImage XY 500x500 square
1.07 1.01 1.00 1.00 1.06 GetImage 10x10 square
1.01 1.00 1.00 1.00 1.01 GetImage 100x100 square
1.00 1.00 1.00 1.00 1.00 GetImage 500x500 square
1.56 1.00 0.99 0.97 1.56 GetImage XY 10x10 square
1.02 1.00 1.00 1.00 1.02 GetImage XY 100x100 square
1.00 1.00 1.00 1.00 1.00 GetImage XY 500x500 square
1.00 1.00 1.01 0.98 0.95 X protocol NoOperation
1.02 1.03 1.04 1.03 1.00 QueryPointer
1.03 1.02 1.04 1.03 1.00 GetProperty
100.41 1.51 1.00 1.00 198.76 Change graphics context
45.81 1.00 0.99 0.97 57.10 Create and map subwindows (4 kids)
78.45 1.01 1.02 1.02 63.07 Create and map subwindows (16 kids)
73.91 1.01 1.00 1.00 56.37 Create and map subwindows (25 kids)
73.22 1.00 1.00 1.00 49.07 Create and map subwindows (50 kids)
72.36 1.01 0.99 1.00 32.14 Create and map subwindows (75 kids)
70.34 1.00 1.00 1.00 30.12 Create and map subwindows (100 kids)
55.00 1.00 1.00 0.99 23.75 Create and map subwindows (200 kids)
55.30 1.01 1.00 1.00 141.03 Create unmapped window (4 kids)
55.38 1.01 1.01 1.00 163.25 Create unmapped window (16 kids)
54.75 0.96 1.00 0.99 166.95 Create unmapped window (25 kids)
54.83 1.00 1.00 0.99 178.81 Create unmapped window (50 kids)
55.38 1.01 1.01 1.00 181.20 Create unmapped window (75 kids)
55.38 1.01 1.01 1.00 181.20 Create unmapped window (100 kids)
54.87 1.01 1.01 1.00 182.05 Create unmapped window (200 kids)
28.13 1.00 1.00 1.00 30.75 Map window via parent (4 kids)
36.14 1.01 1.01 1.01 32.58 Map window via parent (16 kids)
26.13 1.00 0.98 0.95 29.85 Map window via parent (25 kids)
40.07 1.00 1.01 1.00 27.57 Map window via parent (50 kids)
23.26 0.99 1.00 1.00 18.23 Map window via parent (75 kids)
22.91 0.99 1.00 0.99 16.52 Map window via parent (100 kids)
27.79 1.00 1.00 0.99 12.50 Map window via parent (200 kids)
22.35 1.00 1.00 1.00 56.19 Unmap window via parent (4 kids)
9.57 1.00 0.99 1.00 89.78 Unmap window via parent (16 kids)
80.77 1.01 1.00 1.00 103.85 Unmap window via parent (25 kids)
96.34 1.00 1.00 1.00 116.06 Unmap window via parent (50 kids)
99.72 1.00 1.00 1.00 124.93 Unmap window via parent (75 kids)
112.36 1.00 1.00 1.00 125.27 Unmap window via parent (100 kids)
105.41 1.00 1.00 0.99 120.00 Unmap window via parent (200 kids)
51.29 1.03 1.02 1.02 74.19 Destroy window via parent (4 kids)
86.75 0.99 0.99 0.99 116.87 Destroy window via parent (16 kids)
106.43 1.01 1.01 1.01 127.49 Destroy window via parent (25 kids)
120.34 1.01 1.01 1.00 140.11 Destroy window via parent (50 kids)
126.67 1.00 0.99 0.99 145.00 Destroy window via parent (75 kids)
126.11 1.01 1.01 1.00 140.56 Destroy window via parent (100 kids)
128.57 1.01 1.00 1.00 137.91 Destroy window via parent (200 kids)
16.04 0.88 1.00 1.00 20.36 Hide/expose window via popup (4 kids)
19.04 1.01 1.00 1.00 23.48 Hide/expose window via popup (16 kids)
19.22 1.00 1.00 1.00 20.44 Hide/expose window via popup (25 kids)
17.41 1.00 0.91 0.97 17.68 Hide/expose window via popup (50 kids)
17.29 1.01 1.00 1.01 17.07 Hide/expose window via popup (75 kids)
16.74 1.00 1.00 1.00 16.17 Hide/expose window via popup (100 kids)
10.30 1.00 1.00 1.00 10.51 Hide/expose window via popup (200 kids)
16.48 1.01 1.00 1.00 26.05 Move window (4 kids)
17.01 0.95 1.00 1.00 23.97 Move window (16 kids)
16.95 1.00 1.00 1.00 22.90 Move window (25 kids)
16.05 1.01 1.00 1.00 21.32 Move window (50 kids)
15.58 1.00 0.98 0.98 19.44 Move window (75 kids)
14.98 1.02 1.03 1.03 18.17 Move window (100 kids)
10.90 1.01 1.01 1.00 12.68 Move window (200 kids)
49.42 1.00 1.00 1.00 198.27 Moved unmapped window (4 kids)
50.72 0.97 1.00 1.00 193.66 Moved unmapped window (16 kids)
50.87 1.00 0.99 1.00 195.09 Moved unmapped window (25 kids)
50.72 1.00 1.00 1.00 189.34 Moved unmapped window (50 kids)
50.87 1.00 1.00 1.00 191.33 Moved unmapped window (75 kids)
50.87 1.00 1.00 0.90 186.71 Moved unmapped window (100 kids)
50.87 1.00 1.00 1.00 179.19 Moved unmapped window (200 kids)
41.04 1.00 1.00 1.00 56.61 Move window via parent (4 kids)
69.81 1.00 1.00 1.00 130.82 Move window via parent (16 kids)
95.81 1.00 1.00 1.00 141.92 Move window via parent (25 kids)
95.98 1.00 1.00 1.00 149.43 Move window via parent (50 kids)
96.59 1.01 1.01 1.00 153.98 Move window via parent (75 kids)
97.19 1.00 1.00 1.00 157.30 Move window via parent (100 kids)
96.67 1.00 0.99 0.96 159.44 Move window via parent (200 kids)
17.75 1.01 1.00 1.00 27.61 Resize window (4 kids)
17.94 1.00 1.00 0.99 25.42 Resize window (16 kids)
17.92 1.01 1.00 1.00 24.47 Resize window (25 kids)
17.24 0.97 1.00 1.00 24.14 Resize window (50 kids)
16.81 1.00 1.00 0.99 22.75 Resize window (75 kids)
16.08 1.00 1.00 1.00 21.20 Resize window (100 kids)
12.92 1.00 0.99 1.00 16.26 Resize window (200 kids)
52.94 1.01 1.00 1.00 327.12 Resize unmapped window (4 kids)
53.60 1.01 1.01 1.01 333.71 Resize unmapped window (16 kids)
52.99 1.00 1.00 1.00 337.29 Resize unmapped window (25 kids)
51.98 1.00 1.00 1.00 329.38 Resize unmapped window (50 kids)
53.05 0.89 1.00 1.00 322.60 Resize unmapped window (75 kids)
53.05 1.00 1.00 1.00 318.08 Resize unmapped window (100 kids)
53.11 1.00 1.00 0.99 306.21 Resize unmapped window (200 kids)
16.76 1.00 0.96 1.00 19.46 Circulate window (4 kids)
17.24 1.00 1.00 0.97 16.24 Circulate window (16 kids)
16.30 1.03 1.03 1.03 15.85 Circulate window (25 kids)
13.45 1.00 1.00 1.00 14.90 Circulate window (50 kids)
12.91 1.00 1.00 1.00 13.06 Circulate window (75 kids)
11.30 0.98 1.00 1.00 11.03 Circulate window (100 kids)
7.58 1.01 1.01 0.99 7.47 Circulate window (200 kids)
1.01 1.01 0.98 1.00 0.95 Circulate Unmapped window (4 kids)
1.07 1.07 1.01 1.07 1.02 Circulate Unmapped window (16 kids)
1.04 1.09 1.06 1.05 0.97 Circulate Unmapped window (25 kids)
1.04 1.23 1.20 1.18 1.05 Circulate Unmapped window (50 kids)
1.18 1.53 1.19 1.45 1.24 Circulate Unmapped window (75 kids)
1.08 1.02 1.01 1.74 1.01 Circulate Unmapped window (100 kids)
1.01 1.12 0.98 0.91 0.97 Circulate Unmapped window (200 kids)
Profiling with OProfile
OProfile (available from http://oprofile.sourceforge.net/) is a
system-wide profiler for Linux systems that uses
processor-level counters to collect sampling data. OProfile can
provide information that is similar to that provided by gprof,
but without the necessity of recompiling the program with
special instrumentation (i.e., OProfile can collect statistical
profiling information about optimized programs). A test harness
was developed to collect OProfile data for each x11perf test
individually.
Test runs were performed using the RETIRED_INSNS counter on the
AMD Athlon and the CPU_CLK_HALTED counter on the Intel Pentium
III (with a test configuration different from the one described
above). We have examined OProfile output and have compared it
with gprof output. This investigation has not produced results
that yield performance increases in x11perf numbers.
X Test Suite
The X Test Suite was run on the fully optimized DMX server
using the configuration described above. The following failures
were noted:
XListPixmapFormats: Test 1 [1]
XChangeWindowAttributes: Test 32 [1]
XCreateWindow: Test 30 [1]
XFreeColors: Test 4 [3]
XCopyArea: Test 13, 17, 21, 25, 30 [2]
XCopyPlane: Test 11, 15, 27, 31 [2]
XSetFontPath: Test 4 [1]
XChangeKeyboardControl: Test 9, 10 [1]
[1] Previously documented errors expected from the Xinerama
implementation (see Phase I discussion).
[2] Newly noted errors that have been verified as expected
behavior of the Xinerama implementation.
[3] Newly noted error that has been verified as a Xinerama
implementation bug.
Phase III
During the third phase of development, support was provided for
the following extensions: SHAPE, RENDER, XKEYBOARD, XInput.
SHAPE
The SHAPE extension is supported. Test applications (e.g.,
xeyes and oclock) and window managers that make use of the
SHAPE extension will work as expected.
RENDER
The RENDER extension is supported. The version included in the
DMX CVS tree is version 0.2, and this version is fully
supported by Xdmx. Applications using only version 0.2
functions will work correctly; however, some apps that make use
of functions from later versions do not properly check the
extension's major/minor version numbers. These apps will fail
with a Bad Implementation error when using post-version 0.2
functions. This is expected behavior. When the DMX CVS tree is
updated to include newer versions of RENDER, support for these
newer functions will be added to the DMX X server.
XKEYBOARD
The XKEYBOARD extension is supported. If present on the
back-end X servers, the XKEYBOARD extension will be used to
obtain information about the type of the keyboard for
initialization. Otherwise, the keyboard will be initialized
using defaults. Note that this departs from older behavior:
when Xdmx is compiled without XKEYBOARD support, the map from
the back-end X server will be preserved. With XKEYBOARD
support, the map is not preserved because better information
and control of the keyboard is available.
XInput
The XInput extension is supported. Any device can be used as a
core device and be used as an XInput extension device, with the
exception of core devices on the back-end servers. This
limitation is present because cursor handling on the back-end
requires that the back-end cursor sometimes track the Xdmx core
cursor -- behavior that is incompatible with using the back-end
pointer as a non-core device.
Currently, back-end extension devices are not available as Xdmx
extension devices, but this limitation should be removed in the
future.
To demonstrate the XInput extension, and to provide more
examples for low-level input device driver writers, USB device
drivers have been written for mice (usb-mou), keyboards
(usb-kbd), and non-mouse/non-keyboard USB devices (usb-oth).
Please see the man page for information on Linux kernel drivers
that are required for using these Xdmx drivers.
DPMS
The DPMS extension is exported but does not do anything at this
time.
Other Extensions
The LBX, SECURITY, XC-APPGROUP, and XFree86-Bigfont extensions
do not require any special Xdmx support and have been exported.
The BIG-REQUESTS, DEC-XTRAP, DOUBLE-BUFFER,
Extended-Visual-Information, FontCache, GLX, MIT-SCREEN-SAVER,
MIT-SHM, MIT-SUNDRY-NONSTANDARD, RECORD, SECURITY, SGI-GLX,
SYNC, TOG-CUP, X-Resource, XC-MISC, XFree86-DGA, XFree86-DRI,
XFree86-Misc, XFree86-VidModeExtension, and XVideo extensions
are not supported at this time, but will be evaluated for
inclusion in future DMX releases. See below for additional work
on extensions after Phase III.
Phase IV
Moving to XFree86 4.3.0
For Phase IV, the recent release of XFree86 4.3.0 (27 February
2003) was merged onto the dmx.sourceforge.net CVS trunk and all
work is proceeding using this tree.
Extensions
XC-MISC (supported)
XC-MISC is used internally by the X library to recycle XIDs
from the X server. This is important for long-running X server
sessions. Xdmx supports this extension. The X Test Suite passed
and failed the exact same tests before and after this extension
was enabled.
Extended-Visual-Information (supported)
The Extended-Visual-Information extension provides a method for
an X client to obtain detailed visual information. Xdmx
supports this extension. It was tested using the
hw/dmx/examples/evi example program. Note that this extension
is not Xinerama-aware -- it will return visual information for
each screen even though Xinerama is causing the X server to
export a single logical screen.
RES (supported)
The X-Resource extension provides a mechanism for a client to
obtain detailed information about the resources used by other
clients. This extension was tested with the hw/dmx/examples/res
program. The X Test Suite passed and failed the exact same
tests before and after this extension was enabled.
BIG-REQUESTS (supported)
This extension enables the X11 protocol to handle requests
longer than 262140 bytes. The X Test Suite passed and failed
the exact same tests before and after this extension was
enabled.
XSYNC (supported)
This extension provides facilities for two different X clients
to synchronize their requests. This extension was minimally
tested with xdpyinfo and the X Test Suite passed and failed the
exact same tests before and after this extension was enabled.
XTEST, RECORD, DEC-XTRAP (supported) and XTestExtension1 (not
supported)
The XTEST and RECORD extension were developed by the X
Consortium for use in the X Test Suite and are supported as a
standard in the X11R6 tree. They are also supported in Xdmx.
When X Test Suite tests that make use of the XTEST extension
are run, Xdmx passes and fails exactly the same tests as does a
standard XFree86 X server. When the rcrdtest test (a part of
the X Test Suite that verifies the RECORD extension) is run,
Xdmx passes and fails exactly the same tests as does a standard
XFree86 X server.
There are two older XTEST-like extensions: DEC-XTRAP and
XTestExtension1. The XTestExtension1 extension was developed
for use by the X Testing Consortium for use with a test suite
that eventually became (part of?) the X Test Suite. Unlike
XTEST, which only allows events to be sent to the server, the
XTestExtension1 extension also allowed events to be recorded
(similar to the RECORD extension). The second is the DEC-XTRAP
extension that was developed by the Digital Equipment
Corporation.
The DEC-XTRAP extension is available from Xdmx and has been
tested with the xtrap* tools which are distributed as standard
X11R6 clients.
The XTestExtension1 is not supported because it does not appear
to be used by any modern X clients (the few that support it
also support XTEST) and because there are no good methods
available for testing that it functions correctly (unlike XTEST
and DEC-XTRAP, the code for XTestExtension1 is not part of the
standard X server source tree, so additional testing is
important).
Most of these extensions are documented in the X11R6 source
tree. Further, several original papers exist that this author
was unable to locate -- for completeness and historical
interest, citations are provide:
XRECORD
Martha Zimet. Extending X For Recording. 8th Annual X Technical
Conference Boston, MA January 24-26, 1994.
DEC-XTRAP
Dick Annicchiarico, Robert Chesler, Alan Jamison. XTrap
Architecture. Digital Equipment Corporation, July 1991.
XTestExtension1
Larry Woestman. X11 Input Synthesis Extension Proposal. Hewlett
Packard, November 1991.
MIT-MISC (not supported)
The MIT-MISC extension is used to control a bug-compatibility
flag that provides compatibility with xterm programs from X11R1
and X11R2. There does not appear to be a single client
available that makes use of this extension and there is not way
to verify that it works correctly. The Xdmx server does not
support MIT-MISC.
SCREENSAVER (not supported)
This extension provides special support for the X screen saver.
It was tested with beforelight, which appears to be the only
client that works with it. When Xinerama was not active,
beforelight behaved as expected. However, when Xinerama was
active, beforelight did not behave as expected. Further, when
this extension is not active, xscreensaver (a widely-used X
screen saver program) did not behave as expected. Since this
extension is not Xinerama-aware and is not commonly used with
expected results by clients, we have left this extension
disabled at this time.
GLX (supported)
The GLX extension provides OpenGL and GLX windowing support. In
Xdmx, the extension is called glxProxy, and it is Xinerama
aware. It works by either feeding requests forward through Xdmx
to each of the back-end servers or handling them locally. All
rendering requests are handled on the back-end X servers. This
code was donated to the DMX project by SGI. For the X Test
Suite results comparison, see below.
RENDER (supported)
The X Rendering Extension (RENDER) provides support for digital
image composition. Geometric and text rendering are supported.
RENDER is partially Xinerama-aware, with text and the most
basic compositing operator; however, its higher level
primitives (triangles, triangle strips, and triangle fans) are
not yet Xinerama-aware. The RENDER extension is still under
development, and is currently at version 0.8. Additional
support will be required in DMX as more primitives and/or
requests are added to the extension.
There is currently no test suite for the X Rendering Extension;
however, there has been discussion of developing a test suite
as the extension matures. When that test suite becomes
available, additional testing can be performed with Xdmx. The X
Test Suite passed and failed the exact same tests before and
after this extension was enabled.
Summary
To summarize, the following extensions are currently supported:
BIG-REQUESTS, DEC-XTRAP, DMX, DPMS,
Extended-Visual-Information, GLX, LBX, RECORD, RENDER,
SECURITY, SHAPE, SYNC, X-Resource, XC-APPGROUP, XC-MISC,
XFree86-Bigfont, XINERAMA, XInputExtension, XKEYBOARD, and
XTEST.
The following extensions are not supported at this time:
DOUBLE-BUFFER, FontCache, MIT-SCREEN-SAVER, MIT-SHM,
MIT-SUNDRY-NONSTANDARD, TOG-CUP, XFree86-DGA, XFree86-Misc,
XFree86-VidModeExtension, XTestExtensionExt1, and XVideo.
Additional Testing with the X Test Suite
XFree86 without XTEST
After the release of XFree86 4.3.0, we retested the XFree86 X
server with and without using the XTEST extension. When the
XTEST extension was not used for testing, the XFree86 4.3.0
server running on our usual test system with a Radeon VE card
reported unexpected failures in the following tests:
XListPixmapFormats: Test 1
XChangeKeyboardControl: Tests 9, 10
XGetDefault: Test 5
XRebindKeysym: Test 1
XFree86 with XTEST
When using the XTEST extension, the XFree86 4.3.0 server
reported the following errors:
XListPixmapFormats: Test 1
XChangeKeyboardControl: Tests 9, 10
XGetDefault: Test 5
XRebindKeysym: Test 1
XAllowEvents: Tests 20, 21, 24
XGrabButton: Tests 5, 9-12, 14, 16, 19, 21-25
XGrabKey: Test 8
XSetPointerMapping: Test 3
XUngrabButton: Test 4
While these errors may be important, they will probably be
fixed eventually in the XFree86 source tree. We are
particularly interested in demonstrating that the Xdmx server
does not introduce additional failures that are not known
Xinerama failures.
Xdmx with XTEST, without Xinerama, without GLX
Without Xinerama, but using the XTEST extension, the following
errors were reported from Xdmx (note that these are the same as
for the XFree86 4.3.0, except that XGetDefault no longer
fails):
XListPixmapFormats: Test 1
XChangeKeyboardControl: Tests 9, 10
XRebindKeysym: Test 1
XAllowEvents: Tests 20, 21, 24
XGrabButton: Tests 5, 9-12, 14, 16, 19, 21-25
XGrabKey: Test 8
XSetPointerMapping: Test 3
XUngrabButton: Test 4
Xdmx with XTEST, with Xinerama, without GLX
With Xinerama, using the XTEST extension, the following errors
were reported from Xdmx:
XListPixmapFormats: Test 1
XChangeKeyboardControl: Tests 9, 10
XRebindKeysym: Test 1
XAllowEvents: Tests 20, 21, 24
XGrabButton: Tests 5, 9-12, 14, 16, 19, 21-25
XGrabKey: Test 8
XSetPointerMapping: Test 3
XUngrabButton: Test 4
XCopyPlane: Tests 13, 22, 31 (well-known XTEST/Xinerama interac
tion issue)
XDrawLine: Test 67
XDrawLines: Test 91
XDrawSegments: Test 68
Note that the first two sets of errors are the same as for the
XFree86 4.3.0 server, and that the XCopyPlane error is a
well-known error resulting from an XTEST/Xinerama interaction
when the request crosses a screen boundary. The XDraw* errors
are resolved when the tests are run individually and they do
not cross a screen boundary. We will investigate these errors
further to determine their cause.
Xdmx with XTEST, with Xinerama, with GLX
With GLX enabled, using the XTEST extension, the following
errors were reported from Xdmx (these results are from early
during the Phase IV development, but were confirmed with a late
Phase IV snapshot):
XListPixmapFormats: Test 1
XChangeKeyboardControl: Tests 9, 10
XRebindKeysym: Test 1
XAllowEvents: Tests 20, 21, 24
XGrabButton: Tests 5, 9-12, 14, 16, 19, 21-25
XGrabKey: Test 8
XSetPointerMapping: Test 3
XUngrabButton: Test 4
XClearArea: Test 8
XCopyArea: Tests 4, 5, 11, 14, 17, 23, 25, 27, 30
XCopyPlane: Tests 6, 7, 10, 19, 22, 31
XDrawArcs: Tests 89, 100, 102
XDrawLine: Test 67
XDrawSegments: Test 68
Note that the first two sets of errors are the same as for the
XFree86 4.3.0 server, and that the third set has different
failures than when Xdmx does not include GLX support. Since the
GLX extension adds new visuals to support GLX's visual configs
and the X Test Suite runs tests over the entire set of visuals,
additional rendering tests were run and presumably more of them
crossed a screen boundary. This conclusion is supported by the
fact that nearly all of the rendering errors reported are
resolved when the tests are run individually and they do no
cross a screen boundary.
Further, when hardware rendering is disabled on the back-end
displays, many of the errors in the third set are eliminated,
leaving only:
XClearArea: Test 8
XCopyArea: Test 4, 5, 11, 14, 17, 23, 25, 27, 30
XCopyPlane: Test 6, 7, 10, 19, 22, 31
Conclusion
We conclude that all of the X Test Suite errors reported for
Xdmx are the result of errors in the back-end X server or the
Xinerama implementation. Further, all of these errors that can
be reasonably fixed at the Xdmx layer have been. (Where
appropriate, we have submitted patches to the XFree86 and
Xinerama upstream maintainers.)
Dynamic Reconfiguration
During this development phase, dynamic reconfiguration support
was added to DMX. This support allows an application to change
the position and offset of a back-end server's screen. For
example, if the application would like to shift a screen
slightly to the left, it could query Xdmx for the screen's
<x,y> position and then dynamically reconfigure that screen to
be at position <x+10,y>. When a screen is dynamically
reconfigured, input handling and a screen's root window
dimensions are adjusted as needed. These adjustments are
transparent to the user.
Dynamic reconfiguration extension
The application interface to DMX's dynamic reconfiguration is
through a function in the DMX extension library:
Bool DMXReconfigureScreen(Display *dpy, int screen, int x, int y)
where dpy is DMX server's display, screen is the number of the
screen to be reconfigured, and x and y are the new upper,
left-hand coordinates of the screen to be reconfigured.
The coordinates are not limited other than as required by the X
protocol, which limits all coordinates to a signed 16 bit
number. In addition, all coordinates within a screen must also
be legal values. Therefore, setting a screen's upper, left-hand
coordinates such that the right or bottom edges of the screen
is greater than 32,767 is illegal.
Bounding box
When the Xdmx server is started, a bounding box is calculated
from the screens' layout given either on the command line or in
the configuration file. This bounding box is currently fixed
for the lifetime of the Xdmx server.
While it is possible to move a screen outside of the bounding
box, it is currently not possible to change the dimensions of
the bounding box. For example, it is possible to specify
coordinates of <-100,-100> for the upper, left-hand corner of
the bounding box, which was previously at coordinates <0,0>. As
expected, the screen is moved down and to the right; however,
since the bounding box is fixed, the left side and upper
portions of the screen exposed by the reconfiguration are no
longer accessible on that screen. Those inaccessible regions
are filled with black.
This fixed bounding box limitation will be addressed in a
future development phase.
Sample applications
An example of where this extension is useful is in setting up a
video wall. It is not always possible to get everything
perfectly aligned, and sometimes the positions are changed
(e.g., someone might bump into a projector). Instead of
physically moving projectors or monitors, it is now possible to
adjust the positions of the back-end server's screens using the
dynamic reconfiguration support in DMX.
Other applications, such as automatic setup and calibration
tools, can make use of dynamic reconfiguration to correct for
projector alignment problems, as long as the projectors are
still arranged rectilinearly. Horizontal and vertical keystone
correction could be applied to projectors to correct for
non-rectilinear alignment problems; however, this must be done
external to Xdmx.
A sample test program is included in the DMX server's examples
directory to demonstrate the interface and how an application
might use dynamic reconfiguration. See dmxreconfig.c for
details.
Additional notes
In the original development plan, Phase IV was primarily
devoted to adding OpenGL support to DMX; however, SGI became
interested in the DMX project and developed code to support
OpenGL/GLX. This code was later donated to the DMX project and
integrated into the DMX code base, which freed the DMX
developers to concentrate on dynamic reconfiguration (as
described above).
Doxygen documentation
Doxygen is an open-source (GPL) documentation system for
generating browseable documentation from stylized comments in
the source code. We have placed all of the Xdmx server and DMX
protocol source code files under Doxygen so that comprehensive
documentation for the Xdmx source code is available in an
easily browseable format.
Valgrind
Valgrind, an open-source (GPL) memory debugger for Linux, was
used to search for memory management errors. Several memory
leaks were detected and repaired. The following errors were not
addressed:
1. When the X11 transport layer sends a reply to the client,
only those fields that are required by the protocol are
filled in -- unused fields are left as uninitialized memory
and are therefore noted by valgrind. These instances are
not errors and were not repaired.
2. At each server generation, glxInitVisuals allocates memory
that is never freed. The amount of memory lost each
generation approximately equal to 128 bytes for each
back-end visual. Because the code involved is automatically
generated, this bug has not been fixed and will be referred
to SGI.
3. At each server generation, dmxRealizeFont calls
XLoadQueryFont, which allocates a font structure that is
not freed. dmxUnrealizeFont can free the font structure for
the first screen, but cannot free it for the other screens
since they are already closed by the time dmxUnrealizeFont
could free them. The amount of memory lost each generation
is approximately equal to 80 bytes per font per back-end.
When this bug is fixed in the the X server's
device-independent (dix) code, DMX will be able to properly
free the memory allocated by XLoadQueryFont.
RATS
RATS (Rough Auditing Tool for Security) is an open-source (GPL)
security analysis tool that scans source code for common
security-related programming errors (e.g., buffer overflows and
TOCTOU races). RATS was used to audit all of the code in the
hw/dmx directory and all "High" notations were checked
manually. The code was either re-written to eliminate the
warning, or a comment containing "RATS" was inserted on the
line to indicate that a human had checked the code. Unrepaired
warnings are as follows:
1. Fixed-size buffers are used in many areas, but code has
been added to protect against buffer overflows (e.g.,
XmuSnprint). The only instances that have not yet been
fixed are in config/xdmxconfig.c (which is not part of the
Xdmx server) and input/usb-common.c.
2. vprintf and vfprintf are used in the logging routines. In
general, all uses of these functions (e.g., dmxLog) provide
a constant format string from a trusted source, so the use
is relatively benign.
3. glxProxy/glxscreens.c uses getenv and strcat. The use of
these functions is safe and will remain safe as long as
ExtensionsString is longer then GLXServerExtensions
(ensuring this may not be ovious to the casual programmer,
but this is in automatically generated code, so we hope
that the generator enforces this constraint).