Red Hat Bugzilla – Bug 36994
XShmGetImage() is very slow when acceleration is turned on
Last modified: 2007-04-18 12:32:46 EDT
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User-Agent: Mozilla/4.75 [en] (X11; U; Linux 2.2.16-22 i686)
Using shared memory for moving image data between the X server and the
graphical application is very slow when server acceleration is activated.
This was not the case in previous XFree86 versions.
On my PIII 933MHz/RIVA TNT2/i815, moving a 800x600 8-bit image with
XShmGetImage() takes around 72 milliseconds with accerelation turned on, as
is the default setup. When turning off acceleration with 'Option "NoAccel"
"1"' in /etc/X11/XF86Config-4, this drops to the more reasonable 3
Similar slowdowns are noticed with the same software on a Celeron
Steps to Reproduce:
1. Install Red Hat 7.1; X server acceleration is default set to active
2. Run an application which moves image data around with XShmGetImage()
3. Notice low framerate
4. Turn off acceleration with Option "NoAccel" "1" in XF86Config-4
5. Framerate increases dramatically
The tested application is our Olex seabed mapping and visualisation system,
previously installed on several hundred Red Hat 5.1 to 7.0 systems with
XFree86 3.3.x. A demonstration copy can be downloaded from www.olex.no.
Attach your config file and X server logs using the "Create a new attachment"
Please feel free to reopen this report after attaching the requested
information, if this is still a problem.