First of all, sudo aptitude install mesa-utils. Then run in a Terminal/Konsole glxgears, and wait for ~15 seconds; if your FPS is ~400 or less, then you do have sluggish video performance (usually manifesting itself as slow scrolling in Firefox/Iceweasel, slow window switching/minimziing/maximizing etc).

After reading through several forums and bug reports and blog posts, I’ve ended with the following modifications to my /etc/X11/xorg.conf:

1. backup your current xorg.conf: sudo cp /etc/X11/xorg.conf /etc/X11/xorg.conf.before-exa
2. open your /etc/X11/xorg.conf with a favourite editor; I’ve added these lines to section “module”:
   

   Load “dbe”
   Load “xtrap”
   Load “record”
   Load “GLcore”

   These are not really performance-related and could be skipped; I’m giving them here, because they were suggested as default entries by dexconf or some other xorg.conf-generator utility. Again – they are not supposed to improve performance, so you can skip these.

3. my “Device” section is now:
   

   Section “Device”
   Identifier “Intel Corporation 82915G/GV/910GL Integrated Graphics Controller”
   BoardName “82915G/GV/910GL Integrated Graphics Controller”
   Vendorname “Intel Corporation”
   #Driver “i810″
   Driver “intel”
   BusID “PCI:0:2:0″
   Option “DRI” “true”
   Option “AccelMethod” “exa”
   Option “MigrationHeuristic” “greedy”
   Option “ExaNoComposite” “false”
   EndSection

   Driver i810 (xserver-xorg-video-i810 package) was about 10-20 FPS slower than Driver intel (xserver-xorg-video-intel package) for me. The most important lines here are Option AccelMethod exa (which enables EXA acceleration instead of the older XAA; if you run 2.6.28 or later kernel, you can try UXA instead of EXA) and Option MigrationHeuristic greedy. Option ExaNoComposite false doesn’t make a difference for me, and Option DRI true might be redundant (didn’t bother trying to remove it).

4. at the end of xorg.conf I have two more sections:
   

   Section “DRI”
   Mode 0666
   EndSection

   Section “Extensions”
   Option “Composite” “enable”
   Option “MIT-SHM” “Yes”
   EndSection

5. sudo nano /etc/environment, and add one line: INTEL_BATCH=1 (if you have graphics stability issues or screen corruption – try removing this change first)
6. you can test if your xorg.conf is syntactically correct by running X -config /etc/X11/xorg.conf (provided that you edited this exact file)

This is it. Before these modifications, my FPS in glxgears was around 430; after these modifications it is ~915.

As time permits, I might try the XAA configuration, suggested at foolcontrol.

Update: with compiz enabled, XAA configuration recommended at foolcontrol is definitely faster in 2D.

Improvements, suggestions, corrections are welcome.

For the case of ATI (and ATI Mobility) Radeon series, the easiest procedure would be (doing all as root, or prepending sudo to all commands):

1. aptitude update, to ensure you’ve got the list of latest packages
2. aptitude install fglrx-driver fglrx-control fglrx-kernel-src, for the actual driver; I also installed fglrx-atieventsd and fglrx-glx (these are driver-recommended packages)
3. aptitude install module-assistant, required for building the kernel module
4. module-assistant prepare, to verify that you have everything needed for the module build procedure
5. module-assistant update
6. module-assistant auto-install fglrx, to build and install the fglrx kernel module
7. depmod -a
8. modprobe fglrx, to load the fglrx kernel module
9. aticonfig ––initial, to configure ATI’s device section in /etc/X11/xorg.conf (for more options, see aticonfig ––help)
10. reboot

That should make your ATI hardware work as expected, and make fgl_glxgears show gears again.

If everything went fine, then your movies will play smoother ;), and the output of fglrxinfo will look similar to

display: :0.0 screen: 0
OpenGL vendor string: ATI Technologies Inc.
OpenGL renderer string: ATI MOBILITY RADEON X600
OpenGL version string: 2.1.7769 Release

This procedure should be also possible for the latest ATI-provided installer-generated Debian packages (as described elsewhere), but I decided to stick to the repository version – this requires no extra tweaking.

For much more information, see the ATI Debian Installation Guide.

This post is based on the iwanabeguru’s response at Linux Forums.

There’s also another one, but provides read-only support.