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Symptoms:

• With compiz enabled, some animations such as desktop switching or compiz cube view are not smooth and take longer to complete than previously.
• Scrolling in firefox is laggy
• Switching to 2D makes performance issues go away
• Switching compiz off makes performance significantly better
• 3D video game FPS measures are significantly lower than previously

Non-Symptoms:

• glxgears FPS drops. glxgears is not a benchmark, don't use it!

• CPU usage is high. Rather, see X/Troubleshooting/HighCPU instead.

• Memory usage is high. See X/Troubleshooting/HighMemory instead.

How It Works

tbd

Problem: /dev/dri/card0 is missing

The /dev/dri/card0 device file is provided by the Linux kernel. If the file is missing, it prevents hardware acceleration from working. See if reloading the kernel module makes it work:

 # Save your work first!
 $ sudo rmmod i915
 $ sudo modprobe i915
 $ lsmod | grep i915
 i915 65412 1
 drm 96424 2 i915
 $ sudo pkill X

Problem: Falling back to OpenGL software rendering

Check if you're using software or hardware 3D rendering via glxinfo|grep render.

1. Is properly using hardware rendering:

 bryce$ glxinfo | grep render
 direct rendering: Yes
 OpenGL renderer string: Mesa DRI Intel(R) 965GM GEM 20090114 x86/MMX/SSE2

2. Is falling back to software rendering:

 bryce$ glxinfo | grep render
 direct rendering: Yes
 OpenGL renderer string: Software Rendering

Having DRI disabled can lead to this. Check if it has been loaded; your Xorg.0.log should show something like this:

 bryce$ egrep "(GLX|DRI)" /var/log/Xorg.0.log
 (==) AIGLX enabled
 (II) Loading extension GLX
 (II) Loading extension XFree86-DRI
 (II) Loading extension DRI2
 (WW) intel(0): DRI2 requires UXA
 (II) intel(0): [DRI] installation complete
 (II) intel(0): 0x0077f000-0x0cd3ffff: DRI memory manager (202500 kB)
 (II) intel(0): direct rendering: XF86DRI Enabled
 (II) AIGLX: Screen 0 is not DRI2 capable
 (II) AIGLX: enabled GLX_SGI_make_current_read
 (II) AIGLX: enabled GLX_MESA_copy_sub_buffer
 (II) AIGLX: enabled GLX_SGI_swap_control and GLX_MESA_swap_control
 (II) AIGLX: enabled GLX_texture_from_pixmap with driver support
 (II) AIGLX: Loaded and initialized /usr/lib/dri/i965_dri.so
 (II) GLX: Initialized DRI GL provider for screen 0

3. Has no direct 3D rendering:

 bryce$ glxinfo | grep render
 direct rendering: No (If you want to find out why, try setting LIBGL_DEBUG=verbose)
 OpenGL renderer string: Mesa GLX Indirect

Problem: glxgears has low FPS

It is important to note and remember that glxgears is *not* a benchmark tool. It simply measures how fast the driver writes images to the screen, whereas most 3D applications are limited by render speed, not merely blit speed. Instead use a 3D game (flightgear, tremulous, etc.) that has a real rendering workload to make comparisons.

Too often when glxgears is quoted in a bug report, the reporter is simply misunderstanding the tool's output. For this reason mention of glxgears in a bug report is a quick way to get the report closed as invalid! Use other tools instead.

But for your own edification, here's some insights into what the glxgear number changes imply:

1. glxgears drops from XXXX to YYY

This is generally nothing to worry about. High glxgears numbers generally indicate excessively high screen repainting, so if this drops from say 1500 fps to 500 fps, it should not produce any noticeable performance impact.

2. glxgears drops from XXX to YYY

As in #1, these drops are *usually* nothing to worry about, especially if you haven't noticed any change in performance. In *some* cases if you notice a performance drop, glxgears numbers may drop as well, and there may indeed be a correlation. However, glxgears isn't a benchmark, so it does little good to post the numbers (indeed, if anything it flags your post as ill-informed on the subject!)

Instead, get before and after FPS measurements using a 3D game, such as sauerbraten, tuxracer, tremulous, or the like.

3. glxgears drops from XXX to YY (e.g. usually around ~50-60fps)

This may indicate that you have vblank syncing turned on. Is the glxgears fps roughly equal to the refresh rate of your monitor? (LCDs tend to operate at 60Hz, so 50-60fps is common in these cases)

If so, see the previous section for a discussion of vblank settings. Normally vblank is a GOOD thing, but it can cause side-effects. If you are experiencing performance impacts, try disabling vblank.

4. glxgears drops to 30fps or below

Any time glxgears returns fps less than your monitor's refresh rate, it definitely indicates a performance problem.

If the fps seems to hit at about half your monitor refresh rate, it indicates the graphics card is not synchronizing properly, and is missing every other frame request by the monitor.