Disable vertical sync for glxgears
Sometimes you need to check whether you Linux 3D acceleration is really working (besides the glxinfo output). This can be quickly done by the glxgears tool. However, the FPS are often limited to the displays vertical refresh rate (i.e. 60 fps). So the tool becomes more or less useless since even a software render can produce 60FPS glxgears easily on modern CPUs.
I found it rather hard to get a quick and easy solution for this, I answer my own question. Hopefully it saves your time.
Solution 1:
The vblank_mode environment variable does the trick. You should then get several hundreds FPS on modern hardware. And you are now able to compare the results with others.
$> vblank_mode=0 glxgears
Solution 2:
If you're using the NVIDIA closed-source drivers you can vary the vertical sync mode on the fly using the __GL_SYNC_TO_VBLANK environment variable:
~$ __GL_SYNC_TO_VBLANK=1 glxgears
Running synchronized to the vertical refresh. The framerate should be
approximately the same as the monitor refresh rate.
299 frames in 5.0 seconds = 59.631 FPS
~$ __GL_SYNC_TO_VBLANK=0 glxgears
123259 frames in 5.0 seconds = 24651.678 FPS
This works for me on Ubuntu 14.04 using the 346.46 NVIDIA drivers.
Solution 3:
For Intel graphics and AMD/ATI opensource graphics drivers
Find the "Device" section of /etc/X11/xorg.conf which contains one of the following directives:
Driver "intel"Driver "radeon"Driver "fglrx"
And add the following line to that section:
Option "SwapbuffersWait" "false"
And run your application with vblank_mode environment variable set to 0:
$ vblank_mode=0 glxgears
For Nvidia graphics with the proprietary Nvidia driver
$ echo "0/SyncToVBlank=0" >> ~/.nvidia-settings-rc
The same change can be made in the nvidia-settings GUI by unchecking the option at X Screen 0 / OpenGL Settings / Sync to VBlank. Or, if you'd like to just test the setting without modifying your ~/.nvidia-settings-rc file you can do something like:
$ nvidia-settings --load-config-only --assign="SyncToVBlank=0" # disable vertical sync
$ glxgears # test it out
$ nvidia-settings --load-config-only # restore your original vertical sync setting
Solution 4:
Putting the other answers all together, here's a command line that will work:
env vblank_mode=0 __GL_SYNC_TO_VBLANK=0 glxgears
This has the advantages of working for both Mesa and NVidia drivers, and not requiring any changes to configuration files.
Solution 5:
Disabling the Sync to VBlank checkbox in nvidia-settings (OpenGL Settings tab) does the trick for me.