Disable vertical sync for glxgears

Question

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.

Answer 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 

Answer 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.