Why is primusrun slower than optirun?
From Primus FAQ:
Q: Performance does not exceed 60 fps, I was getting more with optirun/VirtualGL.
A: This is the effect of vblank synchronisation. For benchmarking, you can use
vblank_mode=0 primusrun ..., but in practice this will probably only
waste power, as your LCD panel does not display more than 60 frames
per second anyway.