vblank_mode=0 glxgears
ATTENTION: default value of option vblank_mode overridden by environment.
ATTENTION: default value of option vblank_mode overridden by environment.
27529 frames in 5.0 seconds = 5505.764 FPS
XIO:  fatal IO error 11 (Resource temporarily unavailable) on X server ":0"
      after 94578 requests (94578 known processed) with 0 events remaining.
sp@ik:[~]: vblank_mode=0 optirun glxgears
ATTENTION: default value of option vblank_mode overridden by environment.
ATTENTION: default value of option vblank_mode overridden by environment.
ATTENTION: default value of option vblank_mode overridden by environment.
ATTENTION: default value of option vblank_mode overridden by environment.
ATTENTION: default value of option vblank_mode overridden by environment.
3927 frames in 5.0 seconds = 785.298 FPS
4202 frames in 5.0 seconds = 840.286 FPS
XIO:  fatal IO error 11 (Resource temporarily unavailable) on X server ":0"
      after 37 requests (37 known processed) with 0 events remaining.
X Error of failed request:  BadDrawable (invalid Pixmap or Window parameter)
  Major opcode of failed request:  154 (DRI2)
  Minor opcode of failed request:  8 (DRI2SwapBuffers           )
  Resource id in failed request:  0x4c00002
  Serial number of failed request:  23616
  Current serial number in output stream:  23617