You need to disable vsync like this when running glxgears:
vblank_mode=0 glxgears
Notice the higher than 59-60 fps results with vblank_mode=0:
ATTENTION: default value of option vblank_mode overridden by environment.
7919 frames in 5.0 seconds = 1583.704 FPS
8187 frames in 5.0 seconds = 1637.266 FPS
7441 frames in 5.0 seconds = 1488.072 FPS
7436 frames in 5.0 seconds = 1487.076 FPS
XIO: fatal IO error 11 (Resource temporarily unavailable) on X server ":0"
after 70679 requests (70679 known processed) with 0 events remaining.
Just running normal glxgears will only get you the screen vertical refresh which is a very silly default:
~ $ glxgearsRunning synchronized to the vertical refresh. The framerate should be
approximately the same as the monitor refresh rate.
296 frames in 5.0 seconds = 59.025 FPS
XIO: fatal IO error 11 (Resource temporarily unavailable) on X server ":0"
after 1205 requests (1205 known processed) with 0 events remaining.
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