I was trying to see how fast I could fill/swap on
/dev/fb0 with something to the effect of:
while :; do head -c $SIZE /dev/erg > /dev/fb0; head -c $SIZE /dev/zero > /dev/fb0; done
/dev/erg is a character device that provides a constant stream of "erg".)
It tore quite a bit--clearly, this doesn't actually respect vsync settings.
I'm aware this isn't the normal use case for
/dev/fb0 or the framebuffer devices in general (and also that they're really old and not favorable compared to drm, etc.), but what was more surprising is that I can't see any way of detecting/doing vsync with the framebuffer devices in general. Does one exist, and how might one use it?
For at least this case, the display driver is i915.