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

(Where /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.

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