[Mesa-stable] [PATCH 3/3] glx/dri3: Request non-vsynced Present for swapinterval zero.

[Keith Packard]

Mario Kleiner <mario.kleiner.de at gmail.com> writes:

> Hmm. For benchmarking i think i'd consider that a mild form of cheating. 
> You get higher fps because you skip processing like the whole gpu blit 
> overhead and host processing overhead for queuing / validating / 
> processing the copy command in the command stream, so the benchmark 
> numbers don't translate very well anymore in how the system would behave 
> in a non-benchmark situation?

It's still a very useful mode -- imagine wanting the lowest possible
latency between the user and the display; normally, you process input
and generate a frame just after vblank, then (if the rendering is really
quick), end up waiting most of the frame time not doing anything before
finally updating it at the next vblank.

With vblank_mode=0 and DRI3, you have the ability to try and generate
another frame before vblank comes; if you manage, then you get that data
on the screen, rather than the older version.

So, it offers latency closer to the tearing vblank_mode=0 but without
any tearing.

That's why I did it; the fact that it offers a small performance benefit
for benchmarks is an unintentional bonus feature.

-- 
keith.packard at intel.com
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