[Mesa-dev] [PATCH] loader/dri3: Overhaul dri3_update_num_back

[Eric Anholt]

Michel Dänzer <michel at daenzer.net> writes:

> From: Michel Dänzer <michel.daenzer at amd.com>
>
> Always use 3 buffers when flipping. With only 2 buffers, we have to wait
> for a flip to complete (which takes non-0 time even with asynchronous
> flips) before we can start working on the next frame. We were previously
> only using 2 buffers for flipping if the X server supports asynchronous
> flips, even when we're not using asynchronous flips. This could result
> in bad performance (the referenced bug report is an extreme case, where
> the inter-frame stalls were preventing the GPU from reaching its maximum
> clocks).
>
> I couldn't measure any performance boost using 4 buffers with flipping.
> Performance actually seemed to go down slightly, but that might have
> been just noise.
>
> Without flipping, a single back buffer is enough for swap interval 0,
> but we need to use 2 back buffers when the swap interval is non-0,
> otherwise we have to wait for the swap interval to pass before we can
> start working on the next frame. This condition was previously reversed.
>
> Cc: "12.0 11.2" <mesa-stable at lists.freedesktop.org>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97260
> Signed-off-by: Michel Dänzer <michel.daenzer at amd.com>

Reviewed-by: Eric Anholt <eric at anholt.net>
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