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loader/dri3: Overhaul dri3_update_num_back 

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@lists.freedesktop.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97260
Reviewed-by: Frank Binns <frank.binns@imgtec.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
This commit is contained in:
Michel Dänzer 2016-08-17 17:02:04 +09:00 committed by Michel Dänzer
parent 2301705dee
commit 1e3218bc5b
1 changed files with 6 additions and 9 deletions
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15
src/loader/loader_dri3_helper.c
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@ -68,15 +68,12 @@ dri3_fence_await(xcb_connection_t *c, struct loader_dri3_buffer *buffer)
static void
dri3_update_num_back(struct loader_dri3_drawable *draw)
{
draw->num_back = 1;
if (draw->flipping) {
if (!draw->is_pixmap &&
!(draw->present_capabilities & XCB_PRESENT_CAPABILITY_ASYNC))
draw->num_back++;
draw->num_back++;
}
if (draw->vtable->get_swap_interval(draw) == 0)
draw->num_back++;
if (draw->flipping)
draw->num_back = 3;
else if (draw->vtable->get_swap_interval(draw) != 0)
draw->num_back = 2;
else
draw->num_back = 1;
}
void