On 26/04/2019 10:08, Michel Dänzer wrote:
On 2019-04-26 4:06 a.m., Marek Olšák wrote:
From: Marek Olšák <marek.ol...@amd.com>
It's done by:
- decrease the number of frames in flight by 1
- flush before throttling in SwapBuffers
(instead of wait-then-flush, do flush-then-wait)
The improvement is apparent with Unigine Heaven.
Previously:
draw frame 2
wait frame 0
flush frame 2
present frame 2
The input lag is 2 frames.
Now:
draw frame 2
flush frame 2
wait frame 1
present frame 2
The input lag is 1 frame. Flushing is done before waiting, because
otherwise the device would be idle after waiting.
Nice idea. Not sure offhand about all ramifications, but certainly worth
a go.
Nine is affected because it also uses the pipe cap.
---
src/gallium/auxiliary/util/u_screen.c | 2 +-
src/gallium/state_trackers/dri/dri_drawable.c | 20 +++++++++----------
2 files changed, 11 insertions(+), 11 deletions(-)
diff --git a/src/gallium/auxiliary/util/u_screen.c
b/src/gallium/auxiliary/util/u_screen.c
index 27f51e0898e..410f17421e6 100644
--- a/src/gallium/auxiliary/util/u_screen.c
+++ b/src/gallium/auxiliary/util/u_screen.c
@@ -349,21 +349,21 @@ u_pipe_screen_get_param_defaults(struct pipe_screen
*pscreen,
case PIPE_CAP_MAX_VARYINGS:
return 8;
case PIPE_CAP_COMPUTE_GRID_INFO_LAST_BLOCK:
return 0;
case PIPE_CAP_COMPUTE_SHADER_DERIVATIVES:
return 0;
case PIPE_CAP_MAX_FRAMES_IN_FLIGHT:
- return 2;
+ return 1;
This might be slightly misleading, as there can still be two frames in
flight (on the GPU) at the same time. Might be better to leave this at 2
(so Nine isn't affected) and adjust its treatment in
src/gallium/state_trackers/dri/dri_drawable.c .
Checking what gallium nine does currently, it seems we already do flush
then wait,
however we call swap_fences_pop_front and swap_fences_push_back in the
reverse order compared to your patch.
We compensate by taking PIPE_CAP_MAX_FRAMES_IN_FLIGHT + 1
In conclusion, with the proposed patch, gl and nine should have the same
behaviour (and thus if gl benefits from a value of 1, nine should as well).
I haven't have noticed input lag, I guess I have to test on heaven if
you see a difference.
How can I slow down my gpu to test that ? I use to use the
/sys/kernel/debug/dri/0/ vars to force low dpm, but it doesn't seem to
be possible anymore as the related files are gone (rx480) ?
Axel
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