[Mesa-dev] [PATCH] i965/blit: Remove Yf/Ys tiled check under a FIXME at can_fast_copy_blit

[Anuj Phogat]

On Tue, Dec 6, 2016 at 10:58 AM, Alejandro Piñeiro <apinheiro at igalia.com> wrote:
> The FIXME suggest that the check should be removed.
>
Only if we see any performance or feature benefits in doing that.
Last I checked I didn't see any performance benefits on Skylake.
I also couldn't figure out the cause of random failure in a piglit test:
 ./bin/texelFetch fs sampler2DMSArray 4 98x1x9-98x129x9 -auto -fbo

I'm still seeing this failure when I tested your patch with Jenkins CI system.
Test passes when I run it locally on my system.

> This change helps the following test:
> GL45-CTS.texture_cube_map_array.color_depth_attachments
>
> to pass consistently on Skylake GT3e. Without this patch, on
> Skylake GT3e that test has a ~76% pass rate, with some random
> intel_do_flush_locked errors now and then.
>
By removing this check you're actually enabling fast copy blit on SKL+
for all the tiling formats. So, now the driver will use XY_FAST_COPY_BLT
in place of XY_SRC_COPY_BLT. If this change is fixing a test case for
you, that's not because this is the right fix, but that's because you're
avoiding to use XY_SRC_COPY_BLT.
XY_SRC_COPY_BLT might be causing intel_do_flush_locked errors
and the test failure. We need to dig in there to find the real cause.

> It works fine on Skylake GT2, though.
> ---
>
> I didn't analyze too much the code. It was more git history analysis.
>
> When I started to work to solve that test, I remembered that there was
> a time in the past that worked, so I just did a git bisect. The more
> recent bad commit I found was df210f. In any case, that one just fixed
> that check, as became broken with commit 0c02d7. The one that added
> the check (and the FIXME) was commit 412c8c.
>
> As the commit message says, that FIXME seems to suggest that is a
> provisional change. Although I recognize that the failure is really
> specific (for a Skylake model, not failing always), removing the check
> gets the test pass consistently, and as far as I see, it didn't
> introduce any regression.
>
>  src/mesa/drivers/dri/i965/intel_blit.c | 8 --------
>  1 file changed, 8 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/intel_blit.c b/src/mesa/drivers/dri/i965/intel_blit.c
> index 03a35ee..9f3b4d1 100644
> --- a/src/mesa/drivers/dri/i965/intel_blit.c
> +++ b/src/mesa/drivers/dri/i965/intel_blit.c
> @@ -487,14 +487,6 @@ can_fast_copy_blit(struct brw_context *brw,
>     if (brw->gen < 9)
>        return false;
>
> -   /* Enable fast copy blit only if the surfaces are Yf/Ys tiled.
> -    * FIXME: Based on performance data, remove this condition later to
> -    * enable for all types of surfaces.
> -    */
> -   if (src_tr_mode == INTEL_MIPTREE_TRMODE_NONE &&
> -       dst_tr_mode == INTEL_MIPTREE_TRMODE_NONE)
> -      return false;
> -
>     if (logic_op != GL_COPY)
>        return false;
>
> --
> 2.9.3
>