[Mesa-dev] [PATCH] i965: disable blorp's linear filtering on SNB

[Ian Romanick]

On 03/28/2014 01:04 PM, Anuj Phogat wrote:
> On Thu, Mar 27, 2014 at 1:29 AM, Samuel Iglesias Gonsalvez
> <siglesias at igalia.com> wrote:
>> Commit 079bdba05f870807d3ed77fa3093cdb7727aa2fd enabled the use of BLORP
>> engine for single sample scaled blit with bilinear filter.
>>
>> However piglit fails when running fbo-blit-stretch test on SandyBridge.
>> This patch makes the code to fallback to other blit paths for SandyBridge.
> My thoughts:
> 
> - Yes, fbo-blit-stretch test passes on SNB with fallback blit paths. But similar
>    piglit tests fbo-blit-scaled-linear and fbo-attachments-blit-scaled-linear
>    continues to fail with small color differences with meta fallback. So, the
>    fallback helped one out of three linear scaled blit tests.
>    Note: Use git-89ccd11 to run other two tests. A later patch causes the tests
>    to assert fail on SNB.

Other work is progressing towards removing blorp completely.  If there
are cases that fail with the meta paths, those should get fixed.  I
think I'd want the meta paths fixed first, then disable the blorp path.

> - The meta fallback will possibly have some performance penalty and It will just
>    hide the linear filtering bug in blorp engine.

Theoretically, I think that's true.  I don't know how true it is in
practice.  I think there are a couple cases in Synmark that test this,
and Kerbal Space Program also uses a lot of scaled blits.  We should
check before and after performance of those.

> - Current output from blorp on SNB is little off from expected but still looks
>    visually correct. I would prefer a patch which fixes the issue in blorp.
> 
> Let's wait for more opinions on this.
>>
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=68365
>>
>> Signed-off-by: Samuel Iglesias Gonsalvez <siglesias at igalia.com>
>> ---
>>  src/mesa/drivers/dri/i965/brw_blorp_blit.cpp | 9 +++++++++
>>  1 file changed, 9 insertions(+)
>>
>> diff --git a/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp b/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
>> index 9e80935..a0a9a7b 100644
>> --- a/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
>> +++ b/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
>> @@ -251,6 +251,15 @@ try_blorp_blit(struct brw_context *brw,
>>     fixup_mirroring(mirror_y, srcY0, srcY1);
>>     fixup_mirroring(mirror_y, dstY0, dstY1);
>>
>> +   /* Linear filtering using blorp engine is failing on Sandybridge. So, fallback
>> +    * to other blit paths.
>> +    * See https://bugs.freedesktop.org/show_bug.cgi?id=68365
>> +    */
>> +   if ((brw->gen == 6) && (srcX1 - srcX0 != dstX1 - dstX0 ||
>> +                           srcY1 - srcY0 != dstY1 - dstY0) &&
>> +       filter == GL_LINEAR)
>> +          return false;
>> +
>>     /* If the destination rectangle needs to be clipped or scissored, do so.
>>      */
>>     if (!(clip_or_scissor(mirror_x, srcX0, srcX1, dstX0, dstX1,
>> --
>> 1.9.0
>>
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