[Mesa-dev] [PATCH v3 5/7] radeonsi: Implement DCC fast clear.

Bas Nieuwenhuizen bas at basnieuwenhuizen.nl
Fri Oct 23 04:30:08 PDT 2015

On Fri, Oct 23, 2015 at 12:50 PM, Marek Olšák <maraeo at gmail.com> wrote:
> On Fri, Oct 23, 2015 at 12:17 PM, Bas Nieuwenhuizen
> <bas at basnieuwenhuizen.nl> wrote:
>> On Thu, Oct 22, 2015 at 12:12 PM, Marek Olšák <maraeo at gmail.com> wrote:
>>>> diff --git a/src/gallium/drivers/radeonsi/si_descriptors.c b/src/gallium/drivers/radeonsi/si_descriptors.c
>>>> index 5548cba3..a277fa5 100644
>>>> --- a/src/gallium/drivers/radeonsi/si_descriptors.c
>>>> +++ b/src/gallium/drivers/radeonsi/si_descriptors.c
>>>> @@ -234,7 +234,7 @@ static void si_set_sampler_views(struct pipe_context *ctx,
>>>>                         } else {
>>>>                                 samplers->depth_texture_mask &= ~(1 << slot);
>>>>                         }
>>>> -                       if (rtex->cmask.size || rtex->fmask.size) {
>>>> +                       if (rtex->cmask.size || rtex->fmask.size || rtex->surface.dcc_enabled) {
>>>>                                 samplers->compressed_colortex_mask |= 1 << slot;
>>> I'd like this flag to be set only when dirty_level_mask is non-zero.
>>> Setting this for all textures that have DCC is quite expensive in draw
>>> calls.
>> I think this code is incorrect even without considering DCC. If we do
>> a fast clear on a surface which allocates a cmask and then use that
>> surface as a texture without calling set_sampler_views in between
>> (because it was bound before) we get a stale compressed_colortex_mask.
>> Some testing shows that this can be triggered using OpenGL, although
>> the GL_ARB_texture_barrier extension may be needed to make the result
>> not undefined per the specification.
> In that case, we should decompress in texture_barrier and not in draw calls.
> Marek

texture_barrier does not need to be called though, the language
changes might be needed.

Basically the test is

fbo1, fbo2 framebuffers with 1 color buffer each:

bind fbo2 as texture
clear fbo1 using shader
bind fbo1 as texture
clear fbo2 using shader
clear fbo1 using clear (which results in cmask being allocated for fbo1)
bind fbo2 as texture
copy fbo2 to fbo1 using copy shader (which wrongly does not decompress fbo1)

If the clear shader has an unused sampler2D, then we bind fbo1 as a
texture before the clear and do not rebind it afterwards.

Note that the normal clear is the only one for which we have a
rendering feedback loop, and it should not fetch from any texture at
all. I don't think we need a texture barrier for that.

I would think this would be most easily fixed by recomputing
compressed_colortex_mask after a fast clear.

- Bas

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