[Mesa-dev] [PATCH 18/20] mesa: Rewrite the way uniforms are tracked and handled

[Marek Olšák]

On Thu, Jan 5, 2012 at 12:45 AM, Eric Anholt <eric at anholt.net> wrote:
> On Wed, 04 Jan 2012 03:28:12 -0800, Kenneth Graunke <kenneth at whitecape.org> wrote:
>> On 01/03/2012 09:43 PM, Marek Olšák wrote:
>> > This ProgramStringNotify call causes excessive shader recompilations
>> > in the game Cogs (from some Humble Bundle). Approximately 25% of
>> > in-game CPU time is spent on translating shaders and register
>> > allocation. If the shaders were larger, it would be much worse.
>> > Moreover, I have realized calling ProgramStringNotify is not needed
>> > for st/mesa in this case at all (I just comment it out if I want
>> > higher frame rates), because it doesn't use the prog->SamplerUnits
>> > array when translating shaders. The array is only used when we set
>> > samplers, so setting _NEW_TEXTURE is sufficient. It seems that i965
>> > could do the same thing. Another option would be to cache precompiled
>> > shaders, but that seems more complicated than doing what st/mesa does.
>> >
>> > Marek
>>
>> Yeah, I noticed that a while back too, but we never arrived at a
>> solution and it slipped off my radar.  I agree completely,
>> ProgramStringNotify is completely overkill and bogus.
>>
>> We actually already rely on _NEW_TEXTURE for all shader programs.  Since
>> the uniform code already flags _NEW_TEXTURE, we should be able to just
>> add the SamplerUnits array to the program key (specifically,
>> brw_sampler_prog_key_data), and that should take care of any state
>> dependent recompiles.  Then we wouldn't need ProgramStringNotify at all.
>>
>> Right?
>
> Well, since the data stored is part of the program, and when just
> changing programs _NEW_TEXTURE wouldn't get set, I think _NEW_PROGRAM is
> the flag you mean.  That would make a ton of sense to me -- if you
> depend on SamplerUnits for your program handling, go look at it when
> _NEW_PROGRAM is flagged.

I don't think this is about what makes sense in theory, but how each
driver handles SamplerUnits. st/mesa just rebinds textures, so it
expects _NEW_TEXTURE. i965 recompiles the fragment program, so it
expects _NEW_PROGRAM. The worst option would be to set both, but at
the same time it's the only option which would work for everybody now.

Marek