[Mesa-dev] [PATCH] i965: Advertise 65536 for GL_MAX_UNIFORM_BLOCK_SIZE.

[Kenneth Graunke]

On Tuesday, September 08, 2015 08:50:41 PM Ian Romanick wrote:
> On 09/08/2015 06:04 PM, Kenneth Graunke wrote:
> > Our old value of 16384 is the minimum value.  DirectX apparently
> > requires 65536 at a minimum; that's also what nVidia and the Intel
> > Windows driver advertise.  AMD advertises MAX_INT.
> > 
> > Ilia Mirkin noticed that "Shadow Warrior" uses UBOs larger than 16k
> > on Nouveau, which advertises 65536 bytes for this limit.  Traces
> > captured on Nouveau don't work on i965 because our lower limit causes
> > the GLSL linker to reject the captured shaders.  While this isn't
> > important in and of itself, it does suggest that raising the limit
> > would be beneficial.
> > 
> > We can read linear buffers up to 2^27 bytes in size, so raising this
> > should be safe; we could probably even go larger.  For now, matching
> > nVidia and Intel/Windows seems like a good plan.
> > 
> > We have to reinitialize MaxCombinedUniformComponents as core Mesa will
> > have set it based on a stale value for MaxUniformBlockSize.
> > 
> > Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> > ---
> >  src/mesa/drivers/dri/i965/brw_context.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/src/mesa/drivers/dri/i965/brw_context.c b/src/mesa/drivers/dri/i965/brw_context.c
> > index 907b2a0..7c1c133 100644
> > --- a/src/mesa/drivers/dri/i965/brw_context.c
> > +++ b/src/mesa/drivers/dri/i965/brw_context.c
> > @@ -323,6 +323,15 @@ brw_initialize_context_constants(struct brw_context *brw)
> >  
> >     ctx->Const.StripTextureBorder = true;
> >  
> > +   ctx->Const.MaxUniformBlockSize = 65536;
> > +   for (int i = 0; i < MESA_SHADER_STAGES; i++) {
> > +      struct gl_program_constants *prog = &ctx->Const.Program[i];
> > +      prog->MaxUniformBlocks = 12;
> 
> Is this actually necessary?  It looks like this is that value already
> set in init_program_limits.  Either way, this patch is
> 
> Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>

You're right, setting prog->MaxUniformBlocks = 12 is unnecessary.

We do need to reset prog->MaxCombinedUniformComponents since
init_program_limits computed a value using a stale MaxUniformBlockSize.

I figured since the three values are related, we may as well just
explicitly initialize them all.  But if you'd prefer I take it out,
I'm fine with that too.  What do you prefer?

Thanks for the quick review!

--Ken

> > +      prog->MaxCombinedUniformComponents =
> > +         prog->MaxUniformComponents +
> > +         ctx->Const.MaxUniformBlockSize / 4 * prog->MaxUniformBlocks;
> > +   }
> > +
> >     ctx->Const.MaxDualSourceDrawBuffers = 1;
> >     ctx->Const.MaxDrawBuffers = BRW_MAX_DRAW_BUFFERS;
> >     ctx->Const.Program[MESA_SHADER_FRAGMENT].MaxTextureImageUnits = max_samplers;
> > 
> 
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