[Mesa-dev] [PATCH 2/3] i965: Keep track of the per-thread scratch allocation in brw_stage_state.

[Kenneth Graunke]

On Saturday, June 11, 2016 2:50:27 PM PDT Francisco Jerez wrote:
> diff --git a/src/mesa/drivers/dri/i965/brw_program.c b/src/mesa/drivers/dri/i965/brw_program.c
> index 792f81b..9f822d2 100644
> --- a/src/mesa/drivers/dri/i965/brw_program.c
> +++ b/src/mesa/drivers/dri/i965/brw_program.c
> @@ -345,6 +345,23 @@ brw_get_scratch_bo(struct brw_context *brw,
>     }
>  }
>  
> +/**
> + * Reserve enough scratch space for the given stage to hold \p per_thread_size
> + * bytes times the given \p thread_count.
> + */
> +void
> +brw_alloc_stage_scratch(struct brw_context *brw,
> +                        struct brw_stage_state *stage_state,
> +                        unsigned per_thread_size,
> +                        unsigned thread_count)
> +{
> +   if (stage_state->per_thread_scratch < per_thread_size) {
> +      stage_state->per_thread_scratch = per_thread_size;
> +      brw_get_scratch_bo(brw, &stage_state->scratch_bo,
> +                         per_thread_size * thread_count);
> +   }
> +}
> +
>  void brwInitFragProgFuncs( struct dd_function_table *functions )
>  {
>     assert(functions->ProgramStringNotify == _tnl_program_string);

There may still be an obscure bug here: brw_get_scratch_bo() skips
allocating a new BO if old_bo->size >= size.  If old_bo->size were
actually the size we requested, then that would be fine, as we only
request a new BO when the size actually increases.

I'm concerned that libdrm's buffer cache may round up bo->size to
the next bucket size, or a page or something.  I don't remember the
details...it might be fine.

Still, I don't think the redundant check buys us anything.  How about
deleting brw_get_scratch_bo() and calling unreference/bo_alloc directly
from brw_alloc_stage_scratch()?  Seems simpler if nothing else.

With that changed, the series is:
Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>

Thanks so much for tracking this down!
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