[Mesa-dev] [PATCH 2/2] radeonsi: drop few partial flushes when uploading bindless descriptors

[Nicolai Hähnle]

On 29.06.2017 21:59, Samuel Pitoiset wrote:
> Only emit partial flushes when the underlying shader stages
> are using bindless samplers or images.
> 
> This gets rid of 4% of partial flushes in the DOW3 benchmark.

Do those flushes still trigger during play?

I'd think it should be possible to eliminate these partial flushes 
entirely. The logic is that you only ever need the wait in the first 
place when you're overriding a previously used descriptor.

So what you could do is add a counter (per context, I think?) which is 
incremented whenever a flush happens, and then release descriptors 
lazily based on that.

Alternatively (maybe easier, not sure): all shaders are guaranteed to 
have finished when the fence of a submit fires, so use that as the guard 
for lazily releasing descriptors.

Anyway, this patch is a nice first step.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle at amd.com>


> Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
> ---
>   src/gallium/drivers/radeonsi/si_descriptors.c | 18 ++++++++++++++++--
>   1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/src/gallium/drivers/radeonsi/si_descriptors.c b/src/gallium/drivers/radeonsi/si_descriptors.c
> index 88f7dcee959..7d8b3670887 100644
> --- a/src/gallium/drivers/radeonsi/si_descriptors.c
> +++ b/src/gallium/drivers/radeonsi/si_descriptors.c
> @@ -1934,14 +1934,28 @@ static void si_upload_bindless_descriptor(struct si_context *sctx,
>   
>   static void si_upload_bindless_descriptors(struct si_context *sctx)
>   {
> +	unsigned shader_uses_bindless_mask;
> +
>   	if (!sctx->bindless_descriptors_dirty)
>   		return;
>   
>   	/* Wait for graphics/compute to be idle before updating the resident
>   	 * descriptors directly in memory, in case the GPU is using them.
>   	 */
> -	sctx->b.flags |= SI_CONTEXT_PS_PARTIAL_FLUSH |
> -			 SI_CONTEXT_CS_PARTIAL_FLUSH;
> +	sctx->b.flags |= SI_CONTEXT_CS_PARTIAL_FLUSH;
> +
> +	/* To avoid unnecessary partial flushes, check which shader stages are
> +	 * using bindless samplers or images.
> +	 */
> +	shader_uses_bindless_mask = sctx->shader_uses_bindless_samplers_mask |
> +				    sctx->shader_uses_bindless_images_mask;
> +
> +	if (shader_uses_bindless_mask & (1 << PIPE_SHADER_FRAGMENT)) {
> +		sctx->b.flags |= SI_CONTEXT_PS_PARTIAL_FLUSH;
> +	} else if (shader_uses_bindless_mask) {
> +		sctx->b.flags |= SI_CONTEXT_VS_PARTIAL_FLUSH;
> +	}
> +
>   	si_emit_cache_flush(sctx);
>   
>   	util_dynarray_foreach(&sctx->resident_tex_handles,
> 


-- 
Lerne, wie die Welt wirklich ist,
Aber vergiss niemals, wie sie sein sollte.