[Mesa-dev] [PATCH] i965: Prefer Meta over the BLT for BlitFramebuffer.

[Ben Widawsky]

On Thu, Jan 15, 2015 at 01:41:14AM -0800, Kenneth Graunke wrote:
> There's some debate about whether we should use Meta or BLORP,
> but either should run circles around the BLT engine.
> 
> Improves performance in "copypixrate -blit -back" (from Mesa demos)
> by 232.037% +/- 3.15795% (n=10) on Broadwell GT3e.
> 
> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> ---
>  src/mesa/drivers/dri/i965/intel_fbo.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> Ben: this might be a good candidate for your braswell branch.
> 

I'll give it a run through the benchmarks assuming I can get a working machine.
I am always concerned about this kind of switch because it seems very benchmark
dependent to me. If we happen to have benchmarks which are extremely GPU/RCS
limited, I could only imagine this would hurt, for example.

Anyway, I'll let the data speak for itself when I have it. Thanks for giving me
new things to try.

> Jason: I bet this will affect your PBO upload path.  I suspect it may
> make it a lot faster on Gen8+, as you might've been getting the BLT
> engine when trying to use BlitFramebuffer.  I haven't tested.
> 
> diff --git a/src/mesa/drivers/dri/i965/intel_fbo.c b/src/mesa/drivers/dri/i965/intel_fbo.c
> index 37ac613f..b54c11d 100644
> --- a/src/mesa/drivers/dri/i965/intel_fbo.c
> +++ b/src/mesa/drivers/dri/i965/intel_fbo.c
> @@ -882,6 +882,13 @@ intel_blit_framebuffer(struct gl_context *ctx,
>     if (mask == 0x0)
>        return;
>  
> +   mask = _mesa_meta_BlitFramebuffer(ctx,
> +                                     srcX0, srcY0, srcX1, srcY1,
> +                                     dstX0, dstY0, dstX1, dstY1,
> +                                     mask, filter);
> +   if (mask == 0x0)
> +      return;
> +
>     if (brw->gen >= 8 && (mask & GL_STENCIL_BUFFER_BIT)) {
>        brw_meta_fbo_stencil_blit(brw_context(ctx),
>                                  srcX0, srcY0, srcX1, srcY1,
> @@ -899,13 +906,6 @@ intel_blit_framebuffer(struct gl_context *ctx,
>     if (mask == 0x0)
>        return;
>  
> -   mask = _mesa_meta_BlitFramebuffer(ctx,
> -                                     srcX0, srcY0, srcX1, srcY1,
> -                                     dstX0, dstY0, dstX1, dstY1,
> -                                     mask, filter);
> -   if (mask == 0x0)
> -      return;
> -
>     _swrast_BlitFramebuffer(ctx,
>                             srcX0, srcY0, srcX1, srcY1,
>                             dstX0, dstY0, dstX1, dstY1,
> -- 
> 2.2.1
>