[Mesa-dev] [PATCH 6/7] intel: Drop gratuitous flush in PBO blit upload.

[Kenneth Graunke]

On 09/21/2011 10:15 AM, Eric Anholt wrote:
> Since the blit gets sequenced after other batchbuffer rendering like
> normal, there's no need to push things out early.
> ---
>  src/mesa/drivers/dri/intel/intel_tex_image.c |    3 ---
>  1 files changed, 0 insertions(+), 3 deletions(-)
> 
> diff --git a/src/mesa/drivers/dri/intel/intel_tex_image.c b/src/mesa/drivers/dri/intel/intel_tex_image.c
> index 9ae0aee..ac3489b 100644
> --- a/src/mesa/drivers/dri/intel/intel_tex_image.c
> +++ b/src/mesa/drivers/dri/intel/intel_tex_image.c
> @@ -196,9 +196,6 @@ try_pbo_upload(struct intel_context *intel,
>  
>     dst_stride = intelImage->mt->region->pitch;
>  
> -   if (drm_intel_bo_references(intel->batch.bo, dst_buffer))
> -      intel_flush(&intel->ctx);
> -
>     {
>        GLuint offset;
>        drm_intel_bo *src_buffer =

I'm a bit uncertain about this patch.  Is it possible to:
1. Render some stuff
2. TexImage to upload a PBO
3. Do more rendering, reading or writing the PBO
...all within the same batchbuffer?

The point of these flushes is to make sure the blit happens before any
further uses of the buffer.  If the current render batch can read from
the PBO, it'll get garbage; any writes it does would be clobbered by the
blit.

It's not obvious to me why this is unnecessary.