[Mesa-dev] r600: performance reading from staging texture

[Marek Olšák]

Hi,

The change looks good. I have commited it to Mesa.

Marek

On Fri, Aug 31, 2012 at 6:57 PM, Vic Lee <llyzs.vic at gmail.com> wrote:
> Hi,
>
> In my application, I need to read pixels back to system memory for every
> rendered frame. My approach is to create a chain of textures with
> PIPE_USAGE_STAGING flag, and copy the render target to the staging textures
> before reading them to avoid pipeline stall.
>
> Now I found out as in the patch below, there's a line of code checking
> whether the texture volume has more than 1024 pixels and will use a staging
> texture if so. However the texture I am mapping is already staging and can
> be surely mapped directly regardless of its volume. This checking does not
> make any sense for me and is causing significant performance penalty. I have
> tried removing it and nothing is broken, performance can go up 10-20% in my
> case.
>
> Please point it out if I missed anything here, otherwise I suggest this two
> lines of code should be removed.
>
> Thanks in advanced.
>
> Vic
>
> diff --git a/src/gallium/drivers/r600/r600_texture.c
> b/src/gallium/drivers/r600/r600_texture.c
> index 6de3d6a..536f88f 100644
> --- a/src/gallium/drivers/r600/r600_texture.c
> +++ b/src/gallium/drivers/r600/r600_texture.c
> @@ -622,9 +622,6 @@ struct pipe_transfer* r600_texture_get_transfer(struct
> pipe_context *ctx,
>                 use_staging_texture = TRUE;
>         }
>
> -       if ((usage & PIPE_TRANSFER_READ) && u_box_volume(box) > 1024)
> -               use_staging_texture = TRUE;
> -
>         /* Use a staging texture for uploads if the underlying BO is busy.
> */
>         if (!(usage & PIPE_TRANSFER_READ) &&
>             (rctx->ws->cs_is_buffer_referenced(rctx->cs,
> rtex->resource.cs_buf, RADEON_USAGE_READWRITE) ||
>
> Vic
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