[Mesa-dev] [PATCH 1/2] anv/cmd_buffer: Don't temporarily enable CCS_E within a render pass

[Jason Ekstrand]

On Mon, Jan 23, 2017 at 4:55 PM, Nanley Chery <nanleychery at gmail.com> wrote:

> Compressing a render target and decompressing it in the same
> single-subpass render pass may waste bandwidth. While this may be
> beneficial in some circumstances, it does not help in all.
>
> Cc: "13.0 17.0" <mesa-stable at lists.freedesktop.org>
>

This doesn't really fix a bug...  I guess you can consider it a perf bug
but it's not going to cause apps to fail.  I think I'm ok with pulling it
back to 17.0 but let's leave 13.0 alone.


> Signed-off-by: Nanley Chery <nanley.g.chery at intel.com>
> ---
>  src/intel/vulkan/genX_cmd_buffer.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/src/intel/vulkan/genX_cmd_buffer.c
> b/src/intel/vulkan/genX_cmd_buffer.c
> index a22fb2b6fb..9cde6896bb 100644
> --- a/src/intel/vulkan/genX_cmd_buffer.c
> +++ b/src/intel/vulkan/genX_cmd_buffer.c
> @@ -265,8 +265,10 @@ color_attachment_compute_aux_usage(struct anv_device
> *device,
>        att_state->fast_clear = false;
>     }
>
> -   if (isl_format_supports_lossless_compression(&device->info,
> -                                                iview->isl.format)) {
> +   /* TODO: Consider using a heuristic to determine if temporarily
> enabling
> +    * CCS_E for this image view would be beneficial.
> +    */
>

Maybe we should update this comment a bit:

While fast-clear resolves and partial resolves are fairly cheap in the case
where you render to most of the pixels, full resolves are not because they
potentially involve reading and writing the entire framebuffer.  If we
can't texture with CCS_E, we should leave it off and limit ourselves to
fast clears.

Also... This doesn't do quite what you think it does.  It shuts off fast
clears entirely on Sky Lake if we can't texture from CCS_E.  We need to add
some code above to do

if (GEN_GEN >= 9 && !isl_format_supports_lossless_compression(...))
   att_state->fast_clear = false;

And then remove the GEN_GEN >= 9 case below.  Maybe we want to do the code
shuffling as a refactor patch and put this patch on top of it?


> +   if (iview->image->aux_usage == ISL_AUX_USAGE_CCS_E) {
>        att_state->aux_usage = ISL_AUX_USAGE_CCS_E;
>        att_state->input_aux_usage = ISL_AUX_USAGE_CCS_E;
>     } else if (att_state->fast_clear) {
> --
> 2.11.0
>
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