[Mesa-dev] [PATCH 3/4] anv/cmd_buffer: Flush the VF cache at the top of all primaries

[Lionel Landwerlin]

On 31/03/17 16:17, Jason Ekstrand wrote:
> Cc: "13.0 17.0" <mesa-stable at lists.freedesktop.org>
> ---
>   src/intel/vulkan/genX_cmd_buffer.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
> diff --git a/src/intel/vulkan/genX_cmd_buffer.c b/src/intel/vulkan/genX_cmd_buffer.c
> index 1ce549a..b5297f4 100644
> --- a/src/intel/vulkan/genX_cmd_buffer.c
> +++ b/src/intel/vulkan/genX_cmd_buffer.c
> @@ -597,6 +597,18 @@ genX(BeginCommandBuffer)(
>   
>      genX(cmd_buffer_emit_state_base_address)(cmd_buffer);
>   
> +   /* We sometimes store vertex data in the dynamic state buffer for blorp
> +    * operations and our dynamic state stream may re-use data from previous
> +    * command buffers.  In order to prevent stale cache data, we flush the VF
> +    * cache.  We could do this on every blorp call but that's not really
> +    * needed as all of the data will get written by the CPU prior to the GPU
> +    * executing anything.  The chances are fairly high that they will use
> +    * blorp at least once per primary command buffer so it shouldn't be
> +    * wasted.
> +    */

It took me some time to understand why this is just needed for primary 
buffers.
If I had to come up with a comment, this is how I would put it :

Lifecycles of primary & secondary buffers are tied together when 
CmdExecuteCommands() records commands of the later into the former.
Once recorded into a primary command buffer the secondary command 
buffers cannot be destroyed/reset before the primary is.
Meaning none of the dynamic state addresses used in either buffer cannot 
be reused before primary is destroyed/reset.
As a result the only point at which we can get stale data in the VF 
cache is at the beginning of the primary buffer.

If that matches your understanding, this is :

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>

> +   if (cmd_buffer->level == VK_COMMAND_BUFFER_LEVEL_PRIMARY)
> +      cmd_buffer->state.pending_pipe_bits |= ANV_PIPE_VF_CACHE_INVALIDATE_BIT;
> +
>      VkResult result = VK_SUCCESS;
>      if (cmd_buffer->usage_flags &
>          VK_COMMAND_BUFFER_USAGE_RENDER_PASS_CONTINUE_BIT) {