[Mesa-dev] [PATCH 3/3] radv: implement a fast prefetch path for the vertex stage

[Bas Nieuwenhuizen]

Reviewed-by: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>

for the series.

On Wed, Apr 4, 2018 at 12:12 PM, Samuel Pitoiset
<samuel.pitoiset at gmail.com> wrote:
> This allows to start draws as soon as possible.
>
> Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
> ---
>  src/amd/vulkan/radv_cmd_buffer.c | 40 ++++++++++++++++++++++++++++++----------
>  1 file changed, 30 insertions(+), 10 deletions(-)
>
> diff --git a/src/amd/vulkan/radv_cmd_buffer.c b/src/amd/vulkan/radv_cmd_buffer.c
> index 393d9ba4f4..0e59f99799 100644
> --- a/src/amd/vulkan/radv_cmd_buffer.c
> +++ b/src/amd/vulkan/radv_cmd_buffer.c
> @@ -640,39 +640,48 @@ radv_emit_shader_prefetch(struct radv_cmd_buffer *cmd_buffer,
>
>  static void
>  radv_emit_prefetch_L2(struct radv_cmd_buffer *cmd_buffer,
> -                     struct radv_pipeline *pipeline)
> +                     struct radv_pipeline *pipeline,
> +                     bool vertex_stage_only)
>  {
>         struct radv_cmd_state *state = &cmd_buffer->state;
> +       uint32_t mask = state->prefetch_L2_mask;
>
>         if (cmd_buffer->device->physical_device->rad_info.chip_class < CIK)
>                 return;
>
> -       if (state->prefetch_L2_mask & RADV_PREFETCH_VS)
> +       if (vertex_stage_only) {
> +               /* Fast prefetch path for starting draws as soon as possible.
> +                */
> +               mask = state->prefetch_L2_mask & (RADV_PREFETCH_VS |
> +                                                 RADV_PREFETCH_VBO_DESCRIPTORS);
> +       }
> +
> +       if (mask & RADV_PREFETCH_VS)
>                 radv_emit_shader_prefetch(cmd_buffer,
>                                           pipeline->shaders[MESA_SHADER_VERTEX]);
>
> -       if (state->prefetch_L2_mask & RADV_PREFETCH_VBO_DESCRIPTORS)
> +       if (mask & RADV_PREFETCH_VBO_DESCRIPTORS)
>                 si_cp_dma_prefetch(cmd_buffer, state->vb_va, state->vb_size);
>
> -       if (state->prefetch_L2_mask & RADV_PREFETCH_TCS)
> +       if (mask & RADV_PREFETCH_TCS)
>                 radv_emit_shader_prefetch(cmd_buffer,
>                                           pipeline->shaders[MESA_SHADER_TESS_CTRL]);
>
> -       if (state->prefetch_L2_mask & RADV_PREFETCH_TES)
> +       if (mask & RADV_PREFETCH_TES)
>                 radv_emit_shader_prefetch(cmd_buffer,
>                                           pipeline->shaders[MESA_SHADER_TESS_EVAL]);
>
> -       if (state->prefetch_L2_mask & RADV_PREFETCH_GS) {
> +       if (mask & RADV_PREFETCH_GS) {
>                 radv_emit_shader_prefetch(cmd_buffer,
>                                           pipeline->shaders[MESA_SHADER_GEOMETRY]);
>                 radv_emit_shader_prefetch(cmd_buffer, pipeline->gs_copy_shader);
>         }
>
> -       if (state->prefetch_L2_mask & RADV_PREFETCH_PS)
> +       if (mask & RADV_PREFETCH_PS)
>                 radv_emit_shader_prefetch(cmd_buffer,
>                                           pipeline->shaders[MESA_SHADER_FRAGMENT]);
>
> -       state->prefetch_L2_mask = 0;
> +       state->prefetch_L2_mask &= ~mask;
>  }
>
>  static void
> @@ -3042,7 +3051,7 @@ radv_draw(struct radv_cmd_buffer *cmd_buffer,
>                  */
>                 if (cmd_buffer->state.prefetch_L2_mask) {
>                         radv_emit_prefetch_L2(cmd_buffer,
> -                                             cmd_buffer->state.pipeline);
> +                                             cmd_buffer->state.pipeline, false);
>                 }
>         } else {
>                 /* If we don't wait for idle, start prefetches first, then set
> @@ -3051,8 +3060,11 @@ radv_draw(struct radv_cmd_buffer *cmd_buffer,
>                 si_emit_cache_flush(cmd_buffer);
>
>                 if (cmd_buffer->state.prefetch_L2_mask) {
> +                       /* Only prefetch the vertex shader and VBO descriptors
> +                        * in order to start the draw as soon as possible.
> +                        */
>                         radv_emit_prefetch_L2(cmd_buffer,
> -                                             cmd_buffer->state.pipeline);
> +                                             cmd_buffer->state.pipeline, true);
>                 }
>
>                 if (!radv_upload_graphics_shader_descriptors(cmd_buffer, pipeline_is_dirty))
> @@ -3060,6 +3072,14 @@ radv_draw(struct radv_cmd_buffer *cmd_buffer,
>
>                 radv_emit_all_graphics_states(cmd_buffer, info);
>                 radv_emit_draw_packets(cmd_buffer, info);
> +
> +               /* Prefetch the remaining shaders after the draw has been
> +                * started.
> +                */
> +               if (cmd_buffer->state.prefetch_L2_mask) {
> +                       radv_emit_prefetch_L2(cmd_buffer,
> +                                             cmd_buffer->state.pipeline, false);
> +               }
>         }
>
>         assert(cmd_buffer->cs->cdw <= cdw_max);
> --
> 2.16.3
>