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tu/a7xx: Bypass invoking empty FS for D/S-only draw calls

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It is important to get D/S only draw calls to bypass invoking
the fragment shader. The public documentation for Adreno states:
  "Hint the driver to engage Fast-Z by using an empty fragment
   shader and disabling frame buffer write masks for renderpasses
   that modify Z values only."
  "The GPU has a special mode that writes Z-only pixels at twice
   the normal rate."

We are promised a big performance improvement in this case.

Signed-off-by: Danylo Piliaiev <dpiliaiev@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33735>
This commit is contained in:
Danylo Piliaiev 2025-02-25 13:41:26 +01:00
parent b0a98d3b13
commit ace933455c
3 changed files with 22 additions and 3 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

4
src/freedreno/vulkan/tu_cmd_buffer.cc
View file

@ -5803,6 +5803,10 @@ tu6_build_depth_plane_z_mode(struct tu_cmd_buffer *cmd, struct tu_cs *cs)
if (fs->variant->fs.early_fragment_tests)
zmode = A6XX_EARLY_Z;
/* FS bypass requires early Z */
if (fs->variant->empty)
zmode = A6XX_EARLY_Z;
tu_cs_emit_pkt4(cs, REG_A6XX_GRAS_SU_DEPTH_PLANE_CNTL, 1);
tu_cs_emit(cs, A6XX_GRAS_SU_DEPTH_PLANE_CNTL_Z_MODE(zmode));

19
src/freedreno/vulkan/tu_pipeline.cc
View file

@ -3124,6 +3124,7 @@ uint32_t
tu6_rast_size(struct tu_device *dev,
const struct vk_rasterization_state *rs,
const struct vk_viewport_state *vp,
const struct tu_shader *fs,
bool multiview,
bool per_view_viewport)
{
@ -3139,6 +3140,7 @@ void
tu6_emit_rast(struct tu_cs *cs,
const struct vk_rasterization_state *rs,
const struct vk_viewport_state *vp,
const struct tu_shader *fs,
bool multiview,
bool per_view_viewport)
{
@ -3195,12 +3197,22 @@ tu6_emit_rast(struct tu_cs *cs,
bool conservative_ras_en =
rs->conservative_mode ==
VK_CONSERVATIVE_RASTERIZATION_MODE_OVERESTIMATE_EXT;
/* This is important to get D/S only draw calls to bypass invoking
* the fragment shader. The public documentation for Adreno states:
* "Hint the driver to engage Fast-Z by using an empty fragment
* shader and disabling frame buffer write masks for renderpasses
* that modify Z values only."
* "The GPU has a special mode that writes Z-only pixels at twice
* the normal rate."
*/
bool disable_fs = !fs || fs->variant->empty;
tu_cs_emit_regs(cs, RB_RENDER_CNTL(CHIP,
.fs_disable = disable_fs,
.raster_mode = TYPE_TILED,
.raster_direction = LR_TB,
.conservativerasen = conservative_ras_en));
tu_cs_emit_regs(cs, A7XX_GRAS_SU_RENDER_CNTL());
tu_cs_emit_regs(cs, A7XX_GRAS_SU_RENDER_CNTL(.fs_disable = disable_fs));
tu_cs_emit_regs(cs,
A6XX_PC_DGEN_SU_CONSERVATIVE_RAS_CNTL(conservative_ras_en));
@ -3637,6 +3649,7 @@ tu_pipeline_builder_emit_state(struct tu_pipeline_builder *builder,
pipeline_contains_all_shader_state(pipeline),
builder->graphics_state.rs,
builder->graphics_state.vp,
pipeline->shaders[MESA_SHADER_FRAGMENT],
builder->graphics_state.rp->view_mask != 0,
pipeline->program.per_view_viewport);
DRAW_STATE_COND(ds, TU_DYNAMIC_STATE_DS,
@ -3868,9 +3881,11 @@ tu_emit_draw_state(struct tu_cmd_buffer *cmd)
}
DRAW_STATE_COND(rast, TU_DYNAMIC_STATE_RAST,
cmd->state.dirty & (TU_CMD_DIRTY_SUBPASS |
TU_CMD_DIRTY_PER_VIEW_VIEWPORT),
TU_CMD_DIRTY_PER_VIEW_VIEWPORT |
TU_CMD_DIRTY_FS),
&cmd->vk.dynamic_graphics_state.rs,
&cmd->vk.dynamic_graphics_state.vp,
cmd->state.shaders[MESA_SHADER_FRAGMENT],
cmd->state.vk_rp.view_mask != 0,
cmd->state.per_view_viewport);
DRAW_STATE_COND(ds, TU_DYNAMIC_STATE_DS,

2
src/freedreno/vulkan/tu_shader.cc
View file

@ -2079,7 +2079,7 @@ tu6_emit_fs(struct tu_cs *cs,
if (CHIP >= A7XX) {
tu_cs_emit_regs(cs, A6XX_GRAS_UNKNOWN_8110(0x2));
tu_cs_emit_regs(cs, A7XX_HLSQ_FS_UNKNOWN_A9AA(.fs_disable = false));
tu_cs_emit_regs(cs, A7XX_HLSQ_FS_UNKNOWN_A9AA(.fs_disable = !fs || fs->empty));
}
if (fs) {