radv: add RADV_DEBUG=nongg_gs for GFX10/GFX10.3

NGG GS doesn't perform well in some cases and having an option to
disable it for performance experiments is very useful.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27518>

docs/envvars.rst

@@ -1278,6 +1278,8 @@ RADV driver environment variables
       disable NGG for GFX10 and GFX10.3
    ``nonggc``
       disable NGG culling on GPUs where it's enabled by default (GFX10.3 only).
+   ``nongg_gs``
+      disable NGG GS for GFX10 and GFX10.3
    ``nort``
       skip executing vkCmdTraceRays and ray queries (RT extensions will still be
       advertised)

src/amd/vulkan/radv_debug.h

@@ -72,6 +72,7 @@ enum {
    RADV_DEBUG_VIDEO_ARRAY_PATH = 1ull << 41,
    RADV_DEBUG_NO_RT = 1ull << 42,
    RADV_DEBUG_NO_MESH_SHADER = 1ull << 43,
+   RADV_DEBUG_NO_NGG_GS = 1ull << 44,
 };
 
 enum {

src/amd/vulkan/radv_instance.c

@@ -77,6 +77,7 @@ static const struct debug_control radv_debug_options[] = {{"nofastclears", RADV_
                                                           {"videoarraypath", RADV_DEBUG_VIDEO_ARRAY_PATH},
                                                           {"nort", RADV_DEBUG_NO_RT},
                                                           {"nomeshshader", RADV_DEBUG_NO_MESH_SHADER},
+                                                          {"nongg_gs", RADV_DEBUG_NO_NGG_GS},
                                                           {NULL, 0}};
 
 const char *

src/amd/vulkan/radv_pipeline_graphics.c

@@ -2026,8 +2026,12 @@ radv_fill_shader_info_ngg(struct radv_device *device, struct radv_shader_stage *
          }
       }
 
-      if (last_vgt_stage && last_vgt_stage->nir->xfb_info) {
+      if ((last_vgt_stage && last_vgt_stage->nir->xfb_info) ||
-         /* Disable NGG because GFX10/GFX10.3 don't support NGG streamout. */
+          ((device->instance->debug_flags & RADV_DEBUG_NO_NGG_GS) && stages[MESA_SHADER_GEOMETRY].nir)) {
+         /* NGG needs to be disabled on GFX10/GFX10.3 when:
+          * - streamout is used because NGG streamout isn't supported
+          * - NGG GS is explictly disabled to workaround performance issues
+          */
          if (stages[MESA_SHADER_TESS_EVAL].nir)
             stages[MESA_SHADER_TESS_EVAL].info.is_ngg = false;
          else