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Assets/ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/Resources/CopyStencilBuffer.shader

                 uint2 positionSS = (uint2)input.positionCS.xy;
 
                 // There's no need for atomics as we are always writing the same value.
+                // Note: the GCN tile size is 8x8 pixels.
                 _HTile[positionSS / 8] = STENCILLIGHTINGUSAGE_SPLIT_LIGHTING;
 
                 return float4(STENCILLIGHTINGUSAGE_SPLIT_LIGHTING, 0, 0, 0);

Assets/ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/Resources/SubsurfaceScattering.compute

 void SubsurfaceScattering(uint2 groupId       : SV_GroupID,
                           uint  groupThreadId : SV_GroupThreadID)
 {
+    // Note: any factor of 64 is a suitable wave size for our algorithm.
     uint waveIndex = groupThreadId / 64;
     uint laneIndex = groupThreadId % 64;
     uint quadIndex = laneIndex / 4;