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[Perf] (DirectVulkan): reuse descriptor set across draws with identical bindings

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BindProgramUniformBuffers rebuilt a fresh descriptor set and called
vkUpdateDescriptorSets on every draw, even when consecutive draws bound the exact
same textures/samplers/buffers (common in MC: many draws share a program + atlas).
Now, after resolving the bindings (still needed for the UBO dynamic offset),
compute a cheap word-wise signature of the resolved descriptor content + layout;
when it matches the previous draw, reuse that descriptor set and skip
AcquireDescriptorSet + vkUpdateDescriptorSets - only the bind-time dynamic offsets
differ.

Correct by construction: bindings are re-resolved every draw so the signature
always reflects current state and reuse only happens on an exact match; the reused
set is never re-acquired within a frame (the acquire cursor only advances); the
descriptor set layout is in the signature so reuse never crosses programs; the
cache resets each frame in BeginFrame when the frame's sets are recycled; sampler
overrides (blits) bypass and invalidate it. The signature hashes 64-bit words (the
Vk*Info payloads are 8-byte-multiple sized and value-initialized) so its own
per-draw cost stays small.

Device-verified on Adreno 830 (MC 26.3-snapshot3, optimized -O2 Magma): rendering
correct, no validation errors. Render-thread wall-clock profile:
BindProgramUniformBuffers 22.85% -> 19.82% (vkUpdateDescriptorSets ~5% dropped below
noise; word-wise signature adds ~0.6% self), SetupDraw 62% -> 60%.
This commit is contained in:
swung0x48
2026-07-12 01:55:31 -04:00
parent b253df881d
commit 009e37ec6f
2 changed files with 71 additions and 8 deletions
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MobileGL/MG_Backend/DirectVulkan/Renderer/UniformManager.h
+9
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@@ -121,6 +121,15 @@ namespace MobileGL::MG_Backend::DirectVulkan {
Vector<VkDescriptorImageInfo> m_imageInfosScratch;
Vector<VkBufferView> m_texelBufferViewsScratch;
Vector<Uint32> m_dynamicOffsetsScratch;
// Descriptor-set reuse across consecutive draws (see BindProgramUniformBuffers).
// When a draw's resolved descriptor content is byte-identical to the previous
// draw's, reuse the same VkDescriptorSet and skip AcquireDescriptorSet +
// vkUpdateDescriptorSets - only the bind-time dynamic offsets differ. Reset each
// frame in BeginFrame because the frame's descriptor sets are recycled there.
VkDescriptorSet m_lastBoundDescriptorSet = VK_NULL_HANDLE;
Uint64 m_lastDescriptorSignature = 0;
Bool m_hasLastDescriptor = false;
};
} // namespace MobileGL::MG_Backend::DirectVulkan