Two per-draw costs from the round-10 profiles. A per-program sampled-set
epoch inside UniformManager skips the per-binding descriptor proof walk
when no texture or sampler API ran since that program's previous draw -
the mc_sampler_churn/mc_tex_param pattern. The pass-switch path stops
re-deriving render-pass state that its own value hash already pins.
Load-gated 6-round order-alternating A/B (medians): magma tex_param
-13.3%, pass_switch -10.9%, state_toggle -5.4%; espryt untouched and
unmoved. The two matrix flags (sodium +7.5%, tex_stream +6.2%) reversed
under 10-pair isolated alternating re-runs (-5.5% and +2.5%) - the same
position-bias artifact every previous round's flags showed. Unit tests
421/421; retrace subset and the 52-entry integration suite pass.
Landing note: this diff was authored by a round-10 agent whose session
died before adjudication; the A/B data survived (r10bmag_ab_raw.csv)
and the flags were adjudicated before landing. Its relink also exposed
the pre-existing exit-teardown SIGSEGV fixed in the previous commit.
TrySetupDrawFastPath declined on its VAO pointer check for every draw of
a 512-VAO cycle - the Blaze3D chunk-render shape - so the fast path was
dead exactly where it mattered: full SetupDraw, per-draw
ResolveSamplerDescriptor, SyncTextureAndGetDescriptor and render-pass
re-fetch, for draws whose only change was the VAO.
Three fixes. A moved VAO now re-runs only the vertex-input pre-flight
and re-resolves the pipeline instead of declining to the full path. That
resolution probes the value-keyed pipeline memo directly off a cached
pipeline-state hash and snapshot render-pass hash, skipping
GetOrCreateRenderPass and its GetPendingRenderbufferClear probes per
draw; a stale cached hash can only miss, never false-hit. And when the
sampler-descriptor hint holds and the program's single dynamic UBO
re-resolves to the same VkBuffer and range - only the dynamic offset
moved, the per-draw glUniform case - the descriptor walk collapses to
one offset recompute and a vkCmdBindDescriptorSets of the same recorded
set with new pDynamicOffsets. The rebind memo is invalidated at
BeginFrame, layout destruction and override walks; the program lifetime
id never repeats, and per-frame descriptor sets are never rewritten
within their frame.
mc_vanilla_draw -36.9% (1260 -> 795 ns/op, 4.6x native to 3.4x),
sodium_multidraw -18.0%, state_toggle -14.9%, sampler_churn -7.8%,
use_program -7.7%, ubo_range -7.3%, tex_param -7.3%. All nine cases on
both backends, interleaved A/B; no attributable regression. Unit tests
421/421.
Two per-draw churn costs, one cause each.
A blend toggle switched pipelines through a memo keyed on a monotonic
pipeline-state version - which never repeats, so flipping GL_BLEND off and back
on produced a "new" key both times, forced the full SetupDraw and rebuilt the
whole pipeline payload for a pipeline the cache already held. The memo now keys
on a value hash of the pipeline-relevant fixed-function state, recomputed only
when the state version moved, and the consecutive-draw fast path re-resolves
just the pipeline through it when nothing but render state changed. Blaze3D
brackets every batch with exactly this toggle; mc_state_toggle drops 36%
(6629 -> 4230 ns/op, 4.8x native to 3.7x).
The sampler-churn cost had the same shape as the Espryt side fixed separately:
glBindSampler bumps the frontend texture-bind generation even when it re-binds
the sampler the unit already holds, so the per-draw fast path died every draw.
The fast path now proves each binding's descriptor inputs unchanged - texture
and sampler lifetime ids, parameter and content sums, the sampling-resolution
generation, image epochs and exact layouts - and reuses the binding's cached
VkDescriptorImageInfo instead of re-running the resolve chain.
mc_sampler_churn drops 30% (1597 -> 1125), and the proof machinery pays for
itself on the uniform-range case too (-17%).
mc_tex_param stays where it is on this backend deliberately: profiling shows its
remaining cost is frontend validation with zero backend work, unreachable from
Renderer/.
All nine cases measured on both backends, interleaved A/B, no case worse than
noise. Unit tests 421/421.
A per-draw CPU profile of a real Minecraft frame (perf on the render thread,
which sits at 100% of one core on both backends) said the deficit is translation
overhead, not the GPU, and named where it goes. This removes the largest items
it found, on both backends and in the shared frontend they both feed.
The single biggest one was not translation at all: IsBackendContextCurrentOnThisThread
called eglGetCurrentContext on every invocation, and glvnd answers that with a
getpid() fork check - a real syscall. The predicate sits two and three deep in
every draw (the deferred-release drain, the global-UBO ring availability check,
and the ring allocation), so it accounted for 16.3% of the render thread. EGL is
still the ground truth, but re-verifying it once per thread per frame catches an
external migration at the next frame boundary rather than the next call, which
recovers the same bookkeeping.
Texture uploads now carry a dirty region instead of a per-level flag. Minecraft
animates atlas sprites with 16x16 glTexSubImage2D calls into a 1024x512 atlas
and respecifies the lightmap every frame; a per-level flag turned each of those
into a full-level re-upload - about 3.6 MB a frame of texels nobody changed.
MipmapStorage accumulates the written box, Espryt uploads it with
UNPACK_ROW_LENGTH striding into the level shadow, and Magma stages just that box.
The box is a union, not a range list: repeated writes to one level widen it and
it degrades to exactly the old whole-level upload, which is the honest worst case.
glBufferData(NULL) is the orphaning idiom, and the backend was answering it by
uploading the stale CPU shadow - turning a rename the driver does for free into
a full synchronized upload. BufferObject now records that a NULL respecify leaves
the store undefined, and the upload is skipped until content is actually written.
The rest are smaller and of a kind: the deferred-release queue is probed without
taking its mutex, the UBO ring waits on the frame fence that frees the space it
needs instead of draining the whole pipeline with glFinish at the size cap, VAO
binds go through a shadow so a draw's second bind of the same object does not
reach the driver, the per-draw clean-texture probe short-circuits on the content
version before rebuilding shape info, glUniform drops byte-identical writes
(which otherwise dirty the whole UBO for the next draw), re-binding the texture
or VAO a slot already holds no longer bumps the generation counters a backend
fast path is keyed on, and the texture validators stopped taking shared_ptr by
value.
On Magma: descriptor-set reuse keeps four entries instead of one, because draws
alternating between two programs - the chunk/entity ping-pong - thrashed a single
slot into a full re-allocate and re-write every draw; a DynamicDraw buffer whose
contents survive two frame boundaries is promoted to resident storage instead of
being re-copied into the per-frame arena forever; and sampled-read barriers name
only the shader stages whose device feature is enabled, which also removes a
latent VUID violation (ALL_GRAPHICS names geometry and tessellation stages a
device need not have).
Measured with the Minecraft rig (render distance 32, p50 fps, same machine,
single sample each): vanilla 1.21.1 Espryt 10.8 -> 36.3 and Magma 31.3 -> 44.6;
26.2 snapshot Magma 114.5 -> 210.5. Fabric+Sodium moved inside noise on Magma
(854 -> 766) with the native baseline itself moving 838 -> 1031 between the two
sessions, so treat that cell as unresolved rather than a regression measured.
Unit tests 421/421. The CTS A/B was not run: these numbers and the test suite are
the whole of the evidence, and a conformance regression would not have been
caught here.
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%.
- Memoize the program content hash on ProgramObject (keyed by the backend
state version + compile flags; relinking and binding changes invalidate
it) and the vertex-input hash on VertexArrayObject (keyed by a new
aggregate config version bumped by every attribute mutation). Full-SPIRV
XXH64 hashing fell from 13.7% to 1.4% of the render thread.
- ProgramObject also gains a link version and a global-UBO content version
(bumped by uniform writes and on relink, wrap-safe around the backends'
"never uploaded" sentinel) for backends to gate uploads and link caches.
- Reuse member scratch vectors in SetupDraw, UploadAndBindVertexBuffers,
GetOrCreatePipeline and BindProgramUniformBuffers instead of allocating
per draw (~12% of render-thread time was in the allocator).
- Replace hot-path dynamic_cast with AsMipmapTexture (storage-type tag +
static_cast); TextureObjectMipmap is the only Mipmap-tagged branch.
- Register/prune texture aliases only when a new (texture, lifetimeId)
identity appears instead of scanning the entire alive map on every
sampled-texture sync.
- Make the fallback VkPresentModeKHR log strings report the actual mode.
Vanilla render-thread share of libMobileGL dropped from 48% to 35% on
DirectVulkan (simpleperf, Adreno 830).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
- Support cube map face uploads with cube-compatible images and per-face array layers
- Add uniform texel buffer descriptor support for samplerBuffer bindings
- Cache transient vertex/index buffer uploads per frame to avoid VMA allocation failures
swung0x48
