MobileGL/docs/archive/notes/p5e/reports/mv-v1.md

mv-v1 — the multi-draw path stops reading the frontend VAO

Branch p5e/mv, head 5c777b49, base 7c6f6886, tree ~/w7/p5e-mv. Two commits: 98ea1604 (the migration) and 5c777b49 (the tier lanes, added on the coordinator's ruling — §6b). integration-split is now 176, not 116; integration-gpu 1354, not 1294.

1 Site inventory — what I actually found in MultiDraw.cpp

The task named MultiDraw.cpp:93-98 and its caller. The read is one helper, but it had five call sites, not the two the Kimi audit's row 128 lists (MD:909, MD:930):

line (base)	caller	what it asked of the bound VAO
413	RunIndirect	presence only (if (!indexBuffer) return false;)
505	RunRebasedDrawElements	presence + SyncPersistentMappedRange / SyncGpuWrites / MappedData() / GetSize()
553	RunRebasedDrawElements	BoundIndexBufferId() — the restore name
717/724	FlattenWithCompute	presence + EnsureBufferResource(...)->id + GetSize()
909	DrawElementsBatch	presence (BoundIndexBuffer() != nullptr)
930	DrawElementsBatch	BoundIndexBufferId() — the restore name

So the helper answers exactly three questions: is one bound, what GL name is bound (and how big is its store), give me its bytes on the CPU. That is the shape the migration took.

Audit of the other apply-thread frontend reads in this file (§2 of the task), all left alone: :46 GetPrimitiveRestartIndex() and :52-53 IsCapabilityEnabled(PrimitiveRestart / …FixedIndex) are filled for the draw verbs (no marker at base, none now). :88 GetBufferBindingSlot(BufferTarget::DrawIndirect) in BoundDrawIndirectBufferId() is a latent row and not mine: FieldOwnership.def:78 carries it as BARRIER_PULLED, "P8 (indirect), P9 (readback), P13 (transfer)". It is unreachable in the lane because this driver resolves the ext tier and RunIndirect never runs; forcing MOBILEGL_ESPRYT_MULTIDRAW_MODE=indirect under the strict lane would abort GetBufferBindingSlot@DrawArrays. It retires with P8's indirect row.

2 What changed, per file (commit 98ea1604; the test registration is §6b / 5c777b49)

MobileGL/MG_Backend/DirectGLES/MultiDraw.cpp (+150/-25, the block at :94-250 plus the five call sites at :553, :644-670, :849-862, :1046)

• enum class IndexBufferQuestion { Presence, DriverName, DriverNameAndSize, HostBytes } + struct BoundIndexBufferView { Present, Id, Size, HostBytes } + one resolver, ResolveBoundIndexBuffer(question, entry).
• The four question values are deliberately not nested levels: each is exactly the work its original call site did, in its original order, so the monolith arm issues the same calls in the same sequence (requirement 3). DriverName does not read GetSize() because BoundIndexBufferId never did; HostBytes does not Ensure because RunRebasedDrawElements never did.
• Record arm: MGPipeApplier().IndexBuffer.Res via BufferImpl::ResolveDrawIndexBufferFromRecord (vi's own accessor, not a new one) → EnsureBufferResourceForHandle(nullptr, res)->id for the name, ResourceWidthForHandle(res) for the size, FindBufferResourceForHandle(res)->hostBytes + RequireStagedCoverage for the CPU bytes. No wire row was added. This is the identical set of calls ScopedRestartIndexSubstitution's transport arm (DirectGLES.cpp:8317-8372) already makes for the single-draw restart rewrite, including the HasDefinedContent M-3 rule.
• ResolveSubDrawIndices takes Bool hasIndexBuffer instead of the frontend SharedPtr: presence was the only thing it ever asked of it. FlattenWithCompute asks twice (Presence, then DriverNameAndSize) so the ensure stays behind the IsCaptureSpanOpen() check, where it was.

MobileGL/MG_Backend/DirectGLES/Managers.h (+32 at :1096) and MobileGL/MG_Backend/DirectGLES/DirectGLES.cpp (-25/+4 at :524)

BufferImpl::VertexInputReadsRecords() moved from DirectGLES.cpp:542 to Managers.h, body and rationale unchanged, plus a paragraph saying why. MultiDraw.cpp is a second translation unit on the same draw path and has to select the same arm; the addendum's rule ("state the transport test where you rely on it") is met by a shared definition rather than by a second copy of the conjunction that can drift. This is the only delta to shared code.

Arm selection, against the addendum's checklist

• Decided by BufferImpl::VertexInputReadsRecords() ⇒ Transport != Monolith && VertexInputSubsystemEnabled(). Never by "a handle was noted", never by a null pointer. The null-Res test inside the record arm is "no element buffer bound", the same statement as a null frontend slot on the other arm — and it runs after the arm has already been chosen.
• A missing record on the handle arm is a named refusal, RefuseMissingIndexBufferRecord → Fatal{RoleViolation, "multidraw-index-buffer-arm"}, shaped on RefuseNullFrontendTextureOffTheHandleArm, and entirely under #if MOBILEGL_BUILD_DISAGGREGATED so the pull build gains no call (D-P).
• Nothing passes a null object into a body that can still read one: on the record arm no frontend object is produced at all, and the three answers are values, not pointers into frontend state.

3 Rows of my family — retired / barriered / not found

• Retired: Kimi audit row 128 (MD:909, MD:930, BoundIndexBuffer() / BoundIndexBufferId(), carrier IndexBuffer at AP:620) — retired, and with it the three sites the audit did not list (MD:413, MD:505, MD:717), which are the same helper.
• Left barriered (named, with an owner): BoundDrawIndirectBufferId's GetBufferBindingSlot(DrawIndirect) — P8's indirect row, §1 above.
• Not found: the audit's rows 12/13 (D:6729, D:6768/6777) are the arrays multi-draw and never enter this file, and PipeApplier.cpp:628 collapses drawcount == 1 onto the single-range arm — so the nine entries are exactly "an indexed multi-draw whose record carries NumDraws != 1".

4 Red-once, verbatim

(1) Revert the arm selection. if (false /* P5E-MV-RED1 */ && BufferImpl::VertexInputReadsRecords()), rebuilt, censused. Exactly the nine entries come back, nothing else moves (~/w7/p5e-logs/strict-census-mv/red1/census.tsv: 9 × GetBoundVertexArray@DrawArrays, 7 × GetProgramForDraw@DrawArrays — the seven are other MultiDraw* entries that were already pa's):

[11:41:05] [Linux mgl-srv-apply/FATAL]: MGPipe: Fatal{UnmigratedPipeInput, "GetBoundVertexArray@DrawArrays"} [BARRIER-PULLED, MOBILEGL_IPC_STRICT_ERRORS=1, retires in P5e (Espryt unbarriered), P7 (Magma)]

(2) Make the record lookup miss on the handle arm. resource = nullptr after each by-handle lookup, MultiDrawScenario.PlainBatchMatchesUnrolledDraws, split-lane env, MOBILEGL_LOG_FILE_PATH set (~/w7/p5e-logs/strict-census-mv/red2/). Both entry points abort by name, rc=134:

[11:41:59] [Linux mgl-srv-apply/FATAL]: MGPipe: Fatal{RoleViolation, "multidraw-index-buffer-arm"} - RunRebasedDrawElements found no backend resource for the index buffer {2, 0} this batch's record named. The index buffer of this family is MGPipeApplier().IndexBuffer.Res (CONTRACT-P5E §5.1) and the arm is selected by Transport != Monolith AND the vertex-input subsystem bit (§5.8, ID-81); falling back to the frontend VAO's element slot here would draw this multi-draw from whatever the CLIENT has bound now
[11:41:59] [Linux mgl-srv-apply/FATAL]: MGPipe: Fatal{RoleViolation, "multidraw-index-buffer-arm"} - FlattenWithCompute found no backend resource for the index buffer {2, 0} this batch's record named. The index buffer of this family is MGPipeApplier().IndexBuffer.Res (CONTRACT-P5E §5.1) and the arm is selected by Transport != Monolith AND the vertex-input subsystem bit (§5.8, ID-81); falling back to the frontend VAO's element slot here would draw this multi-draw from whatever the CLIENT has bound now

The FlattenWithCompute line does double duty: FlattenWithCompute returns before any of this unless ResolvedTier() == Compute, and Auto never yields Compute. It is therefore the proof that MOBILEGL_ESPRYT_MULTIDRAW_MODE really selects the tier in §6's sweep below.

(3) Both put back. git diff empty against 98ea1604; rebuild rc=0; the nine entries are back on pa's row (~/w7/p5e-logs/strict-census-mv/green/census.tsv), isplit 116/116.

5 Strict marker census, before and after

~/w7/p5e-logs/strict-census/census2.tsv (base) vs ~/w7/p5e-logs/strict-census-mv/census2.tsv (head). Copied to a per-slug directory so pa's reads of the shared one are undisturbed.

marker	before	after	owner
GetProgramForDraw@DrawArrays	61	70	pa
GetFramebufferBindingSlot@ReadPixels	21	21	allowlist (readback)
GetBoundVertexArray@DrawArrays	9	0	mv — retired
GetProgramForDispatch@DispatchCompute	7	7	pa
GetTextureObject@CopyImageSubData	6	6	allowlist (P7)
ValidateProgramName@ShaderStorageBlockBinding	2	2	allowlist (P9)
GetTextureUnitObject@CopyTexImage2D	2	2	allowlist (CopyTex)
<no-marker> (census artifact, addendum §4)	1	1	—
total	109	109

The full diff of the two tables is exactly 9 lines out of my row and the same 9 entries into GetProgramForDraw@DrawArrays: MultiDrawElementsBaseVertexPaintsEverySubDraw and the eight MultiDrawScenario cases now get past the index buffer and stop on pa's row instead. No row that is not mine changed count for any other reason, and no new marker appeared. When pa lands, these nine go green with no further work here.

6 Gate

Final numbers, at head 5c777b49 (i.e. with the new lanes):

step	result
build	rc=0
unit	2250/2250
isplit	176/176 (was 116/116; +60 new entries, §6b)
gpu (ID-109)	1354/1354 (was 1294/1294; the same +60)
gens	all seven rc=0; doc citations only the pre-existing CONTRACT-P5.md:524 ambiguity
strict (count)	7/176 (was 7/116): the 9 moved to pa's row, the 60 new ones land on it too
strict (per-entry census)	table in §5, unchanged — no backend source moved after it was taken

6b The tier lanes (coordinator's ruling — done, commit 5c777b49)

Evidence first, because an entry that silently resolves to ext is worse than no entry. I temporarily promoted MultiDraw.cpp's two MGLOG_D tier lines to MGLOG_I (ResolveTierOnce's resolution line and NoteTierExecuted's "first batch executed via tier"), rebuilt, swept, reverted. Every mode resolves to itself on this driver — no fallback:

mode	ResolveTier says	tiers a batch actually executed	cases
ext	ext -> ext	ext	17/17
basevertex	basevertex -> basevertex	basevertex	17/17
multiindirect	multiindirect -> multiindirect	multiindirect	17/17
indirect	indirect -> indirect	indirect	17/17
drawelements	drawelements -> drawelements	drawelements	17/17
compute	compute -> compute	compute + basevertex	17/17

Each line ends (driver supports: ext, basevertex, multiindirect, indirect, drawelements, compute (opt-in)), so no tier is refused here and none is skipped. The compute row executing basevertex as well is ResolveTierForBatch demoting the batch shapes the flattening tier declines by design (strips, primitive restart, per-sub-draw base vertex) — the tier was selected, and three of its cases fell through to the unrolled floor, which is the documented behaviour.

Registered: five blocks in MobileGL/MG_IntegrationTest/CMakeLists.txt:2017-2087, one per tier auto cannot reach, prefix DirectGLES.Split.MultiDrawTier{BaseVertex,MultiIndirect,Indirect,DrawElements,Compute}., labels integration-gpu;integration-split, and MOBILEGL_ESPRYT_MULTIDRAW_MODE pinned as a ctest ENVIRONMENT property (verified on a live entry with ctest -N -V, which prints the full split environment plus MOBILEGL_ESPRYT_MULTIDRAW_MODE=compute). Filter: MultiDrawScenario.*:IndexedDrawFamilyScenario.MultiDraw* minus the client-indices case the d1 block already excludes by name — 12 entries × 5 tiers = 60 new entries, all green.

• ext is deliberately not a sixth block: auto already resolves to it, so the d1 block is the ext lane and a sixth would run it twice. Stated in the block comment so nobody re-adds it.
• The filter is narrowed to the tier-sensitive workload, this file's own stated rule for an armed Split. entry: IndexedDrawFamilyScenario's other five cases are single draws that never enter MultiDrawImpl, so five copies of them would be five copies of the d1 lane. One word in MGL_SPLIT_MULTIDRAW_TIER_FILTER widens it to the whole scenario (+25 entries) if you prefer.
• Harness/SplitLogPaths.cmake.in gains a matching loop: every DirectGLES.Split. entry must own one private log path or SplitLogPaths.PrivateAndDistinct is red — it caught this on my first run, the only thing that failed, and it was the guard doing its job. For these lanes it also repairs addendum §4's blind spot: their third name segment means strict_census2.sh would re-run them without the very pin under test, so their markers are read from build-split/…/split-logs/<entry>.log instead (~/w7/p5e-mv/.p5e/strict-new.sh).
• Strict-lane effect of the 60: all 60 abort on GetProgramForDraw@DrawArrays — pa's existing row, because PrepareForDraw runs before the tier dispatch. No new marker class, mv's row stays at 0. Per-entry table: ~/w7/p5e-logs/strict-census-mv/tiers.tsv.

7 G1 / monolith impact

• Every record-arm line is under #if MOBILEGL_BUILD_DISAGGREGATED. The monolith arm's body is the original text, and the four question values exist so that its call sequence is unchanged too.
• gpu (the Transport == Monolith runtime arm, ID-109) is 1294/1294.
• Finding for the integrator, pre-existing and not mine: the pull flavour (MOBILEGL_PIPE_PUSH=0, MOBILEGL_BUILD_DISAGGREGATED=0) does not compile at 7c6f6886 either. Syntax-checking the touched TUs with the split build's own compile line and the two flavour defines flipped (~/w7/p5e-mv/.p5e/pullcheck.sh): MultiDraw.cpp rc=0, Managers.cpp rc=0, DirectGLES.cpp rc=1 on two identifiers that predate this package — DirectGLES.cpp:5554 calls ComputeShaderStorageBlockBindingSignatureOf, declared only inside #if MOBILEGL_PIPE_PUSH (Managers.h:3154-3160, pg's), and DirectGLES.cpp:6675 declares const Bool keysMatch inside #if MOBILEGL_BUILD_DISAGGREGATED while the : else-arm and the use at :6695 are outside it. Both are verbatim at the base commit (git show 7c6f6886:…DirectGLES.cpp → :5575 and :6696). So G1 for this package is "no new break, and my own TU is clean"; the tree's pull build is already red and nothing in the gate notices.

8 Seams, assumptions, and what I need from the integrator

1. Seam with pa. My nine entries now stop on GetProgramForDraw@DrawArrays. I touched no program row and no file pa works in; my only shared-code edit is VertexInputReadsRecords() moving out of DirectGLES.cpp:524-549 into Managers.h, ~4000 lines from pa's region. If pa also moved something out of that BufferImpl block, that is the one place to check at merge.
2. Assumed from vi/sb: ResolveDrawIndexBufferFromRecord, EnsureBufferResourceForHandle, FindBufferResourceForHandle, ResourceWidthForHandle, RequireStagedCoverage and GLESBufferResource::hostBytes mean on the multi-draw path exactly what they mean in ScopedRestartIndexSubstitution and in SyncNeccessaryBuffers' record arm. Minted nothing.
3. Tier coverage — ruled on, done (§6b). The five unreachable tiers now have gated entries. Two consequences for the merge: integration-split is 176 and integration-gpu 1354, and the strict lane's denominator moves with them (7/176). One judgement call is mine to flag: I narrowed IndexedDrawFamilyScenario to its MultiDraw* cases — one word to widen.
4. Ruling wanted — the pull build. §7. Noted as yours to verify; I have not touched it.
5. Not done, deliberately: BoundDrawIndirectBufferId (§1, P8's row — confirmed out of phase scope); no wire row; no change to the tier ladder, the scratch ring, or the restore semantics at :102-105, which the migration preserves by answering the same GL name from the record.

Scripts used, all under ~/w7/p5e-mv/.p5e/ (gitignored): strict_census_mv.sh (per-slug census, output ~/w7/p5e-logs/strict-census-mv/), census9.sh, red2.sh, tier-sweep.sh, pullcheck.sh, strict-new.sh (markers of the 60 new entries, read from their own lane logs).