host_build_graph: record DSv4's 43 layers as seven Graph Definitions - #1936
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📝 WalkthroughWalkthroughThe change increases recorder-pool prewarming, relaxes release-build boundary rejection in ChangesGraph Definition updates
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: ⚪ Minimal · up to The PR changes graph decomposition and recorder prewarming to reduce host submissions; the only remaining issue is a localized documentation-formatting fix with no product or runtime impact. No actionable merge-blocking risk remains. Possibly related PRs
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In `@docs/investigations/2026-08-hbg-graph-block-decomposition.md`:
- Line 143: Update the sentence mentioning `#1929` so it is not parsed as a
Markdown heading, by prefixing the reference with “PR” or reflowing the sentence
to keep the line as paragraph text.
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docs/investigations/2026-08-hbg-graph-block-decomposition.mddocs/investigations/README.mdexamples/a2a3/host_build_graph/deepseek_v4_flash_decode/README.mdexamples/a2a3/host_build_graph/deepseek_v4_flash_decode/kernels/orchestration/decode_fwd_graph.cppexamples/a2a3/host_build_graph/deepseek_v4_flash_decode/test_deepseek_v4_flash_decode.pysrc/a2a3/runtime/host_build_graph/orchestration/pto_orchestration_api.hsrc/a2a3/runtime/host_build_graph/runtime/orchestrator_core/pto_orchestrator.cppsrc/a5/runtime/host_build_graph/orchestration/pto_orchestration_api.hsrc/a5/runtime/host_build_graph/runtime/orchestrator_core/pto_orchestrator.cppsrc/common/host_build_graph/docs/GRAPH_EXECUTION.mdtests/ut/cpp/common/test_hbg_graph_async_submit.cpp
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`deepseek_v4_flash_decode` submitted 1131 tasks from the submitting thread, so
recording had almost nothing to overlap with: every kernel the submitter enqueued
itself was a kernel no recording thread could be building at the same time.
Cutting the whole forward pass into Graph blocks leaves the submitter 129
submissions and moves the rest onto the recording threads.
Seven Definitions cover every layer:
- `csa_attn_block` (50 nodes) / `csa_moe_block` (32) and `hca_attn_block` (35) /
`hca_moe_block` (31) -- the decoder loop's two alternating layer shapes, layers
2..41, plus layer 42 replaying `csa_attn_block` and `hca_moe_block`.
- `swa_attn_block` (28) -- the two peeled sliding-window attentions of layers 0
and 1. Their nodes are pairwise alpha-equivalent, so layer 1 replays what layer
0 recorded.
- `hash_moe_l0_block` (31) / `hash_moe_l1_block` (31) -- the peeled MoE scopes.
These cannot share a Definition: `dispatch_wait` folds the MoE epoch in as a
constant (32 at layer 0, 64 at layer 1) where the loop's variants take it as a
scalar.
The kernels, their order, and their dependencies are unchanged; only where the
host builds them moves.
Two costs on the recorder side were large enough to eat the win at this
Definition count.
`graph_prepare` re-derived a boundary match it was already handed. It receives
the handle of the recording that `graph_begin` created from the very boundary
being prepared, so that recording cannot carry a different boundary, yet
`graph_recording_boundary_matches` compared up to 128 ChipTensor descriptors a
second time -- 32-46 us per recording, paid on the recording thread before its
first node, which is precisely the start-up latency this path exists to keep
short. It becomes a `debug_assert`, so a boundary that ever stopped matching
still trips in a debug build, and prepare drops to 13-35 us. The search-based
caller at the cache-lookup site keeps its real check: there the boundary is what
identifies the recording, not something already known.
The recorder pool prewarmed four workers, and growing it happens inside `start()`
on the submitting thread, so seven Definitions paid `pthread_create` in the middle
of the submission burst: 170 us and 98 us gaps between Graph submissions,
identified as three and one thread creations by annotating each gap with the
recording lanes whose first record falls inside it. Prewarming eight covers a
forward pass cut into up to eight Definitions; the sixteen-Definition ceiling and
the on-demand growth above the prewarmed count are unchanged. Twelve extra
pthreads are created when the orchestration SO loads, before any `host_orch` run,
and parked for its lifetime. After the change no gap on the submitting thread
contains a lane start, and its wait for recording to drain shrank from 1474 us to
41-368 us. The pool-growth unit test asked for five concurrent Graphs, which eight
prewarmed workers satisfy without growing; it now asks for nine.
Measured on a2a3, `--rounds 5` with the device run skipped, first pass per rank
dropped, per-phase minimum over the 8 warm passes:
phase main this delta
host_orch 2.314 1.291 -44%
graph_upload 0.451 1.384 +207%
sm_h2d 0.741 0.109 -85%
control-plane total 3.594 2.998 -17%
The reduction is real but much smaller than `host_orch` alone suggests, and the
shape of it is the point. Recording work leaves the submitting thread, so
`host_orch` drops; but seven Definitions are seven images to ship, so
`graph_upload` triples and takes back most of the win. `sm_h2d` falls because 129
task descriptors are shipped instead of 1131.
At the median the control plane does not improve: 3.883 ms against main's
3.715 ms. Main's single-recorder form is nearly deterministic (`host_orch` spread
2.314-2.469, 6%); this form spans 1.291-3.010 (133%) because its wall now depends
on seven recording threads getting CPU on a shared box. So this trades a
predictable cost for a lower floor and a higher ceiling, and on a loaded machine
the ceiling is what a caller sees.
`docs/investigations/2026-08-hbg-graph-block-decomposition.md` dropped this
decomposition as a regression, because between hw-native-sys#1897 and hw-native-sys#1929 `graph_begin` held
one recording slot and silently demoted a Graph whose key differed from the
in-flight recording's. hw-native-sys#1929's keyed in-flight map is the condition that entry
named for reconsidering it, so the entry carries the verdict and the measurement
above, and `graph_upload` is named as the stage that now dominates. The case's
README and docstring drop the 744-node/1131-task description of the single
Definition.
lwDavid
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The DeepSeek-V4 FLASH 43-layer decode scene test passes under tensormap_and_ringbuffer and fails on device under host_build_graph (`sched_error_code=100 SCHEDULER_TIMEOUT`, behind an AIV MTE bus fault). Three defects, one in the Graph recorder and two in the case, plus a fourth the block split of hw-native-sys#1936 hid rather than fixed. Recorder: - `graph_record_submit_node` derived a node's fanin from tensor args classified INTERNAL plus explicit `set_dependencies`. INTERNAL names whichever node's packed window holds the bytes — the ALLOCATOR, never the last writer — and the recorder consulted no tensor map, so the whole tensormap half of `compute_task_fanin` was missing inside a body. Every write-then-read through an `alloc_tensors` buffer or a boundary view was recorded unordered, and a Definition replayed a DAG the body does not have when its tasks are submitted individually. Measured on the pre-split single-Definition form of this body: 1348 edges against the 2143 the ordinary path computes for the same tasks, 543 of 561 comparable nodes short. On device that ran `csa_slots_build_valid_qk_plan` before the `topk` that fills its input, so `qk_pv_1` gathered KV pages at addresses the bus rejected. The recorder now runs the same `compute_task_fanin` and `register_task_outputs` the ring path runs, against a `PTO2TensorMap` owned by the recording — one per recording, since several record concurrently. Reusing those two functions rather than reimplementing the hazard walk is what makes the edge sets equal by construction. `begin_scope` / `end_scope` keep the body's own manual-scope depth so a manual scope suppresses inference here exactly as it does on the ring; they still never touch the real scope stack. Pool exhaustion or a failed allocation marks the recording unsupported, so the body falls back to the ordinary submit path rather than publishing a Definition with edges missing. Case (`decode_fwd_graph.cpp`): - `csa_moe_block` and `hca_moe_block` read the comm-window handles (`recv_*_ctx`, `*_arrived_ctx`, `routed_y_buf_ctx`) back as `int32_t` while the entry passes them as `uint64_t`, so the MoE all-to-all pushed to a truncated window address — an AIV MTE bus fault, not a wrong number. The peeled `hash_moe_l*_block` bodies already bound them correctly; the two loop bodies now match. - `csa_moe_block` chose its routing kernel with a host-side `if` on a per-layer boundary scalar. A body is recorded once per Definition key, so every replay would have used layer 2's `route_hash_1` where layers 4..40 need `route_sort`. The predicate travels as a Graph config value now, which `rt_submit_graph` folds into the key: eight Definitions for the pass, still within the eight the recorder pool prewarms. Runtime, separately: - `bind_graph_topology` bounded the Graph BOUNDARY scalar count by `MAX_SCALAR_ARGS`, which is `CORE_MAX_SCALAR_ARGS` (16, what one AICore task may take). A boundary is not a node payload: the recorder builds it with `Arg<GRAPH_MAX_TENSOR_ARGS, GRAPH_MAX_SCALAR_ARGS>` and the image hands it over as a pointer into the submission. The single-Definition form of this case passed 19 scalars and was refused on the device's first prepare pass as `sched_error_code=5 INVALID_ARGS`; cutting the pass into blocks brought every boundary under 16 and hid it. Bounded by `GRAPH_MAX_SCALAR_ARGS` now, so a wider boundary is legal again. The per-node cap is checked separately and is unchanged. Verified on two a2a3 dies: the tensormap_and_ringbuffer and host_build_graph cases both PASS, and the a2a3 host_build_graph ST suite is green.
lwDavid
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to lwDavid/simpler
that referenced
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Aug 21, 2026
The DeepSeek-V4 FLASH 43-layer decode scene test passes under tensormap_and_ringbuffer and fails on device under host_build_graph (`sched_error_code=100 SCHEDULER_TIMEOUT`, behind an AIV MTE bus fault). Three defects, one in the Graph recorder and two in the case, plus a fourth the block split of hw-native-sys#1936 hid rather than fixed. Recorder: - `graph_record_submit_node` derived a node's fanin from tensor args classified INTERNAL plus explicit `set_dependencies`. INTERNAL names whichever node's packed window holds the bytes — the ALLOCATOR, never the last writer — and the recorder consulted no tensor map, so the whole tensormap half of `compute_task_fanin` was missing inside a body. Every write-then-read through an `alloc_tensors` buffer or a boundary view was recorded unordered, and a Definition replayed a DAG the body does not have when its tasks are submitted individually. Measured on the pre-split single-Definition form of this body: 1348 edges against the 2143 the ordinary path computes for the same tasks, 543 of 561 comparable nodes short. On device that ran `csa_slots_build_valid_qk_plan` before the `topk` that fills its input, so `qk_pv_1` gathered KV pages at addresses the bus rejected. The recorder now runs the same `compute_task_fanin` and `register_task_outputs` the ring path runs, against a `PTO2TensorMap` owned by the recording — one per recording, since several record concurrently. Reusing those two functions rather than reimplementing the hazard walk is what makes the edge sets equal by construction. `begin_scope` / `end_scope` keep the body's own manual-scope depth so a manual scope suppresses inference here exactly as it does on the ring; they still never touch the real scope stack. Since the depth is now meaningful, the recording also refuses an auto scope opened inside a manual one, which the ordinary path reports as PTO2_ERROR_INVALID_ARGS — otherwise a Graph could record and replay a body ordinary submission rejects outright. Case (`decode_fwd_graph.cpp`): - `csa_moe_block` and `hca_moe_block` read the comm-window handles (`recv_*_ctx`, `*_arrived_ctx`, `routed_y_buf_ctx`) back as `int32_t` while the entry passes them as `uint64_t`, so the MoE all-to-all pushed to a truncated window address — an AIV MTE bus fault, not a wrong number. The peeled `hash_moe_l*_block` bodies already bound them correctly; the two loop bodies now match. - `csa_moe_block` chose its routing kernel with a host-side `if` on a per-layer boundary scalar. A body is recorded once per Definition key, so every replay would have used layer 2's `route_hash_1` where layers 4..40 need `route_sort`. The predicate travels as a Graph config value now, which `rt_submit_graph` folds into the key: eight Definitions for the pass, still within the eight the recorder pool prewarms. Runtime, separately: - `bind_graph_topology` bounded the Graph BOUNDARY scalar count by `MAX_SCALAR_ARGS`, which is `CORE_MAX_SCALAR_ARGS` (16, what one AICore task may take). A boundary is not a node payload: the recorder builds it with `Arg<GRAPH_MAX_TENSOR_ARGS, GRAPH_MAX_SCALAR_ARGS>` and the image hands it over as a pointer into the submission. The single-Definition form of this case passed 19 scalars and was refused on the device's first prepare pass as `sched_error_code=5 INVALID_ARGS`; cutting the pass into blocks brought every boundary under 16 and hid it. Bounded by `GRAPH_MAX_SCALAR_ARGS` now, so a wider boundary is legal again. The per-node cap is checked separately and is unchanged. Verified on two a2a3 dies: the tensormap_and_ringbuffer and host_build_graph cases both PASS, and the a2a3 host_build_graph ST suite is green. The scope rejection has a unit test that fails without the guard.
2 tasks
ChaoZheng109
pushed a commit
that referenced
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Aug 21, 2026
) The DeepSeek-V4 FLASH 43-layer decode scene test passes under tensormap_and_ringbuffer and fails on device under host_build_graph (`sched_error_code=100 SCHEDULER_TIMEOUT`, behind an AIV MTE bus fault). Three defects, one in the Graph recorder and two in the case, plus a fourth the block split of #1936 hid rather than fixed. Recorder: - `graph_record_submit_node` derived a node's fanin from tensor args classified INTERNAL plus explicit `set_dependencies`. INTERNAL names whichever node's packed window holds the bytes — the ALLOCATOR, never the last writer — and the recorder consulted no tensor map, so the whole tensormap half of `compute_task_fanin` was missing inside a body. Every write-then-read through an `alloc_tensors` buffer or a boundary view was recorded unordered, and a Definition replayed a DAG the body does not have when its tasks are submitted individually. Measured on the pre-split single-Definition form of this body: 1348 edges against the 2143 the ordinary path computes for the same tasks, 543 of 561 comparable nodes short. On device that ran `csa_slots_build_valid_qk_plan` before the `topk` that fills its input, so `qk_pv_1` gathered KV pages at addresses the bus rejected. The recorder now runs the same `compute_task_fanin` and `register_task_outputs` the ring path runs, against a `PTO2TensorMap` owned by the recording — one per recording, since several record concurrently. Reusing those two functions rather than reimplementing the hazard walk is what makes the edge sets equal by construction. `begin_scope` / `end_scope` keep the body's own manual-scope depth so a manual scope suppresses inference here exactly as it does on the ring; they still never touch the real scope stack. Since the depth is now meaningful, the recording also refuses an auto scope opened inside a manual one, which the ordinary path reports as PTO2_ERROR_INVALID_ARGS — otherwise a Graph could record and replay a body ordinary submission rejects outright. Case (`decode_fwd_graph.cpp`): - `csa_moe_block` and `hca_moe_block` read the comm-window handles (`recv_*_ctx`, `*_arrived_ctx`, `routed_y_buf_ctx`) back as `int32_t` while the entry passes them as `uint64_t`, so the MoE all-to-all pushed to a truncated window address — an AIV MTE bus fault, not a wrong number. The peeled `hash_moe_l*_block` bodies already bound them correctly; the two loop bodies now match. - `csa_moe_block` chose its routing kernel with a host-side `if` on a per-layer boundary scalar. A body is recorded once per Definition key, so every replay would have used layer 2's `route_hash_1` where layers 4..40 need `route_sort`. The predicate travels as a Graph config value now, which `rt_submit_graph` folds into the key: eight Definitions for the pass, still within the eight the recorder pool prewarms. Runtime, separately: - `bind_graph_topology` bounded the Graph BOUNDARY scalar count by `MAX_SCALAR_ARGS`, which is `CORE_MAX_SCALAR_ARGS` (16, what one AICore task may take). A boundary is not a node payload: the recorder builds it with `Arg<GRAPH_MAX_TENSOR_ARGS, GRAPH_MAX_SCALAR_ARGS>` and the image hands it over as a pointer into the submission. The single-Definition form of this case passed 19 scalars and was refused on the device's first prepare pass as `sched_error_code=5 INVALID_ARGS`; cutting the pass into blocks brought every boundary under 16 and hid it. Bounded by `GRAPH_MAX_SCALAR_ARGS` now, so a wider boundary is legal again. The per-node cap is checked separately and is unchanged. Verified on two a2a3 dies: the tensormap_and_ringbuffer and host_build_graph cases both PASS, and the a2a3 host_build_graph ST suite is green. The scope rejection has a unit test that fails without the guard.
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Summary
deepseek_v4_flash_decodesubmitted 1131 tasks from the submitting thread, so recording had almost nothing to overlap with: every kernel the submitter enqueued itself was a kernel no recording thread could be building at the same time. Cutting the whole forward pass into Graph blocks leaves the submitter 129 submissions and moves the rest onto the recording threads. Three changes:Seven Definitions cover all 43 layers (
examples/a2a3/host_build_graph/deepseek_v4_flash_decode/kernels/orchestration/decode_fwd_graph.cpp):csa_attn_block(50 nodes) /csa_moe_block(32) andhca_attn_block(35) /hca_moe_block(31) — the decoder loop's two alternating layer shapes, layers 2..41, plus layer 42 replayingcsa_attn_blockandhca_moe_block.swa_attn_block(28) — the two peeled sliding-window attentions of layers 0 and 1; their nodes are pairwise alpha-equivalent, so layer 1 replays what layer 0 recorded.hash_moe_l0_block(31) /hash_moe_l1_block(31) — the peeled MoE scopes. These cannot share a Definition:dispatch_waitfolds the MoE epoch in as a constant (32 at layer 0, 64 at layer 1) where the loop's variants take it as a scalar.The kernels, their order and their dependencies are unchanged; only where the host builds them moves.
graph_prepareasserts the boundary match instead of re-deriving it. It receives the handle of the recordinggraph_begincreated from the very boundary being prepared, so that recording cannot carry a different boundary — yetgraph_recording_boundary_matchescompared up to 128 ChipTensor descriptors a second time, 32-46 µs per recording, on the recording thread before its first node. It becomes adebug_assert; prepare drops to 13-35 µs. The search-based caller at the cache-lookup site keeps its real check, where the boundary is what identifies the recording.Eight recording workers are prewarmed instead of four. Growth happens inside
start()on the submitting thread, so seven Definitions paidpthread_createmid-burst: 170 µs and 98 µs gaps between Graph submissions, identified as three and one thread creations by annotating each gap with the recording lanes whose first record falls inside it. The 16-Definition ceiling and the on-demand growth above the prewarmed count are unchanged. After the change no gap on the submitting thread contains a lane start, and its wait for recording to drain shrank 1474 µs → 41-368 µs. Twelve extra pthreads are created when the orchestration SO loads and parked for its lifetime.Measurement
a2a3,
--rounds 5with the device run skipped, first pass per rank dropped, per-phase minimum over the 8 warm passes:host_orchgraph_uploadsm_h2dThe shape matters more than the
host_orchline: seven Definitions are seven images to ship, sograph_uploadtriples and takes back most of the win, andsm_h2dfalls only because 129 task descriptors are shipped instead of 1131.At the median the control plane does not improve — 3.883 ms against main's 3.715 ms. Main's single-recorder form is nearly deterministic (
host_orchspread 2.314-2.469, 6%); this form spans 1.291-3.010 (133%) because its wall now depends on seven recording threads getting CPU on a shared box. This trades a predictable cost for a lower floor and a higher ceiling; on a loaded machine the ceiling is what a caller sees.Docs
docs/investigations/2026-08-hbg-graph-block-decomposition.mdhad dropped this decomposition, because between #1897 and #1929graph_beginheld one recording slot and silently demoted a Graph whose key differed from the in-flight recording's (79 of 82 intended submissions recorded; host tasks rose 1131 → 1486). #1929's keyed in-flight map is exactly the condition that entry named for reconsidering, so the entry now carries the new verdict and the measurement above, namesgraph_uploadas the stage that dominates next, and the index line indocs/investigations/README.mdmoves with it. The case's README and docstring drop the 744-node / 1131-task description of the single Definition.Not updated: the reference table in
docs/dfx/hbg-bind-measurement.mdis pinned to777d4171and says so — its dsv4 host-task count (1131) becomes a pre-this-PR number, and re-pinning it needs a fresh measurement of every column, not just this one.Testing
clang-formatclean on every touched C++ fileHbgGraphAsyncSubmit.PrewarmedRecorderPoolGrowsPastThePrewarmedCountasks for nine concurrent Graphs (five no longer grows an eight-worker pool)deepseek_v4_flash_decodeismanual(368-kernel compile) and its unskipped device run is still blocked in Graph activation (sched_error_code=5 INVALID_ARGS), unchanged by this PR — the numbers above come fromSIMPLER_SKIP_DEVICE_RUN=1host runs on both ranks, which is what the case establishes today