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Support: split a bind phase's wall time into running and waiting - #2040
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📝 WalkthroughWalkthroughThe change records bind-thread and graph-recorder CPU counters in phase markers. It adds ChangesBind phase timing
Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: 🟡 Moderate · up to The diagnostic change can race with recorder shutdown and can report misleading phase metrics for overlapping spans. Because this may cause unsafe teardown behavior or incorrect performance data when enabled, the PR is not merge-ready until the issues are addressed. Poem
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Inline comments:
In `@docs/dfx/hbg-bind-phases.md`:
- Line 185: Update the cpu_ns table description to identify dur_ns - cpu_ns as
off-CPU time, noting that it includes both blocking and scheduler preemption
rather than only blocked time.
- Around line 187-188: Update the documentation for minflt/tminflt and
nvcsw/nivcsw in bind_kernel_counters to describe minflt and both context-switch
counters as process-wide deltas from RUSAGE_SELF; clarify that only tminflt is
thread-specific, and remove claims that these values represent bind-thread
blocking or preemption.
In `@simpler_setup/tools/README.md`:
- Around line 434-437: Correct the threshold explanation in the surrounding CPU
metrics documentation: describe reccpu/dur as recorder CPU time divided by wall
duration, approximately 1 for one recorder active throughout, below 1 for
partial overlap, and above 1 only when aggregate recorder CPU exceeds one
wall-time interval. Keep the existing cpu and dur definitions unchanged.
In `@src/a2a3/runtime/host_build_graph/host/graph_recorder_pool.h`:
- Around line 208-216: The shutdown join loop in both graph_recorder_pool.h
implementations must synchronize access to workers_ with worker_cpu_ns(). Update
shutdown() so the workers_ join operations are protected by mutex_ (or otherwise
prevent sampling from overlapping teardown), covering
src/a2a3/runtime/host_build_graph/host/graph_recorder_pool.h:208-216 and
src/a5/runtime/host_build_graph/host/graph_recorder_pool.h:208-216.
In `@src/a5/runtime/host_build_graph/host/runtime_maker.cpp`:
- Around line 227-233: Track nested counter-mark overwrites and emit an explicit
invalid state for every affected span in
src/a5/runtime/host_build_graph/host/runtime_maker.cpp#L227-L233 and
src/a2a3/runtime/host_build_graph/host/runtime_maker.cpp#L227-L233. Update
simpler_setup/tools/phase_time_split.py#L77-L82 to exclude invalid rows from
CPU-derived medians or suppress those metrics. Add a regression case where an
outer span’s mark is overwritten and its CPU time is below wall time.
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📒 Files selected for processing (8)
docs/dfx/hbg-bind-phases.mdsimpler_setup/tools/README.mdsimpler_setup/tools/phase_time_split.pysrc/a2a3/runtime/host_build_graph/host/graph_recorder_pool.hsrc/a2a3/runtime/host_build_graph/host/runtime_maker.cppsrc/a5/runtime/host_build_graph/host/graph_recorder_pool.hsrc/a5/runtime/host_build_graph/host/runtime_maker.cpptests/ut/py/test_phase_time_split.py
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Iteration 2 — all three macOS jobs ( Darwin does not provide it. This was not visible in iteration 1 because There was a second macOS error queued behind it that the aborted build never reached:
The guards cannot be compiled on this box (Linux), so they were checked by preprocessing the affected files with |
A phase's breakdown could say how long it took and how many faults it took, but not whether that time was spent computing or blocked — and the two send you to different places. `host_orch` is the case that matters: its faults are mostly on the Graph recorder threads, which run alongside the bind thread, so a fault count without this split reads as a cost the phase pays when it is a cost that overlaps. That reading is why the same tail was chased three times. - Each marker now carries `cpu_ns`, the bind thread's own CPU time, so a phase's `dur_ns - cpu_ns` is what that thread spent off CPU; `rec_cpu_ns`, every recording worker's summed, whose ratio to `dur_ns` is how many threads' worth of work ran alongside; and `tminflt`, the bind thread's share of `minflt`, so the recorders' share is the difference. - Times come from per-thread CPU clocks and never from rusage. `ru_utime` and `ru_stime` are accounted per scheduler tick, 10 ms at CLK_TCK=100, so on a phase of a millisecond they quantise to either zero or a whole tick: the values look plausible one at a time and are noise in aggregate. A per-thread clock reads the scheduler's running total in nanoseconds, and resolved a busy and a sleeping thread to under 10 us over a 1.29 ms window. rusage keeps the three counters, which are event counts and do not quantise. - Each phase carries its own counter mark, in the frame that opened it, alongside the start instant it already carried. A single mark held in one place is not enough: `bind_callable_to_runtime_impl` runs concurrently with itself whenever a Worker uses two-bank prepare — the capability `supports_concurrent_native_prepare` names and `tests/st/a2a3/host_build_graph/concurrent_prepare_stress` exercises — so two binds would overwrite each other's mark, and the loser would report counts measured from the other's start against its own duration. That is the mechanism behind the one row dsv4 reports with more CPU than wall, and it needed no nesting to happen. - The recorders' clocks are reachable through the pool that now owns them, so `GraphAsyncRecordingState::worker_cpu_ns()` reads them under the pool's own mutex. `shutdown()` moves the handles out of `workers_` under that mutex and joins them after releasing it, so a sampler cannot reach a handle mid-join and a worker can still reacquire the mutex inside `cv_.wait` to observe `stopping_` and exit — joining while holding it would deadlock. A thread that has already exited answers EINVAL and contributes nothing. - Two of the instruments are Linux-only and read zero elsewhere: sampling another thread's CPU clock needs `pthread_getcpuclockid` and a per-thread fault count needs `getrusage(RUSAGE_THREAD)`, neither of which Darwin has. Both are now behind `#if defined(__linux__)`. A bind is profiled on the silicon it binds to, so this costs nothing where it matters, but a `reccpu` of 0 in a log from a macOS `*sim` build means "not measurable here" rather than "nothing ran alongside" — which both docs and the tool now say. - `simpler_setup.tools.phase_time_split` reports the split per phase, with cold and warm binds as separate rows rather than the cold one dropped: a cold bind pays the one-off cost of standing recorder storage and the arenas up, and its size is the thing worth knowing. The tool still flags a row whose CPU exceeds its own wall, but that is now a backstop rather than a known limitation: with the mark per phase, a non-zero count means the runtime has a defect, so the message says to report it. `nvcsw` and `nivcsw` come from `RUSAGE_SELF` and so count the whole process, recorders included; only `tminflt` is thread-scoped. Both docs said or implied they isolate the bind thread, which would have made every future reading of them wrong. `dur_ns - cpu_ns` is likewise off-CPU time — blocked *and* runnable-but-preempted — not blocked alone, and `rec/dur` sits below 1 for a single partially-overlapping recorder rather than above 1 for any overlap at all. No behavior changes outside the SIMPLER_HBG_BIND_BREAKDOWN_ENABLE diagnostic: both sampling sites are already behind it, so a default run reads no clock and takes no pool lock. The `shutdown()` ordering change is unconditional but does not alter what teardown does. Testing: full product build across both arches, cpput 122/122 from a clean build directory, `pytest tests/ut/py` 2014 passed / 18 skipped, both sim sweeps green with zero failures, and `tests/ut/py/test_phase_time_split.py` 10/10. The two `#if defined(__linux__)` guards cannot be compiled here — this box is Linux — so they were checked by preprocessing the affected files with `-U__linux__` and confirming the guarded calls are gone, with only glibc's own declaration of `pthread_getcpuclockid` surviving. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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Summary
A phase's breakdown could say how long it took and how many faults it took, but not whether that time was spent computing or blocked — and the two send you to different places.
host_orchis the case that matters: its faults are mostly on the Graph recorder threads, which run alongside the bind thread, so a fault count without this split reads as a cost the phase pays when it is a cost that overlaps. That reading is why the same tail was chased three times (see the entry amended by #2036).cpu_ns, the bind thread's own CPU time, so a phase'sdur_ns - cpu_nsis what that thread spent off CPU;rec_cpu_ns, every recording worker's summed, whose ratio todur_nsis how many threads' worth of work ran alongside; andtminflt, the bind thread's share ofminflt, so the recorders' share is the difference.ru_utime/ru_stimeare accounted per scheduler tick — 10 ms atCLK_TCK=100— so on a phase of a millisecond they quantise to either zero or a whole tick: the values look plausible one at a time and are noise in aggregate. A per-thread clock reads the scheduler's running total in nanoseconds; measured against a busy and a sleeping thread over a 1.29 ms window it resolved both to under 10 µs. rusage keeps the three counters, which are event counts and do not quantise.GraphAsyncRecordingState::worker_cpu_ns()reads them under the pool's own mutex — a worker being created or joined concurrently cannot be sampled through a dangling handle, and one that has already exited contributes nothing.simpler_setup.tools.phase_time_splitreports the split per phase, with cold and warm binds as separate rows rather than the cold one dropped: a cold bind pays the one-off cost of standing recorder storage and the arenas up, and its size is the thing worth knowing.What it reads on dsv4
Two things a duration alone could not say:
host_orch's 961 cold faults are almost all not the bind thread's (tminflt64) and sit inside 2.3 threads' worth of overlapping work, andgraph_upload's cold bind is 45% waiting rather than computing.One limitation, flagged rather than hidden
The counter mark is a single global (introduced with
bind_phase_begin()in #2022) and the segments do not nest, so a segment that opens while another is still open takes that one's mark with it. The symptom is a row reporting more CPU than the segment's own wall, which on dsv4 isargs. Such a row'scpu/offcpudescribe neither segment, so the tool marks it!and explains why. Clamping off-CPU to zero and printing it would read as "ran the whole time" — the opposite of what an unusable mark means.Testing
No behavior changes outside the
SIMPLER_HBG_BIND_BREAKDOWN_ENABLEdiagnostic: both sampling sites are already behind it, so a default run reads no clock and takes no pool lock.pytest examples tests/st --platform a2a3sim --device 0-15 --manual include— one pre-existing failure,TestSpmdPagedAttentionHighPerf::b4_h32_kv8_s512_bs128_fp16golden mismatchpytest examples tests/st --platform a5sim --device 0-15 --manual include— greenctest --test-dir tests/ut/cpp/build -LE requires_hardware— 119/119pytest tests/ut -m "not requires_hardware"— 1951 passed; one failure intest_second_child_failure_reaps_first, a wall-clock budget on a forked child that passes alone and is load-dependent-m "not sdma" --exclude-level 4 --manual include— 1 failure,TestPagedAttentionHostBuildGraph::Case1'sprepare_native_run failed with code -1000, reproduced on the base commit