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Place a peer host's work by the frame that dispatched to it - #2217
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📝 WalkthroughWalkthroughThe change adds frame identity tracing for remote dispatches, emits spans on serving peers, pairs those spans across host clocks, and places remote host activity in the caller’s dispatch window. Tests and documentation cover tracing, containment, placement, and validation. ChangesRemote task tracing
Priority: ➖ Normal Estimated code review effort: 4 (Complex) | ~60 minutes Change: Feature Sequence Diagram(s)sequenceDiagram
participant WorkerThread
participant RemoteL3Endpoint
participant remote_l3_session
participant swimlane_converter
WorkerThread->>RemoteL3Endpoint: submit remote TASK frame
RemoteL3Endpoint-->>WorkerThread: return frame header attributes
remote_l3_session->>remote_l3_session: emit remote_task span on peer
swimlane_converter->>swimlane_converter: pair caller and peer spans
swimlane_converter->>swimlane_converter: place peer spans in caller dispatch window
Merge Risk: 🟡 Moderate · up to Some merged traces can either fail conversion or show incorrect remote-task placement. These issues should be corrected before merge. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
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In `@simpler_setup/tools/containment.py`:
- Line 1038: In the dispatch construction flow, validate that each frame key is
not already present in dispatches before assigning (frame, handoff). Reject
duplicate caller frame keys for all inputs, including those with a single peer
window, so _close_dispatch() cannot match an overwritten caller.
In `@simpler_setup/tools/swimlane_converter.py`:
- Line 3787: Update the host_spans filtering in remote_chain() to retain only
axis-process PIDs, excluding peer and unplaceable beside_a_peer processes before
local span selection; continue routing peer processes through peer_spans.
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📒 Files selected for processing (14)
docs/dfx/host-trace.mdpython/simpler/remote_l3_session.pysimpler_setup/tools/README.mdsimpler_setup/tools/containment.pysimpler_setup/tools/strace_timing.pysimpler_setup/tools/swimlane_converter.pysrc/common/hierarchical/remote_endpoint.cppsrc/common/hierarchical/remote_endpoint.hsrc/common/hierarchical/worker_manager.cppsrc/common/hierarchical/worker_manager.htests/ut/cpp/hierarchical/test_remote_endpoint.cpptests/ut/py/test_containment.pytests/ut/py/test_remote_l3_protocol.pytests/ut/py/test_swimlane_converter.py
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All four addressed in 337e50f.
Rate (containment.py:778). The arithmetic is as you set it out — at 100 ppm a true 10 us slack measures 6 us, and the claim in the description that the rate was "already inside the measured slack" was wrong. slack_ns now carries it: the derivation is S - M = T_p(e_p - e_c) - S·e_c, bounded by T_c × MAX_RELATIVE_RATE, so only the difference between the two rates carries — two clocks off by the same amount leave an error proportional to the slack itself. rate_bound_ns is published beside the total, since only the measured half shrinks when a window tightens. 1.3 us on the 13.3 ms window #2134 measured across two hosts.
same_axis (containment.py:794). You are right about the consequence and I want to be precise about which half. The position was within bound — if the peer's raw window sits inside the caller's, the true offset is at most the slack, so the recorded instant is within slack_ns of the truth either way. What was wrong was reporting 0 slack, which claims exactness. The window now stays in the chain: the peer keeps its recorded instant, the bound is published all the same, and because the truth can lie either side of an observed instant the lane reads observed, ±N us rather than placed, +N us. metadata gained drawn_at_ns and observed so the bound and the drawn position are two separate facts. Keeping the position matters on a loopback session, where placing would collapse the real dispatch-to-serve latency to zero.
Axis inference (containment.py:958). Dropped entirely rather than patched — your counterexample is the general case, and I found a second one while testing: two clocks reading close enough put local processes inside the peer's extent too, which made axis_pids come out empty and killed the merge with a misleading "no runner_run pair". No rule over the timestamps can separate the two machines. So the merge now vouches rather than infers: a process at the top of a chain, or one whose own device window the merge is of; everything else is left out. Peers are excluded from that set as well, or a peer that also has a device window would be drawn twice.
Half-open window (containment.py:899). < now, with an end-boundary regression test.
Verification: tests/ut/py 2318 passed, onboard TestL3Group on a2a3 passes, and a same-host merge is unchanged down to the bytes of traceEvents.
Two hosts that exchange a task share no clock, so the cross-Rank merge refused anything from a second machine: comparing the two axes would be wrong rather than loose. The refusal was wider than the problem. What two axes cannot answer is where an instant on one sits on the other, and placing a peer needs no such answer - a remote dispatch blocks from publishing its frame until the completion arrives, so everything the peer did happened inside that window, and the spare width between the two durations is the bound. Each duration is timed where it happened, so the peer's boot time cancels out of the result. What the subtraction does assume is that the two machines agree on how long a second is, and that assumption is not free: a relative rate difference between the two counters biases the bound and is not inside it. The rate is left out rather than modelled, because it is unknown here - the one attempt to read it came out -813, +195, +2105 and -631 ppm across four launches with the signs disagreeing, endpoint noise over a ~10 ms baseline rather than a rate - and a bound built on a datasheet figure nobody checked is the estimate containment exists to replace. So `slack_ns` is what the logs measured: a gap under it is undecided, and a gap just over it is decided only to within a rate nobody has bounded. What was missing was a name both sides write down. The wire already carries one: every `remote_l3` frame header holds `(session_id, worker_id, sequence)`, the sender allocates the sequence per endpoint, and the peer decodes all three immediately before it serves the frame. So the join needs no protocol field and no version bump. - `WorkerEndpoint::progress_frame_attrs()` reports the header of the last frame an endpoint published, and the scheduler appends it to `<level>.dispatch`. An endpoint that publishes no frame, which is every local mailbox, reports nothing. The header is kept as its fields rather than as text, because `submit_progress` is on the dispatch path and a run may never read the trace. - The peer brackets its service of one frame in `<level>.remote_task`, carrying the same header as one `frame=<session>:<worker>:<sequence>` token. One field rather than three: a dispatch's attributes already run most of the way to the record's 192-byte capacity, and three `frame_*=` names overran it, which cut the last one short and left a key that read as present but was half written. Joined, the three arrive together or not at all, and a record the capacity did cut short says so rather than pairing nothing in silence. - That span closes before the completion frame goes out. The caller is released by that frame and can have handled its completion before the peer's write returns, so a span that closed after it would report work the caller's own window had already ended - the one thing the window has to be able to say it contains. - `containment.remote_windows` pairs the two sides on that header and reports the caller window, the peer window, and the slack between them. A peer window wider than its caller's describes no containment and is dropped, since the usual cause is two logs from different runs whose sequence numbers collide. One frame served by two windows refuses outright: that is the whole pile being wrong rather than one pair. - The merged trace draws the peer's processes in the dispatcher block, each lane labelled with its bound and every slice repeating it as `slack_ns`, with `metadata.remote_windows` carrying the record per frame. The spans that opened and closed a frame window are drawn too, so the trace shows what placed the block and not only the block. Offsets inside one frame keep their exact values, being one clock's. - A peer that dispatched on to a further peer is reached in as many hops as the pile holds: each window puts an instant on the clock of the process that dispatched, and the next takes it from there. The slacks add, because the freedom one window grants is freedom the windows above it cannot take back. Windows naming each other's process reach no axis at all and refuse rather than loop. A Rank whose own window a peer recorded is rebased the same way, so every reader of the resulting placement is correct without having to know a second hop happened. - Ranks still have to share one Host clock. A frame window places the process it was served by, never the chip children under it - those are other pids in other logs that no window names - so nothing puts a second machine's Rank on this axis. - A peer whose own timestamps already fall in the window keeps them. That happens when the two logs share a clock and also when two machines booted within the window's spare width of each other; neither reading has to be settled, since under both the recorded instant is within `slack_ns` of the truth. The position stays observed rather than derived, which keeps the real gap between the dispatch and the peer picking the frame up where placing would collapse it to zero, and the lane says `observed, +-N us` rather than `placed, +N us` because the truth can lie either side of it. - A process the pile cannot vouch for is left out. Two machines' clocks can read however close to one another, so no rule over the timestamps separates a local process from one of the peer's; what the merge vouches for is a process at the top of a chain, one whose own device window the merge is of, and one that dispatched such a window. The third is what reaches the levels between the other two: a scheduler below the root and above a chip owns no window and heads nothing, and without it a spliced trace drops a lane that a same-host merge draws. It is reached by the dispatch identity a scheduler and its chip's `chip.run` both write, which is the join the capture pairing already runs on; those fields count per run, so the dispatcher among two machines writing the same four numbers is the one whose own log covers the instant the window opened. That compares no clock across a boundary - a process whose whole recorded life excludes an instant cannot have dispatched what began there. Collecting the peer's log directory brings its other processes along, and those are dropped rather than drawn where nothing places them. One pid writing two Host logs makes every pid ambiguous - a span names its process by pid alone - and refuses the merge outright. - A frame window is half-open, so the instant it ends at belongs to whatever the peer did next rather than to a frame that has closed. - A frame named by two dispatch spans refuses, as one served by two peer windows already did. Keeping the later would replace the earlier dispatch's window with a different, later interval and close the wrong end of it. - An endpoint drops its published header before anything in a submission can throw. A failed submission that reported the previous frame's header would name it twice, and the later span's window would silently replace the real one. The scheduler reads the header while the dispatch still holds admission, for the same reason in the other direction. Both paths that a run pays for are kept off the work they measure. The peer serves a gated-off frame through one reused do-nothing context manager rather than building a generator per frame, 1.9 us down to 0.45 us. A chain finds an instant's window by bisecting that peer's windows rather than scanning every frame the run dispatched, which takes placing a 500-frame log from 4.0 s to 0.12 s and leaves the per-span cost flat at 2.3 us where it had been growing with the frame count. - A host-family process is labelled by its own level word rather than by the family, because a spliced trace holds several at once and `node`, `network1` and the levels above it are different schedulers with the same lane shape. `endpoint_kind_name` gains its MPI group case, which fell through to `unknown` and so hid the transport on exactly the dispatches this key exists to follow. An L4 example can now ask for the capture this merge reads. Each of them built a bare `CallConfig()`, so no run of one turned a capture on and the merge had no input any machine could produce - only spans written by hand in tests. `global_tload_mixed_l3` forwards `--enable-chip-swimlane` and `--output-prefix` into the config every dispatch carries, which the remote L3 decodes off the wire, so one flag reaches both machines. Two ranks on two hosts still land on `rank0/d0` apiece and have to be collected apart, that being a property of the storage convention rather than of this flag. Tests reach the frame grammar through `format_frame_key`, which sits beside the parser that reads it, and build their records through one constructor rather than spelling the prefix out at each of the fourteen places that needed a log. A test that repeats a format can go on passing while describing one the code no longer writes - which is how the endpoint's own test came to assert three fields against a token that holds one. A merge with no peer in it is unchanged, down to the bytes of `traceEvents`.
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Why
Two hosts that exchange a task share no clock, so the cross-Rank merge refused
anything from a second machine: comparing the two axes would be wrong rather
than loose. The refusal was wider than the problem. What two axes cannot answer
is where an instant on one sits on the other, and placing a peer needs no such
answer — a remote dispatch blocks from publishing its frame until the completion
arrives, so everything the peer did happened inside that window, and the spare
width between the two durations is the bound. Each duration is timed where it
happened, so the peer's boot time cancels out of the result.
What was missing was a name both sides write down. The wire already carries one:
every
remote_l3frame header holds(session_id, worker_id, sequence), thesender allocates the sequence per endpoint, and the peer decodes all three
immediately before it serves the frame. The join therefore needs no protocol
field and no version bump.
What this does
WorkerEndpoint::progress_frame_attrs()reports the header of the lastframe an endpoint published, and the scheduler appends it to
<level>.dispatch. An endpoint that publishes no frame — every local mailbox— reports nothing. The header is kept as its fields rather than as text,
because
submit_progressis on the dispatch path and a run may never read thetrace. It is dropped before anything in a submission can throw: a failed
submission reporting the previous frame's header would name it twice, and the
later span's window would silently replace the real one.
<level>.remote_task,carrying the same three.
containment.remote_windowspairs the two sides on that header andreports the caller window, the peer window, and the slack between them. A peer
window wider than its caller's describes no containment and is dropped — the
usual cause is two logs from different runs whose sequence numbers collide.
One frame served by two windows refuses outright: that is the whole pile being
wrong rather than one pair.
as many hops as the pile holds, and the slacks add, because the freedom one
window grants is freedom the windows above it cannot take back. Windows naming
each other's process reach no axis at all and refuse rather than loop.
sitting inside the caller's means either one machine or two that booted within
that window's own spare width, and under both readings the recorded position
is right to within the bound placing it would publish. Placing it would move
it to the window's start and so collapse the real gap between the dispatch and
the peer picking the frame up — which is what a loopback run exists to show.
process by pid alone and two machines number theirs independently. A process
is taken off the axis on positive evidence — its interval overlapping a
peer's — never on the absence of it, since a local process that ran before the
dispatch shares no instant with it either. One pid writing two Host logs makes
every pid ambiguous and refuses the merge.
process it was served by, never the chip children under it, so nothing puts a
second machine's Rank on this axis.
trace holds
node,network1and the levels above it at once.endpoint_kind_namegains its MPI group case, which fell through tounknownand so hid the transport on exactly the dispatches this key exists to follow.
Cost
Both paths a run pays for are kept off the work they measure.
The remote dispatch span itself is 20.8 us P50 (
#2134), so the attribute costis ~1.5% of it and the local path is unchanged. The peer's own saving comes from
serving a gated-off frame through one reused do-nothing context manager rather
than building a generator per frame. A chain finds an instant's window by
bisecting that peer's windows rather than scanning every frame the run
dispatched, which leaves the per-span cost flat at 2.3 us where it had been
growing with the frame count.
Verification
tests/ut/py: 2318 passed, 0 failed. 30 new cases, including that moving onemachine's clock 900 days changes nothing the placement reports, that a
three-level chain sums its two slacks, that a failed submission publishes no
header, and that a peer whose timestamps already land in the window keeps
them while still reporting its bound.
ctest: the endpoint, scheduler and worker-manager suites pass, with a newcase reading the reported header back out of the frame that actually left the
process.
task-submit:TestL3Group(2 cards) and a single-cardhost_build_graphcase pass. The L3 dispatches carryendpoint_kind=local_mailboxand no frame header, which is what an endpointthat publishes no frame should report.
traceEvents,against a capture taken today on this branch.
Not covered
writes no
chip_swimlane_records.jsononmaintoday — bisected to0cc51adf(Hold host-orchestration phase state per pipeline slot #2204), reproduced on a clean748c39fbwith no local changes —so there is no current capture for the cross-Rank path to convert. What is
verified against fresh data is the single-card chip trace; the L3 comparisons
this branch was developed against used a capture from before that regression,
which shows the converter unchanged but not the path end to end.
tests over synthetic logs from three machines, and the single-host half of the
key is exercised onboard, but nothing here has been through two machines. The
environment that would do it is the one
#2134measured on, where a ~21.5 stimeout fires in batches.
the production code names a level: the pairing reads the leaf after any level
word and the peer builds its span name from its own level. Their remote
composition is still proposed rather than implemented
(
docs/hierarchical-level-runtime.md).Refs #2134