Fix: redirect host spans to per-process buffered files - #1945
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📝 WalkthroughWalkthroughChangesThe host logger now supports Host span file logging
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🟠 High · up to File-backed host tracing can currently deadlock in a child process after a multithreaded fork and can omit the required stderr clock anchor, making production tracing unreliable and potentially affecting process availability. These issues should be fixed before merge; the test and documentation follow-ups also need attention. Sequence Diagram(s)sequenceDiagram
participant HostLogger
participant HostSpanFileSink
participant LogFile
participant Stderr
HostLogger->>HostSpanFileSink: write host span when SIMPLER_HOST_STRACE_DIR is set
HostSpanFileSink->>LogFile: append [STRACE] record
HostSpanFileSink-->>HostLogger: return success or failure
HostLogger->>Stderr: use existing log path when file output fails
Poem
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
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Actionable comments posted: 5
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Inline comments:
In `@docs/dfx/host-trace.md`:
- Around line 30-31: Update the host trace documentation around the file-sink
fallback description to state that host spans fall back to stderr when path
setup, file opening, fprintf(), or depth-zero fflush() fails, while preserving
the existing notes about ordinary logs and the clock anchor.
In `@src/common/log/host_log.cpp`:
- Around line 374-378: In the successful file-sink branch of host span logging,
call emit_clock_anchor_if_needed() before returning so file-backed spans still
emit the clock anchor. Add coverage requiring exactly one [CLOCK_ANCHOR] record
and no [STRACE] record on stderr for this path.
- Around line 172-180: Update the fork lifecycle around sink.mutex and
sink.stream so the child process can safely call write_host_span_file() after a
multithreaded fork: reinitialize or otherwise release the inherited mutex, and
close the inherited stream descriptor without flushing copied stdio buffers
before clearing sink state. Do not leave the child blocked on the inherited lock
or leak descriptors across fork generations.
- Around line 374-376: Add a reproducible multi-process profiling workload
covering stderr-baseline and file-sink scenarios, and record measurements
quantifying tracing-overhead reduction for the SIMPLER_HOST_STRACE_DIR path in
write_host_span_file. If that validation cannot be included, remove or defer the
configuration-surface change around SIMPLER_HOST_STRACE_DIR to a separate
change.
In `@tests/ut/cpp/a5/test_host_log_off.cpp`:
- Around line 380-382: Update the assertions in the host-log test so the root
record is matched with an unambiguous field sequence that cannot be satisfied by
name=chip.run.bind; alternatively, parse the two newline-delimited records and
assert each record’s exact name. Preserve the existing checks for both records
and the expected two-line output.
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复现了 PR 描述里的问题背景，也在本地跑了完整验证：base 先说结论：问题是真的，fork 处理写得也对。 下面按严重程度列。有两条需要维护者拍板，两个测试有实质缺陷。 需要拍板（不是代码缺陷）新增了一个控制行为的环境变量。 你测到的开销问题是真的，而且晚于那个设计决定，所以这是「改设计」还是「换机制」的选择，不是我能替维护者定的。 如果要一个不引入 C++ 可见环境变量的做法：把目录通过已有的 Must-fix：
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更正我上面那条关于 我把它写成「新增行为门控需要维护者签字，另外这里有个替代方案」。实际结论应该更直接：这个环境变量不需要存在，而且理由不是流程，是本仓已有的契约。
三点：
具体改法： 这样一并消掉的东西：新增环境变量、每条 span 一次 抱歉绕了一圈 —— 你测到的问题和 fork 的写法我仍然认为是对的，只是这个值不该从环境里取。 |
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@high-cloud 我把上面两条 review 的修法直接推到这个分支上了（作者仍然是你，我只是 committer），并 rebase 到了当前 main（原 base 落后 11 个提交）。折成一个提交，diff 只动 8 个文件。如果你不同意任何一处，直接改掉或让我回退。 改了什么1. 去掉 2. STRACE 记录只格式化一次，两个 sink 共用同一份字节。 原来 file 路径手写了第二份记录语法，和 60 行外那份并存 —— 那正是 #1792 item 2 存在的原因（上一次两份只差一个 3. fork 测试补上了唯一能看见那个 bug 的断言。 我把子进程改成 4. 两个目录测试改用作用域守卫，并各自设自己的级别。 原来 一件我在推之前去查了业界做法的事拿了三份一手资料：Linux ftrace 文档、Perfetto buffers 文档、OpenTelemetry SDK 规范。四条共同不变量：
支持这个判断的是你自己的数字：validation max 16.836 → 7.291 ms，不是降到接近 0。如果 I/O 真被移出被测路径，残留不该还有 7 ms 量级；7.291 ms 与「flush 尾巴仍落在发射线程上」一致。 所以我没有重写它 —— 完整形状（per-thread 无锁缓冲 + 后台 flush + 丢弃计数）是 #1792 item 6 的范围。我只加了两处，让它不声称超出实际做到的： 两件我没做，留给你或后续
验证
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补上读取侧 —— 一个进程一个文件把原来的一条流拆开了，所以工具那边得跟着动。两处，都在 1. 多输入 + 目录展开，手工 merge 这一步消失。 以前是一个位置参数、一次 python -m simpler_setup.tools.strace_timing <output_prefix> run.stderr --swimlane swimlane.json你在验证里写的 "four per-PID host STRACE files merged after execution" —— 那个 merge 步骤现在不需要了。（目录里没有 span 文件时报错退出，而不是静默当成一个空 log。） 2. 一个 pid 有 span 却找不到 anchor 时警告。 这是这次拆分里唯一一处完全没有信号的损失。 对比一下：这个工具在别的场合是会说话的 —— 一个 pid 有多条 anchor 会警告"using the last one"，记录被撕裂会警告"N of M records are incomplete"。偏偏 anchor 数为 0 时一句都没有。 现在会说： 这个 PR 让文件成为「开了诊断就默认」的路径，所以撞上它的人会变多 —— 引入一个失败模式而不让它可见，是这条 track 上我一直在挑的同一种毛病，所以并在这里而不是留作后续。 doc 里补了收集配方，并写明漏掉 stderr 抓取的后果和那条警告是唯一信号。 下游继承：pypto-serving 的 验证
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@high-cloud 把这个 PR 的设计往回收了一步、变简单了。根因不是"漏了 anchor 和 bind phase"，是选 sink 的决定放错了层。 之前的形状为什么必然"一边一点"目的地既不是字段也不是参数，而是唯一那个写函数里的常量 —— 而那个函数叫 bool write_stderr(const char *record, size_t size) {
... ::write(STDERR_FILENO, record + offset, size - offset);所以谁需要换目的地，只能在 logger 之上决定。这个 PR 原来的做法是在 （这条根因是维护者指出来的，我前几轮一直在给那个放错的位置找理由，甚至发明了一套"机器记录 vs 人读记录"的分类 —— 那是错的方向：spans / anchor / bind phase 只是日志系统的使用者，不需要被区分。） 现在的形状sink 是 logger 的一个配置项，跟阈值同一个位置（共享状态，binder 已经把指针发给每个 DSO）： 于是所有经过它的记录自动跟随：
顺带解决的两件事anchor 现在和它的 span 在同一个文件里，所以每个文件对恢复 wall time 是自洽的 —— 不再需要"span 文件 + stderr 抓取"两个来源。读取侧那条警告的含义也随之变了：从"你漏了 stderr"变成"某个输入不完整"。 文件名 明确留在控制台的Python 通过自己 所以这个 PR 之后准确的状态是：所有经过 unified logger 的记录在 验证
阴性对照（证明新不变量是被钉住的）：把 之前那版还在的东西都留着： |
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Host log records were written synchronously to stderr, which in a profiled multi-rank run is one shared pipe. A consumer that does not drain it promptly blocks the emitting thread inside write(2): 0.01-0.07 ms validation copies were separated by 10.10-18.44 ms of unnamed gap, sitting exactly on marker flush boundaries, so the tracer was the dominant term in its own trace. The destination was not a field or a parameter but a constant inside the one writer, in a function called write_stderr. So a caller that needed a different destination could only decide above the logger, which is why the first shape of this change routed inside the span emitter and left the clock anchor and the bind-phase summaries behind: the sink had become a property of one call site rather than of the logger. - The logger takes an output directory and writes <dir>/host.<pid>.log. It comes from CallConfig.output_prefix, already the directory every diagnostic artifact goes under and whose contract is that the runtime never derives a path itself, so the presence of a prefix is the whole condition and there is no new switch. The first non-empty path in a process wins; the submit path and the forked chip child each seed their own logger from the config they already hold. - One place chooses a destination, and it chooses per logger. Every record follows: LOG_* records, [STRACE] spans, [CLOCK_ANCHOR], bind phase= summaries, and the spans Python emits through unified_log_host_span. No caller declares anything, no record kind is special, and there is no state in which part of a run's log is in one place and part in another. A process that cannot open its file falls back to stderr for that record rather than losing it. - Each file is fully buffered, flushed when a depth-zero invocation completes and on any WARN or ERROR. Direct four-rank run: runner-to-validate gap p95/max 0.150/0.538 ms -> 0.051/0.164 ms, validation max 16.836 -> 7.291 ms. - Format the STRACE record once and let the writer place it. The grammar had a second copy, which is the divergence hw-native-sys#1792 item 2 exists to prevent: its previous instance differed only in an inv conversion. - Make the sink fork-safe: lock across the fork boundary, reopen a child-owned file, and close the inherited descriptor without flushing the parent's copied stdio buffer. Because a process's anchor now lands in the same file as its records, each file is self-contained for wall-clock recovery. strace_timing.py takes several inputs and concatenates them - every record already carries its pid - and a directory expands to the host.*.log files inside it, so a run's output_prefix can be passed as-is. It also warns when a pid emitted spans and no anchor was found for it, which now means an input arrived incomplete rather than that a stream was left out. Messages Python logs through its own logging module stay on the console. That is a second logging system with the same threshold and a different envelope - no timestamp, no thread id - so its records cannot be ordered against this stream wherever they are written, and pointing it at the same file would put two envelopes and two buffered writers in one place. Making it a client of this logger is a separate change. What this deliberately is not: the flush runs on the thread that emitted the record, where ftrace and Perfetto hand bytes to a consumer and never let a producer touch the output, and a full buffer blocks that thread rather than dropping and counting, where every comparable tracer bounds its buffer and exports a loss counter. The gain is one write per flush boundary instead of one per record - an order of magnitude, not the removal of the observer effect, which is why a residual tail remains. A drop counter is hw-native-sys#1792 item 6's first stage and is still open. Tests cover one buffered file per process holding the anchor and the spans with nothing left on stderr — each record pinned by its whole field sequence, since a span name can be a prefix of a longer one — an ordinary record following the same way with severe ones flushed as written, parent/child file ownership, the submit path seeding the directory, and on the reader side a multi-input run, a directory expansion, and the missing-anchor warning. The fork case asserts the parent's file does not yet hold the parent's unflushed record, which is the only place a wrongly flushed inherited buffer is visible; asserting on the child's file alone passes even when the child flushes the parent's bytes. Both directory tests bind through a scope guard, so one cannot redirect a later test's records, and each sets the level it needs rather than inheriting one from an earlier test in the same binary. Related to hw-native-sys/pypto-serving#179.
Python and C++ were two logging systems that agreed only on a threshold. `Worker.init()` pushed the `simpler` logger's level into the native state, but a Python record was then formatted by whatever handler sat on the root logger as `[%(levelname)s] %(message)s` — no monotonic timestamp, no thread id. So a Python record could not be ordered against a C++ one no matter where either was written, and it went to the root logger's handler rather than to the host logger's own output. The issue this belongs to is titled *one clock, one grammar, one gate*; the Python side had the gate and neither of the others. Seeding the native threshold now also installs a handler on the `simpler` logger that forwards each record through `unified_log_*`, so every record in the process shares one envelope, one clock and one destination. - One new binding, `_emit_host_log(level, func, message)`, hands an already-formatted message to `HostLogger::log`. The message is passed as a `%s` argument, and a level outside the ladder is refused rather than cast. - A record's level is rounded toward the milder name (`35` becomes `WARN`), the opposite direction from `_normalize_threshold`: asking for a *threshold* of 35 must not silently admit warnings, but a record at 35 is a warning someone gave a custom number. - `propagate` is deliberately untouched, so a record still reaches the root logger as well. That keeps an interactive console readable and keeps `caplog.at_level(..., logger="simpler")` working — five test files assert on warnings that way. The host log is the complete copy; the console is a view of it. Turning propagation off would make the file the only destination and blind all of them. - The handler is installed where the threshold is seeded, not at import. `import simpler` has to keep working when `_task_interface` is missing or stale, which the build-stamp guard makes routine on every source-tree move until a rebuild, so putting the extension on the import path of the logging surface would lose the logger exactly when it is needed to explain why. Records logged before a worker is initialized stay on the root handler. - The handler swallows its own failures through `handleError`: a logging call must not become the reason a run fails. Tests cover the forwarded level/func/message, that propagation and `caplog` survive, idempotent installation, the rounding direction, that a failing sink does not raise into its caller, and that `import simpler` installs nothing. One of them exists specifically because the others do not need it: every other test installs the handler itself, so without a test that `_initialize_host_log` installs it, the production line doing so could be deleted with the suite staying green. Verified by removing that line — exactly one test fails. hw-native-sys#1945 gave the host logger a configurable destination, so a run's Python records now join its C++ records in `<output_prefix>/host.<pid>.log`. That PR's own description of what stays on the console is corrected here in the same change: it said routing Python's records through the host logger was a separate change, which this is.
Python and C++ were two logging systems that agreed only on a threshold. `Worker.init()` pushed the `simpler` logger's level into the native state, but a Python record was then formatted by whatever handler sat on the root logger as `[%(levelname)s] %(message)s` — no monotonic timestamp, no thread id. So a Python record could not be ordered against a C++ one no matter where either was written, and it went to the root logger's handler rather than to the host logger's own output. The issue this belongs to is titled *one clock, one grammar, one gate*; the Python side had the gate and neither of the others. Seeding the native threshold now also installs a handler on the `simpler` logger that forwards each record through `unified_log_*`, so every record in the process shares one envelope, one clock and one destination. - One new binding, `_emit_host_log(level, func, message)`, hands an already-formatted message to `HostLogger::log`. The message is passed as a `%s` argument, and a level outside the ladder is refused rather than cast. - A record's level is rounded toward the milder name (`35` becomes `WARN`), the opposite direction from `_normalize_threshold`: asking for a *threshold* of 35 must not silently admit warnings, but a record at 35 is a warning someone gave a custom number. - `propagate` is deliberately untouched, so a record still reaches the root logger as well. That keeps an interactive console readable and keeps `caplog.at_level(..., logger="simpler")` working — five test files assert on warnings that way. The host log is the complete copy; the console is a view of it. Turning propagation off would make the file the only destination and blind all of them. - The handler is installed where the threshold is seeded, not at import. `import simpler` has to keep working when `_task_interface` is missing or stale, which the build-stamp guard makes routine on every source-tree move until a rebuild, so putting the extension on the import path of the logging surface would lose the logger exactly when it is needed to explain why. Records logged before a worker is initialized stay on the root handler. - The handler swallows its own failures through `handleError`: a logging call must not become the reason a run fails. - Installation takes a module-level lock. `Worker.init()` and `ChipWorker.init()` hold per-instance locks, so nothing above serializes two instances initializing from different threads, and an unguarded check-and-add would let both add a handler and forward every record twice. Tests cover the forwarded level/func/message, that propagation and `caplog` survive, idempotent installation, the rounding direction, that a failing sink does not raise into its caller, and that `import simpler` installs nothing. One of them exists specifically because the others do not need it: every other test installs the handler itself, so without a test that `_initialize_host_log` installs it, the production line doing so could be deleted with the suite staying green. Verified by removing that line — exactly one test fails. hw-native-sys#1945 gave the host logger a configurable destination, so a run's Python records now join its C++ records in `<output_prefix>/host.<pid>.log`. That PR's own description of what stays on the console is corrected here in the same change: it said routing Python's records through the host logger was a separate change, which this is.
Python and C++ were two logging systems that agreed only on a threshold.
`Worker.init()` pushed the `simpler` logger's level into the native state, but a
Python record was then formatted by whatever handler sat on the root logger as
`[%(levelname)s] %(message)s` — no monotonic timestamp, no thread id. So a
Python record could not be ordered against a C++ one no matter where either was
written, and it went to the root logger's handler rather than to the host
logger's own output. The issue this belongs to is titled *one clock, one grammar,
one gate*; the Python side had the gate and neither of the others.
Seeding the native threshold now also installs a handler on the `simpler` logger
that forwards each record through `unified_log_*`, so every record in the process
shares one envelope, one clock and one destination.
- One new binding, `_emit_host_log(level, func, message)`, hands an
already-formatted message to `HostLogger::log`. The message is passed as a
`%s` argument, and a level outside the ladder is refused rather than cast.
- A record's level is rounded toward the milder name (`35` becomes `WARN`), the
opposite direction from `_normalize_threshold`: asking for a *threshold* of 35
must not silently admit warnings, but a record at 35 is a warning someone gave
a custom number.
- Forwarding is conditional on the host logger having a destination of its own.
It writes to stderr until a run gives it a directory, and the root logger's
handler already prints there, so forwarding unconditionally put one record on
one stream twice, in two envelopes, for every run that does not ask for
diagnostics. The check is per record because the directory arrives with a
run's config, after this handler is installed.
- `propagate` is deliberately untouched, so a record still reaches the root
logger as well. That keeps an interactive console readable and keeps
`caplog.at_level(..., logger="simpler")` working — five test files assert on
warnings that way. The host log is the complete copy; the console is a view of
it. Turning propagation off would make the file the only destination and blind
all of them.
- The handler is installed where the threshold is seeded, not at import.
`import simpler` has to keep working when `_task_interface` is missing or
stale, which the build-stamp guard makes routine on every source-tree move
until a rebuild, so putting the extension on the import path of the logging
surface would lose the logger exactly when it is needed to explain why.
Records logged before a worker is initialized stay on the root handler.
- The handler swallows its own failures through `handleError`: a logging call
must not become the reason a run fails.
- Installation takes a module-level lock. `Worker.init()` and `ChipWorker.init()`
hold per-instance locks, so nothing above serializes two instances
initializing from different threads, and an unguarded check-and-add would let
both add a handler and forward every record twice.
Tests cover the forwarded level/func/message, that nothing is forwarded while the
host log writes to stderr, that propagation and `caplog` survive, idempotent and
concurrent installation, the rounding direction, that a failing sink does not
raise into its caller, and that `import simpler` installs nothing. Their fixture
owns both the handler list and the logger level: this logger is process-global,
`configure_logging("null")` earlier in the same file leaves the level at `NUL`
without restoring it, and the suite's execution order is not the order the tests
are written in, so inheriting either one makes an assertion pass or fail by
position rather than by behaviour. One
of them exists specifically because the others do not need it: every other test
installs the handler itself, so without a test that `_initialize_host_log`
installs it, the production line doing so could be deleted with the suite
staying green. Verified by removing that line — exactly one test fails.
hw-native-sys#1945 gave the host logger a configurable destination, so a run's Python records
now join its C++ records in `<output_prefix>/host.<pid>.log`. That PR's own
description of what stays on the console is corrected here in the same change:
it said routing Python's records through the host logger was a separate change,
which this is.
Python and C++ were two logging systems that agreed only on a threshold.
`Worker.init()` pushed the `simpler` logger's level into the native state, but a
Python record was then formatted by whatever handler sat on the root logger as
`[%(levelname)s] %(message)s` — no monotonic timestamp, no thread id. So a
Python record could not be ordered against a C++ one no matter where either was
written, and it went to the root logger's handler rather than to the host
logger's own output. The issue this belongs to is titled *one clock, one grammar,
one gate*; the Python side had the gate and neither of the others.
Seeding the native threshold now also installs a handler on the `simpler` logger
that forwards each record through `unified_log_*`, so every record in the process
shares one envelope, one clock and one destination.
- One new binding, `_emit_host_log(level, func, message)`, hands an
already-formatted message to `HostLogger::log`. The message is passed as a
`%s` argument, and a level outside the ladder is refused rather than cast.
- A record's level is rounded toward the milder name (`35` becomes `WARN`), the
opposite direction from `_normalize_threshold`: asking for a *threshold* of 35
must not silently admit warnings, but a record at 35 is a warning someone gave
a custom number.
- Forwarding is conditional on the host logger having a destination of its own.
It writes to stderr until a run gives it a directory, and the root logger's
handler already prints there, so forwarding unconditionally put one record on
one stream twice, in two envelopes, for every run that does not ask for
diagnostics. The check is per record because the directory arrives with a
run's config, after this handler is installed.
- `propagate` is deliberately untouched, so a record still reaches the root
logger as well. That keeps an interactive console readable and keeps
`caplog.at_level(..., logger="simpler")` working — five test files assert on
warnings that way. The host log is the complete copy; the console is a view of
it. Turning propagation off would make the file the only destination and blind
all of them.
- The handler is installed where the threshold is seeded, not at import.
`import simpler` has to keep working when `_task_interface` is missing or
stale, which the build-stamp guard makes routine on every source-tree move
until a rebuild, so putting the extension on the import path of the logging
surface would lose the logger exactly when it is needed to explain why.
Records logged before a worker is initialized stay on the root handler.
- The handler swallows its own failures through `handleError`: a logging call
must not become the reason a run fails.
- Installation takes a module-level lock. `Worker.init()` and `ChipWorker.init()`
hold per-instance locks, so nothing above serializes two instances
initializing from different threads, and an unguarded check-and-add would let
both add a handler and forward every record twice.
Tests cover the forwarded level/func/message, that nothing is forwarded while the
host log writes to stderr, that propagation and `caplog` survive, idempotent and
concurrent installation, the rounding direction, that a failing sink does not
raise into its caller, and that `import simpler` installs nothing. Their fixture
owns both the handler list and the logger level: this logger is process-global,
`configure_logging("null")` earlier in the same file leaves the level at `NUL`
without restoring it, and the suite's execution order is not the order the tests
are written in, so inheriting either one makes an assertion pass or fail by
position rather than by behaviour. One
of them exists specifically because the others do not need it: every other test
installs the handler itself, so without a test that `_initialize_host_log`
installs it, the production line doing so could be deleted with the suite
staying green. Verified by removing that line — exactly one test fails.
#1945 gave the host logger a configurable destination, so a run's Python records
now join its C++ records in `<output_prefix>/host.<pid>.log`. That PR's own
description of what stays on the console is corrected here in the same change:
it said routing Python's records through the host logger was a separate change,
which this is.
2 participants
Summary
Add an opt-in, per-process buffered file sink for high-frequency host STRACE spans. Normal logs and the clock anchor remain on stderr, the encoded span grammar is unchanged, and setup or I/O failures fall back to stderr.
This removes per-span flushing to a shared stderr pipe from profiled multi-rank hot paths without changing native-run ownership, synchronization, or default runtime behavior.
Changes
host-strace.<pid>.logunderSIMPLER_HOST_STRACE_DIR, flushing at each completed root span.Verification
pre-commit run --files docs/dfx/host-trace.md src/common/log/host_log.cpp tests/ut/cpp/a5/test_host_log_off.cpp: all hooks passed, including clang-format, clang-tidy, cpplint, and markdownlint.cmake --build tests/ut/cpp/build -j8: passed onorigin/main@adf3764f.ctest --test-dir tests/ut/cpp/build -LE requires_hardware --output-on-failure: 115/115 passed (96no_hardwaretests).In the observed synchronous-stderr workload, individual 0.01-0.07 ms validation copies were separated by 10.10-18.44 ms unnamed host gaps at marker flush boundaries. With the per-PID sink, the direct four-rank run reduced runner-to-validate gap p95/max from 0.150/0.538 ms to 0.051/0.164 ms and validation max from 16.836 ms to 7.291 ms. This PR addresses that profiling observer effect only; it does not claim to fix the independent runtime lifecycle/scheduling issue tracked in hw-native-sys/pypto-serving#179.
Related to hw-native-sys/pypto-serving#179.