Profiled the remaining lmxopcua#789 misses on windev, a VMware VM, using per-thread CPU and context-switch accounting
plus ETW CPU sampling.
- One blocking hand-off costs ~26 us of latency and ~18 us of CPU there, about 10x macOS.
- An idle evaluation makes four hand-offs in a row: host writer -> worker reader -> evaluation thread -> host reader
-> dispatcher.
- 48% of host CPU at 10k/s is in the kernel: the per-RunAsync NtWriteFile, thread-pool wakes, reads and waits.
Spin-before-block was measured at every hand-off and is not kept. It meets 150 us idle p50 (118 us) only by keeping
about two host cores and four worker cores busy for one stream. At 10k/s it reads +250 points.
Harness: new "paced 10,000/s, batched" row. It uses the same rate and keys, with each 1 ms tick submitted as one
RunBatch call, which is the production seams' shape. It runs after the original four phases, so their rows stay
comparable. On windev it halves host CPU, to +36..+45 points against +71..+84 unbatched. That is still above 25.
Design doc:
- 12.8: the record.
- 14 #15: the owner's decision on the Windows budgets. Recommended: measure on bare-metal Windows, then state the two
budgets per platform, with the batched row as the gate. The alternative is a shared-memory transport.
Claude-Session: https://claude.ai/code/session_01GT67ACmpMR7b9LGRPLijMi
The owner revised the per-shard worker idle RSS budget from 80 MB to 200 MB
+ scripts on 2026-11-11: compiles run in the worker, so Roslyn's code and
metadata stay resident (measured 159-187 MB) and no GC setting moves it.
The perf harness now reports both RSS rows against the 200 MB constant with
a PASS/MISS mark; A-3 records what the measurement showed.
Claude-Session: https://claude.ai/code/session_01GT67AD99zQQqpLCVm3p7xk
ShadowModeTests' runaway case asserted "slowest < 250 ms" around evaluations
whose timing included cold Roslyn compile/JIT of new script text, so it failed
on a healthy published path (540-880 ms measured, both SDK baselines).
The test now puts a test-owned barrier runner (GatedShadow) between the real
ShadowScriptRunner and the real worker pool. The runaway's first shadow run is
held before it reaches the pool, then (after it runs away in the worker, the
pool answers T and the worker is KilledDeadline with the runaway as culprit)
its outcome is held before comparison. Published evaluations made while a
barrier is closed must return the in-process values; a Mirror that waited for
its shadow hangs into a 30 s liveness failure (mutation-checked). Output
correctness, pool kill/quarantine, published-side never quarantined, the single
runaway mismatch (sibling is a victim, not compared) and key_busy drops are kept.
The wall-clock number moves to an opt-in Category=Perf case
(Shadow_published_path_latency_while_the_shadow_runs_away, OTOPCUA_SCRIPT_PERF=1)
on warmed evaluators, reporting hardware and load average.
Sibling: ContainmentTests' hard-deadline case timed the runaway's first
(cold-compile) run; it now compiles the runaway's source first with an input
that does not spin.
- IScriptRunner.RunBatch: one EvalBatch frame per worker for every evaluation ready to run; per-item, streamed results.
The default (InProcessScriptRunner) is RunAsync per item. Used by the Calculation pump (dequeue all, split at a
repeated tag, publish in dequeue order), the VirtualTag seam (ScriptBatchCoalescer, no timer) and the scripted-alarm
engine (whole dirty set). In process the pump and the engine stay one at a time, unchanged.
- Exact per-item deadlines: the worker hands work to an idle evaluation thread or defers it (EvalResults
deferred_eval_ids); the host stops that run's clock and restarts T then G when it starts (started_eval_ids). A run
queued behind a runaway is neither timed out nor struck and is a victim, not the culprit, at the kill.
- Scripted-alarm seam behind Scripting:Runner:Seams; unset Seams now means VirtualTag + Calculation, so alarms run out of
process only when listed. Load still compiles each predicate (to PE bytes only) so a broken one fails the load; passes
batch and apply in the serial order under the gate. Script faults freeze the condition BadInternalError; runner faults
freeze it BadResourceUnavailable and re-evaluate on recovery; a dead worker never clears an alarm. IScriptRunnerProvider
carries the runner to DriverHostActor.
- Perf harness: batch throughput (RunBatch vs RunAsync x n) and alarm-pass latency (in process / batched / serial);
design §12.3 records macOS + windev. On windev the serial out-of-process alarm pass misses 250 ms from ~500 alarms;
batched p99 <= 53 ms at 1,000.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
#789 (partial, further tuning deferred): combining inline frame writer, buffered
frame reader, one timer per evaluation for T and T+G, slot release on the reader
before the caller resumes, a non-spinning per-connection result dispatcher, and
blocking pipe I/O on Unix (both ends) so the socket never enters the socket
engine; TerminateJobObject kill on Windows. macOS host CPU at 10k evals/s K=2:
228-240 % -> 79 % (InProcess 69 %, IPC share +10 vs budget 25); windev 153 % ->
123 % (+115, still a miss). Harness reports the "vs InProcess" share, warm-cache
worker RSS, and times kill latency from the soft-timeout answer.
#790: the worker sends LoadStarted; the compile timeout is armed then, so a load
queued behind other compiles is never killed or struck.
#788: one Error with stack per down period, rate-limited Warnings with attempt
count, one Information on recovery.
Design doc §8.2 notes + §12.2 record.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
- A self-contained Host publish (-r win-x64 --self-contained, the Windows installs) now publishes the
ScriptWorker self-contained for the same RID into script-worker/. The launcher starts its apphost
directly when runtimeconfig.json lists includedFrameworks. A framework-dependent worker (docker-dev)
keeps running through the dotnet muxer.
- docker-dev/docker-compose.script-runner.yml: OutOfProcess for the central pair's VT + Calc seams.
Live drill recorded in design §12.1 (runaway kill + quarantine, kill -9 recovery, open circuit
with /health/ready still 200, metrics).
- ScriptRunnerPerfTests (Category=Perf, opt-in via OTOPCUA_SCRIPT_PERF=1): InProcess vs OutOfProcess
at K=1/2/4. The accepted 5k evals/s/node gate passes on macOS and windev. The host-CPU, RSS and
Windows latency budget misses are tracked as #789.
- Fix: the single-flight slot is released before the awaiting caller resumes. Before, a caller that
started its next run right after the previous one returned could be refused with "previous
evaluation still running", which the seams publish as Bad.
- Fix: the worker compiles on dedicated threads, not the thread pool. A burst of cold loads starved
the heartbeat, and the host killed the shard (found on windev). Load-timeout queueing is #790.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
Joseph Doherty