feat(io): add REST performance instrumentation - #178
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Adds a perf_instrumentation config gate (off by default; no hot-path clock reads when off), per-request timing carriers on rest_chunked_rx_request, and a host_read_attribution tag so synchronous host reads can be told apart from async chunk reads. prep_host_rx_request gains a four-argument overload carrying the tag; the existing three-argument signature stays as a delegating overload, so no existing symbol or caller changes.
…ation Adds the REST perf-counter subsystem: a 16-field rest_perf_snapshot value struct, per-reactor relaxed atomics behind it, and a pool-level aggregation on rest_ioctx (sums, maxes, and the smallest non-zero ttfb). Retry, terminal-failure, device-stream-sync and payload-byte counters are always on; the micro timings (chunk_get, queue_wait, ttfb, h2d_observed) record only under the perf_instrumentation gate, which costs zero clock reads when off. Snapshot layout is not ABI-stable: consumers build from the same source pin, and fields are appended, never reordered or removed.
A real 127.0.0.1 HTTP/1.1 server for driving the REST reactor end to end in-process: ranged GET/206, HEAD, a single-page LIST XML mode, a controllable per-request delay, and fault injection (fail the first N requests with a configurable status). Pure POSIX + std, header-only.
Twenty cases on cucascade_io_tests locking the perf-counter contract: default/zero state and noexcept readouts, chunk vs blocking vs footer attribution, HEAD and LIST isolation from payload/chunk counters, gate on/off semantics (safety counters live with the gate off), pool aggregation across reactors, retry/terminal accounting incl. the 403 re-authorize path, device-read h2d timings with a clean-read stream-sync-zero proof, deterministic queue wait, and a stash-hit zero-movement check. Driven through the loopback range server; snapshots are read only after all futures resolve (counters are relaxed atomics).
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/ok to test 3eda942 |
aminaramoon
approved these changes
Aug 3, 2026
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What
Implements the REST perf-instrumentation follow-up left out of #172. Sirius consumes these counters in its S3 tests and benchmark JSON.
Add loopback HTTP range server for REST conformance tests
Counter behavior
chunk_get,queue_wait,h2d_observed,blocking_host_get, andttfb_nsare recorded only whenperf_instrumentationis enabled. The disabled instrumentation path adds no clock reads.ttfb_nsmeasures GET submission to completion of the first completed GET, not time to the first byte on the wire.rest_perf_snapshotis source-pin API rather than a stable binary layout. New fields are appended without reordering existing fields.Validation
pixi run -e cuda-12-stable build/test— 4/4 ctest targets,cucascade_io_tests103 cases / 1169 assertions green,[rest][perf]20 cases / 149 assertions.