perf(order_book): use try_emplace for baseline price levels#138
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The flamegraph's hot _Rb_tree::_M_emplace_unique + pmr allocation is in the
baseline OrderBook::level_for: std::map::emplace(price, Level{...}) allocates a
map node and constructs the value *before* checking for a duplicate key, then
frees the node when the price level already exists. With a bounded price band the
levels almost always already exist in steady state, so every resting order paid a
wasted pmr node alloc+free.
try_emplace (C++17) does not allocate or construct when the key is present — the
intrusive store already uses it; this brings the baseline path in line. Semantics
are identical: an absent level is still inserted empty with the map's pmr
resource (scoped-allocator propagation), and erase_level_if_empty still prunes it,
so best_bid/best_ask and the "no empty levels" invariant are unchanged.
Measured A/B (Release -O3, baseline storage, qsl-bench profile 3s, same host,
5 runs each, non-overlapping ranges): ~8.03M -> ~8.46M ops/sec, ~+5%.
Determinism preserved: fixtures byte-identical across g++/clang++ and vs the
committed copies; OCaml differential passes. make check/asan 265/265.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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#139) Refreshes the committed flamegraph so its Source digest matches current src/ (PRs #136 #137 #138; Dirty inputs: no). The try_emplace optimization (#138) is visible: the previously top-3 std::_Rb_tree::_M_emplace_unique allocation frame (~1137 samples) is gone from the hot stacks, which are now the actual matching work — cancel, match_baseline, rest, new_limit. ~20k samples, zero [unknown]. Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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…ct (#147) * docs: overhaul all stale docs for the post-v0.2.1 (v0.2.2) state Full staleness audit of every prose doc against current main. The anchors were frozen at v0.2.1 / 263 tests / "no active milestone" while 12 PRs (#135-#146) had merged and are unreleased. - Resume anchors (PROGRESS.md, HANDOFF.md): Current state / Last action / Next action / test count (263->270) brought current; the two duplicate frozen anchors and the stale macOS benchmark numbers fixed; a dated v0.2.2 log entry. - CLAUDE.md + AGENTS.md: the post-M35 roadmap-memory section now records the post-v0.2.1 hardening + perf wave (identical edit in both). - CHANGELOG.md: new [0.2.2] section (decoder enum rejection #136, network/CLI hardening #137/#140/#141/#143, real UBSan abort gate #142, ocaml diff_report #144, try_emplace ~+5% #138, index load-factor ~+18.6% #145). CMakeLists version 0.2.1 -> 0.2.2. - README: benchmark/flamegraph/limitations sections reflect the engine wins (measured on the profile workload, not the micro-bench table) and the gateway hardening; release_readiness 270/270 + UBSan gate + v0.2.2 scope. - Networking docs (socket_gateway, socket_hardening): connection cap, EINTR retry, transient-accept survival, fd-exhaustion handling, UDP send-error counting. replay_and_recovery: decode_command now rejects out-of-domain enums. binary_protocol/differential_testing/fix_protocol/SECURITY/recruiting_notes/ CONTRIBUTING: smaller accuracy updates. results/README: add the three socket artifacts. make check 270/270. Stale results/*.txt provenance digests regenerated separately. pool_backed_storage.md table follows its artifact regeneration. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * results: regenerate stale provenance artifacts for the v0.2.2 source The post-v0.2.1 source changes (#135-#146) left 14 results/*.txt with stale Source digests (the authoritative staleness signal per the provenance rules, not commit-hash drift). Regenerated via their make targets so each declares Dirty inputs: no against current HEAD: differential, pool_backed_storage, allocator_experiment, recovery_benchmarks, false_sharing_study, perf_stat_linux (partial PMU, QSL_PERF_ALLOW_PARTIAL), perf_report_linux, numa_affinity_study (linux-constrained), socket_load_summary, socket_profile_loopback, socket_stress_summary, dpdk_environment, nic_offload_environment. docs/pool_backed_storage.md: refreshed the median table, digest reference, and qualitative ordering from the regenerated artifact (contiguous fastest on four of five workloads; intrusive leads dense). The baseline rows now include the try_emplace (#138) and index load-factor (#145) wins. Honesty notes: these were measured on a thermally-warmed M2 from a long session, so absolute values run higher than a cool-host snapshot — the relative orderings and provenance digests are the load-bearing content, and every artifact carries a hardware/build-dependence caveat. latest.txt is regenerated separately on a cooled host to keep its headline micro-benchmark numbers representative. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * results: regenerate latest.txt (cool host) and sync README/PROGRESS numbers latest.txt regenerated on a thermally-recovered host so the headline micro-bench numbers are representative (protocol canary 16.1 ns/op), with a fresh Source digest (Dirty inputs: no) matching current source. The README benchmark table and the PROGRESS measured-results section are aligned to it: order_book ~90, protocol ~16, gateway ~102, matching ~91, replay ~101 ns. The matching/replay rows are slightly faster than the prior committed run (the v0.2.2 engine wins showing on the resting-order paths); the order_book micro-bench is unchanged (near-empty index, so it does not exercise the load-factor win). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * results: re-regenerate env-check artifacts against the final v0.2.2 docs dpdk_environment.txt and nic_offload_environment.txt include README.md (and CLAUDE.md/AGENTS.md/results/README.md) in their digest scope, so the README number-sync re-staled them. Regenerated against the final committed docs; Dirty inputs: no. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> --------- Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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…e wins (#148) Adds the missing performance-evidence report. Profiles the matching-engine hot path with Linux perf + flamegraphs on ARM64 (Apple M2, Fedora Asahi), confirms order-book insertion + matching dominate, and documents the before -> after change in latency, throughput, and CPU counters for the two v0.2.2 optimizations (#138 try_emplace level_for, #145 index load-factor 0.25). Headline (qsl-perfeval, steady-state deep book, baseline storage, Release): throughput 8.89M -> 11.13M orders/sec (+25.2%) p99 latency 250ns -> 208ns (-16.8%) cycles/order 348.2 -> 288.4 (-17.2%) instr/order 1239 -> 1143 (-7.8%); IPC 3.56 -> 3.96 branch-miss 2.02% -> 1.81% allocs/order 1.106 -> 1.106 (UNCHANGED) cache-miss unavailable (Apple Silicon PMU lacks cache counters; #90) Honesty: the counters correct the original #138 rationale — the win is fewer cycles/instructions per order (shorter hash probe chains + no throwaway per-insert pmr::list construction), NOT fewer allocations (libstdc++ map::emplace checks the key before allocating). Latency includes ~12ns steady_clock overhead (reported); cache-miss rate is reported unavailable, never estimated. New tooling: - apps/qsl-perfeval: a dedicated evidence harness (separate binary so its global operator-new alloc counter + per-op timing cannot perturb qsl-bench/latest.txt). Reports orders/sec, mean/p50/p99 latency, allocations/order; run under perf stat/record for counters + flamegraphs. - docs/performance/{before,after}.svg (perf call-graph flamegraphs), docs/performance/perf-stat.txt (raw counters + metadata + #90 caveat). - qsl_perfeval_smoke CTest. make check/asan 271/271; CodeScene clean; determinism unaffected (no engine change here). Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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Summary
Flamegraph-driven optimization of the hot path. The flamegraph's hot
std::_Rb_tree::_M_emplace_unique+ pmr allocation sits in the baselineOrderBook::level_for:bids_.emplace(price, Level{...}); // beforestd::map::emplaceallocates a map node and constructs the value before checking for a duplicate key, then frees the node when the price level already exists. With a bounded price band the levels almost always already exist in steady state, so every resting order paid a wasted pmr node alloc+free.try_emplace(C++17) does not allocate or construct when the key is present:bids_.try_emplace(price); // afterThe intrusive store already uses
try_emplace(append_resting/itslevel_for); this brings the baseline path in line.Why it's safe (determinism preserved)
Semantics are identical: an absent level is still inserted empty with the map's pmr resource (scoped-allocator propagation — no explicit allocator arg needed), and
erase_level_if_emptystill prunes emptied levels, sobest_bid/best_askand the "no empty levels" invariant are unchanged.make check265/265,make asan265/265.Measured win (controlled A/B)
Release
-O3, baseline storage,qsl-bench profile 3(the steady-state deep-book workload the flamegraph profiles), same host, back-to-back, 5 runs each:emplace)try_emplace)Non-overlapping ranges → ~+5% throughput, real (not noise). Back-to-back A/B controls for machine load.
Why
results/latest.txtis unchangedThe committed micro-benchmark
order_book add/mod/cancelchurns single-order levels (each cancel empties the level, so the next add re-creates it → the key is absent every time andtry_emplacecannot help), so it does not exercise the optimized existing-level fast path. The win is on the steady-state path with multiple orders per level. Regeneratinglatest.txtwould only inject run-to-run variance (verified: a quiet-canary run leaves those scenarios within noise), so it is intentionally left at its quiet-machine snapshot rather than presenting variance as change.🤖 Generated with Claude Code