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Back-to-back A/B on one machine: micro +85.9%, macro +56.6% msg/s; decode/hash byte volumes halved. Peak heap (getMaxMem) -21%/-20.7%. GC-sampling series shows retained-memory slope is workload-driven and unchanged between versions; the transient-copy reduction is not observable via occupied/total sawtooth under refc (deterministic frees, reused arena) and manifests as a lower absolute heap level, not a gentler slope. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
275 lines
11 KiB
Markdown
275 lines
11 KiB
Markdown
# Speed gain: pre-phase-2 vs post-phase-3 (same-session A/B)
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Rigorous before/after of the no-copy refactor chain, both branches built and run
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**back-to-back on the same machine, in the same session**, with identical build
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flags and an identical (temporary, uncommitted) GC-sampling patch to
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`apps/benchmarks/message_path_bench.nim`.
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## Methodology
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| Item | Value |
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|---|---|
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| Branch A ("pre-phase-2") | `experimental/chore-nocopy-e2e-perf-harness` @ `2a4da679` |
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| Branch B ("post-phase-3") | `experimental/chore-nocopy-wakuenvelop` @ `a6f1065a` |
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| Machine / OS | Apple M4, macOS (arm64) |
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| Nim | 2.2.4, `--mm:refc` |
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| Build flags (both) | `--mm:refc --cpu:arm64 --passC:"-arch arm64" --passL:"-arch arm64" -d:msgPathCounters -d:chronicles_log_level=ERROR --passL:librln_v2.0.2.a --passL:-lm` (copied from the `benchMessagePath` nimble task) |
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| Workload (both) | seed 42, payload mix 10/50/150 kB @ 25/50/25 %, N=1000 measured + 100 warmup |
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| Run order | A built+run (2 passes) → B built+run (3 passes; B pass 1 discarded, micro variance 5.51 % under a load spike to 13.8) |
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| Machine load | A passes: load avg ~3.3. B passes: elevated (8.9–13.8) — noted; the two accepted B passes have micro variance 3.34 % / 4.15 % (< 5 %). |
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**Sampling design (temporary patch, identical on both branches — only the relay
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handler signature differs between branches, which the sampling code does not
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touch):**
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- Micro loop and macro receive loop: every 50 messages record
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`(msg_index, getOccupiedMem(), getTotalMem())` into a pre-allocated buffer
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(no per-sample heap churn).
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- End of each scenario: `getMaxMem()` (process peak heap — the key single
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number) and `GC_getStatistics()`.
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- Existing `gc_collections` counter retained.
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- All raw outputs saved outside the repo; the patch was `git checkout --`
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discarded before switching branches (verified clean each time).
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The instrumented builds are byte-identical in decode/hash counters to the
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committed `bench_baseline.md` numbers, confirming the patch did not perturb the
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measured path.
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## Throughput — pre vs post
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Micro = single-node isolated receiver path; macro = two loopback nodes,
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publisher + archiving receiver. Micro msg/s is the mean of all accepted
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micro runs (A: 4 values across 2 passes; B: 4 values across 2 passes).
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| Scenario | Metric | Pre (A) | Post (B) | Gain |
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|---|---|---|---|---|
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| micro | msg/s (mean) | 1222.8 | 2273.7 | **+85.9 %** |
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| micro | ns/msg p50 | ~630 k | ~338 k | −46 % |
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| micro | ns/msg p99 | ~1.94 M | ~1.09 M | −44 % |
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| micro | decodes/msg | 2.000 | 2.000 | unchanged |
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| micro | hashes/msg | 2.000 | **1.000** | −50 % |
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| micro | hashed_MB | 130.00 | **65.00** | −50 % |
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| macro | msg/s (mean) | 225.45 | 353.1 | **+56.6 %** |
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| macro | ns/msg p50 | ~3.55 M | ~2.29 M | −36 % |
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| macro | ns/msg p99 | ~10.7 M | ~7.5 M | −30 % |
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| macro | decodes/msg | 6.000 | **3.000** | −50 % |
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| macro | hashes/msg | 5.000 | **3.000** | −40 % |
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| macro | decoded_MB / hashed_MB | 390.33 / 325.00 | **195.16 / 195.00** | ~−50 % |
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Raw CSV rows (accepted passes):
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```
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# A (pre-phase-2) — pass 1 / pass 2
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micro_run1,1000,834.793ms,1197.9,p50=640000,p99=1980291,dec=2.000,hash=2.000
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micro_run2,1000,803.157ms,1245.1,p50=618708,p99=1928250,dec=2.000,hash=2.000
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micro_run1,1000,835.163ms,1197.4,p50=642250,p99=1939583,dec=2.000,hash=2.000
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micro_run2,1000,799.486ms,1250.8,p50=621750,p99=1866667,dec=2.000,hash=2.000
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macro,1000,4431.571ms,225.7,p50=3552333,p99=10703625,dec=6.000,hash=5.000
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macro,1000,4441.265ms,225.2,p50=3580583,p99=10964584,dec=6.000,hash=5.000
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# B (post-phase-3) — pass 2 / pass 3 (pass 1 discarded, variance>5% under load)
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micro_run1,1000,451.768ms,2213.5,p50=345792,p99=1138042,dec=2.000,hash=1.000
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micro_run2,1000,436.666ms,2290.1,p50=335709,p99=1045417,dec=2.000,hash=1.000
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micro_run1,1000,445.048ms,2246.9,p50=340917,p99=1092750,dec=2.000,hash=1.000
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micro_run2,1000,426.569ms,2344.3,p50=329458,p99=1062291,dec=2.000,hash=1.000
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macro,1000,2884.679ms,353.0(pass2 353.0),p50=2276292,p99=7292208,dec=3.000,hash=3.000
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macro,1000,2831.619ms,353.2,p50=2304750,p99=8211292,dec=3.000,hash=3.000
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```
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The throughput win is driven by the removed redundant decodes/hashes (byte
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volumes halved), not by memory effects.
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## GC / heap analysis
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### Peak heap (`getMaxMem`, process-monotonic)
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| Scenario | Pre (A) | Post (B) | Δ |
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|---|---|---|---|
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| micro (first scenario, cleanest) | 333.60 MB | 263.61 MB | **−21.0 %** |
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| macro (whole-process peak) | 514.86 MB | 408.40 MB | **−20.7 %** |
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`gc_collections` (from `GC_getStatistics`): micro 7 / 8, macro 10 — **identical
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on both branches**. Same number of GC cycles; the new code simply sits at a
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lower occupied level at every point.
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### Heap-elevation series (occupied / total, MB)
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**Micro — no retention.** Occupied oscillates around a *flat* mean; `getTotalMem`
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(reserved arena) is dead-flat for the entire loop on both branches. There is **no
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elevation slope** in either — the transient decode/hash temporaries are allocated
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and freed between the 50-msg samples and the refc arena is reused in place.
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| msg idx | A occ | A total | B occ | B total |
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|---|---|---|---|---|
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| 0 | 275.50 | 333.60 | 207.07 | 263.61 |
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| 200 | 275.41 | 333.60 | 211.45 | 263.61 |
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| 400 | 274.67 | 333.60 | 208.16 | 263.61 |
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| 600 | 275.43 | 333.60 | 217.90 | 263.61 |
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| 800 | 274.36 | 333.60 | 208.91 | 263.61 |
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| 950 | 275.37 | 333.60 | 215.19 | 263.61 |
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- A occupied range 273.5–275.7 MB → **sawtooth amplitude ≈ 2.2 MB**.
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- B occupied range 207.1–217.9 MB → **sawtooth amplitude ≈ 10.8 MB**.
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- Both slopes ≈ 0 MB/100msg. Reserved total constant throughout.
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**Macro — archive retains all 1000 messages.** Occupied climbs monotonically
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(this is *retention*, the archive `SortedSet` accumulating messages), not
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transient churn.
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| msg idx | A occ | A total | B occ | B total |
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|---|---|---|---|---|
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| 50 | 308.66 | 414.61 | 235.78 | 329.06 |
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| 200 | 321.78 | 414.62 | 256.83 | 329.06 |
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| 400 | 353.13 | 414.64 | 283.56 | 329.07 |
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| 600 | 378.20 | 414.66 | 315.62 | 408.36 |
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| 800 | 405.33 | 414.85 | 336.89 | 408.38 |
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| 1000 | 428.25 | 514.86 | 361.54 | 408.40 |
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- Retention slope: A ≈ **12.6 MB / 100 msg**, B ≈ **13.2 MB / 100 msg** —
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statistically identical (same 1000 messages retained; payload bytes are
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retained identically under value vs ref semantics).
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- Reserved-arena growth: exactly **one** step each — A 414.6→514.8 MB at msg
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~650; B 329.1→408.4 MB at msg ~600.
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- The new code runs a **constant ~65–75 MB lower** at every sample and peaks
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20.7 % lower.
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<details><summary>Full CSV series (every 50 msgs; MB)</summary>
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```
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# scenario=micro_run1 branch=A(pre-2) idx,occMB,totMB
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0,275.50,333.60
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50,275.40,333.60
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100,273.50,333.60
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150,273.95,333.60
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200,275.41,333.60
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250,275.43,333.60
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300,275.41,333.60
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350,273.58,333.60
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400,274.67,333.60
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450,273.52,333.60
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500,275.41,333.60
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550,274.95,333.60
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600,275.43,333.60
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650,275.16,333.60
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700,275.43,333.60
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750,274.01,333.60
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800,274.36,333.60
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850,273.54,333.60
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900,275.70,333.60
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950,275.37,333.60
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# scenario=macro branch=A(pre-2) idx,occMB,totMB
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50,308.66,414.61
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100,313.30,414.61
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150,315.54,414.62
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200,321.78,414.62
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250,330.46,414.63
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300,345.20,414.63
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350,346.85,414.63
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400,353.13,414.64
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450,362.43,414.64
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500,376.96,414.65
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550,383.31,414.65
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600,378.20,414.66
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650,385.16,514.83
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700,395.89,514.84
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750,398.69,514.84
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800,405.33,514.85
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850,412.23,514.85
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900,423.95,514.85
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950,425.55,514.86
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1000,428.25,514.86
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# scenario=micro_run1 branch=B(post-3) idx,occMB,totMB
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0,207.07,263.61
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50,215.58,263.61
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100,209.58,263.61
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150,215.05,263.61
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200,211.45,263.61
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250,207.21,263.61
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300,217.89,263.61
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350,211.46,263.61
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400,208.16,263.61
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450,212.43,263.61
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500,215.31,263.61
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550,210.43,263.61
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600,217.90,263.61
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650,211.09,263.61
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700,212.69,263.61
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750,213.75,263.61
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800,208.91,263.61
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850,207.23,263.61
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900,214.70,263.61
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950,215.19,263.61
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# scenario=macro branch=B(post-3) idx,occMB,totMB
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50,235.78,329.06
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100,247.91,329.06
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150,250.84,329.06
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200,256.83,329.06
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250,261.66,329.06
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300,268.57,329.06
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350,277.31,329.07
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400,283.56,329.07
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450,290.08,329.08
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500,303.78,329.08
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550,306.02,329.08
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600,315.62,408.36
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650,315.92,408.37
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700,333.08,408.38
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750,330.20,408.38
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800,336.89,408.38
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850,346.05,408.39
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900,354.25,408.39
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950,359.48,408.40
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1000,361.54,408.40
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```
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</details>
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## Verdict on the hypothesis
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> Hypothesis: retained memory ~flat (temporary copies dominate), but the OLD
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> code shows a *faster heap-allocation elevation pattern* (steeper growth /
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> higher sawtooth amplitude / higher peak) than the new code.
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**(a) Retained memory flat? — CONFIRMED (as a between-version statement).**
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In micro there is no retention and occupied is flat on both branches. In macro
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the retention *slope* is essentially identical pre vs post (~12.6 vs ~13.2
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MB/100 msg) because the same 1000 messages are retained regardless of value-vs-
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ref semantics. Retained growth is a function of the workload, not the refactor.
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**(b) Allocation-elevation *slower* after the refactor? — NOT SUPPORTED by this
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instrumentation.** The occupied/total sampling shows:
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- Macro elevation slope is **unchanged** (retention-driven, not churn-driven).
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- Micro elevation slope is **zero on both**; if anything the micro sawtooth
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*amplitude* is larger post-refactor (10.8 MB vs 2.2 MB), the opposite of the
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hypothesis phrasing — but this is noise-level and the reserved arena is flat.
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The reason is the refc caveat: under `--mm:refc` the eliminated transient deep
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copies (async-closure env captures, Result/Option bind-outs, redundant decode
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buffers) are freed **deterministically** as each temporary leaves scope, and the
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arena pages are reused in place. `getTotalMem` is *peak reserved*, not
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*cumulative allocated*, so it plateaus once the arena is large enough; between
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two 50-msg samples the transient churn has already been allocated **and** freed.
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A coarse occupied/total sawtooth therefore **cannot** observe the transient-copy
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reduction — and `gc_collections` is identical (10/10), reinforcing this.
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**What the data *does* prove about memory:** the refactor lowers the **absolute
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heap level** — peak heap −21 % (micro) / −20.7 % (macro), and a constant
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~65–75 MB lower occupied baseline throughout the macro run. That is a real,
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measurable memory win (fewer live temporaries at any instant, plus half the hash
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buffers). It manifests as a **lower constant offset**, not a gentler slope or
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smaller sawtooth.
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**What *would* detect the transient-copy reduction directly:** a cumulative
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bytes-allocated counter (instrumenting the Nim allocator or exposing
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`GC_getStatistics` cumulative fields), or malloc-level profiling (macOS
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Instruments Allocations, `heaptrack`, or valgrind `massif`), or a peak-RSS probe
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under memory pressure. The current harness exposes none of these — a harness
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gap, not a missing win.
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## Bottom line
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| Claim | Result |
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|---|---|
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| Throughput up | **micro +85.9 %, macro +56.6 %** |
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| Redundant decode/hash removed | hashes/msg −50 % micro, decode+hash −40–50 % macro (byte-exact) |
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| Peak heap down | **−21 % / −20.7 %** |
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| Retained-memory slope changed by refactor | No (retention is workload-driven, identical) |
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| Old code shows steeper allocation elevation | Not observable via occupied/total sampling under refc; win is a level shift, not a slope |
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