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docs: ObjectHeader::parse A/B after inlining the v1 message loop (at or below 8f59b2e)

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Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
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osobh
2026-09-27 23:15:09 -05:00
co-authored by Claude Opus 5.5
parent 05e1136027
commit 5b45c60c9c
3 changed files with 58 additions and 1 deletions
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BENCHMARKS.md
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@@ -500,6 +500,46 @@ explain the slower windows.
## Local file speed after range reads
### `ObjectHeader::parse` back at 8f59b2e's speed (2026-09-27, tank)
The remaining 4% (below) was the call to the version-1 message loop, which
`4313917` kept out of line with `#[inline(never)]`. Found with A/B builds
changing one piece at a time (perf is not available: `perf_event_paranoid`
4): `#[inline]` on `parse_v1_messages` alone brought
`object_header_parse_x401` from about 24.5–24.9 µs to 23.6–24.0 µs against
8f59b2e's 23.6–24.1 µs (short 4-second rounds); no attribute measured like
`#[inline(never)]`;
creating the chunk list only when a continuation is found measured no
faster on top and was not kept.
Same method as below: `8f59b2e` built in its own worktree and target
directory, separate binaries alternating, `taskset -c 5
local_metadata_bench --bench --warm-up-time 3 --measurement-time 10`, every
binary started with the 1-minute load average below 2 (0.19–1.86) and no
`rustc` running. Candidate: `96086ad` (this change). Median (range) of 3
rounds; run 2 also alternated `main` `425585e`.
| function | 8f59b2e | 425585e (main) | 96086ad | vs 8f59b2e |
|---|---:|---:|---:|---:|
| run 1: `object_header_parse_x401` | 23.81 µs (23.76–24.00) | | 23.57 µs (23.23–23.89) | **−1.0%** |
| run 1: `snod_parse_all` | 1.840 µs (1.837–1.854) | | 1.839 µs (1.837–1.873) | 0.0% |
| run 1: `btree_v1_walk` | 343 ns (338–349) | | 352 ns (344–363) | +2.7% |
| run 1: `facade_list_400_groups` | 8.03 ms (8.01–8.10) | | 8.05 ms (8.01–8.15) | +0.2% |
| run 2: `object_header_parse_x401` | 24.15 µs (23.74–24.41) | 24.93 µs (24.72–25.05) | 23.52 µs (23.34–23.68) | **−2.6%** |
| run 2: `snod_parse_all` | 1.843 µs (1.830–1.847) | 1.856 µs (1.850–1.865) | 1.861 µs (1.858–1.869) | +1.0% |
| run 2: `btree_v1_walk` | 346 ns (339–366) | 356 ns (347–356) | 357 ns (350–359) | +3.2% |
| run 2: `facade_list_400_groups` | 8.09 ms (8.02–8.10) | 8.12 ms (7.97–8.19) | 8.08 ms (7.98–8.12) | −0.1% |
- `ObjectHeader::parse` is at or below 8f59b2e (−1.0%, −2.6%) and 5.6%
faster than `main` in the same run.
- `btree_v1_walk` (one walk of a 350 ns B-tree) is 3% above 8f59b2e in
both runs, with overlapping ranges, and is the same on `main` (+0.2%
between `main` and this change): not from this change. The walk's code
changed in `e553153` (after a failed child the siblings are only read,
so the error returns after them; the fixture never takes that path, but
the loop carries the extra state); left as is.
- `snod_parse_all` and the facade listing are within noise.
### Local metadata and data reads after range-read M2/M3 (2026-09-27, tank)
`main` just before range-read M2/M3 (`8f59b2e`, PR #17) against `main`