Reduce variance in sort benchmarks by reusing temp file #8939
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Locale benchmarks were creating temp files inside the bench loop (from d1cd999), causing filesystem noise and false CodSpeed regressions. The same commit's sort_bench.rs got it right with file creation outside the loop. This fix aligns with that pattern.
CodSpeed Performance ReportMerging #8939 will degrade performances by 3.36%Comparing Summary
Benchmarks breakdown
Footnotes
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GNU testsuite comparison: |
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Bug existed since Sept 2024 but variance was below CodSpeed's threshold (~1-3%). On Oct 11, CI changed to run 19 benchmarks in parallel (f19d7ec, 6df73f0) instead of sequentially. This amplified
/tmpcontention, pushing variance to 2.64%—above detection threshold. The parallel execution exposed what was always there.Solution
Move
NamedTempFile::new()outside loop, matchingsort_bench.rspattern:Eliminates filesystem noise while preserving correct semantics (sort overwrites file each iteration, no caching)
Notes
Affected PRs: #8935, #8936, #8927, #8926, #8930, #8932.