32 lines
1.3 KiB
Markdown
32 lines
1.3 KiB
Markdown
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# Measurement: the descriptor cache in internal/nfsfs
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- Date: 2026-09-22
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- Machine: AMD Ryzen AI Max+ Pro 395 (32 threads), idle
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- Toolchain: go1.27.1, no build flags
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- Command: `go test ./internal/nfsfs/ -run '^$' -bench=. -benchmem -count=5`
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## Baseline
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The commit b8758b7, the head of development before the descriptor cache: every
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READ, WRITE and SYNC opened the registered path, verified it with a stat and
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closed the descriptor again, per operation. The cache keeps idle descriptors of
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regular files in a bounded LRU and revalidates the identity on every use, so the
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measurements answer one question: what the open and close per operation cost.
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## Result
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Median of five runs, same session, same machine.
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| Benchmark | Baseline | With cache | Change |
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|---|---|---|---|
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| `BenchmarkRead64K` | 10888 ns/op | 9047 ns/op | -16.9 % |
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| `BenchmarkWrite64K` | 5881 ns/op | 5236 ns/op | -11.0 % |
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| `BenchmarkGetattr` | 461.4 ns/op | 437.2 ns/op | -5.2 % |
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| `BenchmarkLookup` | 1216 ns/op | 1134 ns/op | -6.7 % |
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The two data operations are the ones the cache touches, and they gain 11 to 17
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percent per operation. GETATTR and LOOKUP run the same code as before the cache
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(they resolve paths through Lstat either way), so their shifts are code layout
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noise of the same binary, not an effect to claim; both sit within the run to run
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spread the five repetitions showed.
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