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perf: Cache Version hash value in dedicated slot#1118

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notatallshaw merged 3 commits intopypa:mainfrom
notatallshaw:perf/cache-hash-value
Mar 13, 2026
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perf: Cache Version hash value in dedicated slot#1118
notatallshaw merged 3 commits intopypa:mainfrom
notatallshaw:perf/cache-hash-value

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@notatallshaw notatallshaw commented Mar 11, 2026

I'm surprised CPython isn't doing this automatically? But this appeared to make a difference locally.

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notatallshaw commented Mar 11, 2026

Faster warm hash:

| -        | 283±5μs              | 169±0.5μs           |    0.6  | version.TimeVersionSuite.time_hash_warm [runnervm0kj6c/virtualenv-py3.10-PYTHONHASHSEED0]              |
| -        | 210±3μs              | 108±1μs             |    0.51 | version.TimeVersionSuite.time_hash_warm [runnervm0kj6c/virtualenv-py3.11-PYTHONHASHSEED0]              |
| -        | 218±5μs              | 130±0.9μs           |    0.6  | version.TimeVersionSuite.time_hash_warm [runnervm0kj6c/virtualenv-py3.12-PYTHONHASHSEED0]              |
| -        | 235±2μs              | 137±2μs             |    0.58 | version.TimeVersionSuite.time_hash_warm [runnervm0kj6c/virtualenv-py3.13-PYTHONHASHSEED0]              |
| -        | 181±7μs              | 130±2μs             |    0.72 | version.TimeVersionSuite.time_hash_warm [runnervm0kj6c/virtualenv-py3.14-PYTHONHASHSEED0]              |
| -        | 334±2μs              | 223±2μs             |    0.67 | version.TimeVersionSuite.time_hash_warm [runnervm0kj6c/virtualenv-py3.8-PYTHONHASHSEED0]               |
| -        | 315±4μs              | 200±1μs             |    0.63 | version.TimeVersionSuite.time_hash_warm [runnervm0kj6c/virtualenv-py3.9-PYTHONHASHSEED0]               |

Interestingly this moves Python 3.11 into the lead for fastest warm hash, most microbenchmarks show Python 3.14 in the lead at everything.

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notatallshaw commented Mar 12, 2026

I think this change might actually make the warm Version hash benchmark fairly pointless, I doubt we can ever get faster than a slotted cache look up.

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henryiii commented Mar 12, 2026

We can drop it later, would be nice to at least get a plot of it over time first.

@notatallshaw notatallshaw force-pushed the perf/cache-hash-value branch from 1576e48 to 2393a78 Compare March 12, 2026 23:20
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henryiii commented Mar 13, 2026

I doubt we can ever get faster

Makes it faster...

@notatallshaw notatallshaw merged commit 1676a10 into pypa:main Mar 13, 2026
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ngoldbaum pushed a commit to ngoldbaum/packaging that referenced this pull request Apr 1, 2026
@notatallshaw @ngoldbaum
perf: Cache Version hash value in dedicated slot (pypa#1118)
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