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by andyayers 444 days ago
Long-running methods (like the one here) transition mid-execution to more optimized versions, via on-stack replacement (OSR), after roughly 50K iterations. So you end up running optimized code either if the method is called a lot or loops frequently.

The OSR transition happens here, but between .net8 and .net9 some aspects of loop optimizations in OSR code regressed.
1 comments
Dylan16807 444 days ago
So there actually was a regression and it wasn't an intentional warmup delay?
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andyayers 444 days ago
There indeed is a regression if the method is only called a few times. But not if it is called frequently.

With BenchmarkDotNet it may not be obvious which scenario you intend to measure and which one you end up measuring. BDN runs the benchmark method enough times to exceed some overall "goal" time for measuring (250 ms I think). This may require many calls or may just require one.

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