RFR: 8329331: Intrinsify Unsafe::setMemory [v21]

Scott Gibbons sgibbons at openjdk.org
Tue Apr 16 17:50:45 UTC 2024


On Tue, 16 Apr 2024 00:04:15 GMT, Scott Gibbons <sgibbons at openjdk.org> wrote:

>> This code makes an intrinsic stub for `Unsafe::setMemory` for x86_64.  See [this PR](https://github.com/openjdk/jdk/pull/16760) for discussion around this change.
>> 
>> Overall, making this an intrinsic improves overall performance of `Unsafe::setMemory` by up to 4x for all buffer sizes.
>> 
>> Tested with tier-1 (and full CI).  I've added a table of the before and after numbers for the JMH I ran (`MemorySegmentZeroUnsafe`).
>> 
>> [setMemoryBM.txt](https://github.com/openjdk/jdk/files/14808974/setMemoryBM.txt)
>
> Scott Gibbons has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add enter() and leave(); remove Windows-specific register stuff

I ran the benchmark again using a branch from openjdk today against this modification.  Performance increased an average of 4.98x (max - 7.52x (unsafe 64-byte aligned), min - 3.02x (panama 255-byte aligned), stddev - 0.94x).

I'll integrate after a second review has been done.  Thanks!

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PR Comment: https://git.openjdk.org/jdk/pull/18555#issuecomment-2059637042


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