RFR: 8277617: Adjust AVX3Threshold for copy/fill stubs

[Jie Fu]

On Wed, 1 Dec 2021 03:38:00 GMT, Jie Fu <jiefu at openjdk.org> wrote:

>>> @dholmes-ora We see about 25% gain on a micro on our latest platform. There is no cpuid bit for this, so the closest was to check for the new serialize ISA supported on this platform.
>> 
>> It would be better to add a jmh test for this opt.
>> Thanks.
>
>> @DamonFool There are jmh tests for Arraycopy in test/micro/org/openjdk/bench/java/lang/Arraycopy.java.
> 
> So how about posting the detailed perf data before and after this patch?
> Thanks.

> > > @DamonFool There are jmh tests for Arraycopy in test/micro/org/openjdk/bench/java/lang/Arraycopy.java.
> > 
> > 
> > So how about posting the detailed perf data before and after this patch? Thanks.
> 
> Before: Benchmark Mode Cnt Score Error Units ArrayCopy.arrayCopyObject avgt 5 19.538 ± 0.073 ns/op ArrayCopy.arrayCopyObjectNonConst avgt 5 20.513 ± 0.104 ns/op ArrayCopy.arrayCopyObjectSameArraysBackward avgt 5 15.919 ± 0.652 ns/op ArrayCopy.arrayCopyObjectSameArraysForward avgt 5 15.669 ± 0.359 ns/op
> 
> After: Benchmark Mode Cnt Score Error Units ArrayCopy.arrayCopyObject avgt 5 16.957 ± 0.584 ns/op ArrayCopy.arrayCopyObjectNonConst avgt 5 17.221 ± 0.036 ns/op ArrayCopy.arrayCopyObjectSameArraysBackward avgt 5 12.952 ± 0.068 ns/op ArrayCopy.arrayCopyObjectSameArraysForward avgt 5 13.562 ± 0.124 ns/op

Thanks @sviswa7 for your sharing.
So the performance number looks good on Intel's latest AVX512 platform.

We don't use the 64-byte instructions as default on Intel's old AVX512 platforms, right?
If so, is it possible a performance regression for the old platforms after this patch?
Thanks.

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PR: https://git.openjdk.java.net/jdk/pull/6512