RFR: 8277617: Adjust AVX3Threshold for copy/fill stubs [v6]

[Sandhya Viswanathan]

On Tue, 30 Nov 2021 00:10:39 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> Currently 32-byte instructions are used for small array copy and clear. 
>> This can be optimized by using 64-byte instructions.
>> 
>> Please review.
>> 
>> Best Regards,
>> Sandhya
>
> Sandhya Viswanathan has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix whitespace

Yes, the patch doesn't change behavior on AVX2 and older AVX512 systems.

The additional performance numbers with the patch requested by Nils are as below:

Old AVX512
Before:

Benchmark                                    Mode  Cnt   Score   Error  Units
ArrayCopy.arrayCopyObject                    avgt    5  18.650 ± 2.773  ns/op
ArrayCopy.arrayCopyObjectNonConst            avgt    5  20.241 ± 1.398  ns/op
ArrayCopy.arrayCopyObjectSameArraysBackward  avgt    5  16.252 ± 0.076  ns/op
ArrayCopy.arrayCopyObjectSameArraysForward   avgt    5  15.965 ± 0.172  ns/op


After:

Benchmark                                    Mode  Cnt   Score   Error  Units
ArrayCopy.arrayCopyObject                    avgt    5  17.701 ± 2.623  ns/op
ArrayCopy.arrayCopyObjectNonConst            avgt    5  20.588 ± 0.775  ns/op
ArrayCopy.arrayCopyObjectSameArraysBackward  avgt    5  16.219 ± 0.066  ns/op
ArrayCopy.arrayCopyObjectSameArraysForward   avgt    5  15.937 ± 0.185  ns/op



AVX2
Before:

Benchmark                                    Mode  Cnt   Score   Error  Units
ArrayCopy.arrayCopyObject                    avgt    5  23.801 ± 0.090  ns/op
ArrayCopy.arrayCopyObjectNonConst            avgt    5  24.376 ± 0.867  ns/op
ArrayCopy.arrayCopyObjectSameArraysBackward  avgt    5  14.015 ± 0.016  ns/op
ArrayCopy.arrayCopyObjectSameArraysForward   avgt    5  15.355 ± 0.024  ns/op


After:

Benchmark                                    Mode  Cnt   Score   Error  Units
ArrayCopy.arrayCopyObject                    avgt    5  23.373 ± 0.629  ns/op
ArrayCopy.arrayCopyObjectNonConst            avgt    5  24.390 ± 0.875  ns/op
ArrayCopy.arrayCopyObjectSameArraysBackward  avgt    5  13.995 ± 0.056  ns/op
ArrayCopy.arrayCopyObjectSameArraysForward   avgt    5  15.383 ± 0.051  ns/op

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