RFR: 8365290: [perf] x86 ArrayFill intrinsic generates SPLIT_STORE for unaligned arrays [v4]

[Vladimir Ivanov]

On Sat, 30 Aug 2025 16:04:00 GMT, Vladimir Ivanov <vaivanov at openjdk.org> wrote:

>> On the SRF platform for runs with intrinsic scores for the ArrayFill test reports ~2x drop for several sizes due to a lot of the 'MEM_UOPS_RETIRED.SPLIT_STORES' events. The 'good' case for the ArraysFill.testCharFill with size=8195 reports numbers like
>> MEM_UOPS_RETIRED.SPLIT_LOADS | 22.6711
>> MEM_UOPS_RETIRED.SPLIT_STORES | 4.0859
>> while for 'bad' case these metrics are
>> MEM_UOPS_RETIRED.SPLIT_LOADS | 69.1785
>> MEM_UOPS_RETIRED.SPLIT_STORES | 259200.3659
>> 
>> With alignment on the cache size no score drops due to split_stores but small reduction may be reported due to extra 
>> SRF 6740E | Size | orig | pathed | pO/orig
>> -- | -- | -- | -- | --
>> ArraysFill.testByteFill | 16 | 152031.2 | 157001.2 | 1.03
>> ArraysFill.testByteFill | 31 | 125795.9 | 177399.2 | 1.41
>> ArraysFill.testByteFill | 250 | 57961.69 | 120981.9 | 2.09
>> ArraysFill.testByteFill | 266 | 44900.15 | 147893.8 | 3.29
>> ArraysFill.testByteFill | 511 | 61908.17 | 129830.1 | 2.10
>> ArraysFill.testByteFill | 2047 | 32255.51 | 41986.6 | 1.30
>> ArraysFill.testByteFill | 2048 | 31928.97 | 42154.3 | 1.32
>> ArraysFill.testByteFill | 8195 | 10690.15 | 11036.3 | 1.03
>> ArraysFill.testIntFill | 16 | 145030.7 | 318796.9 | 2.20
>> ArraysFill.testIntFill | 31 | 134138.4 | 212487 | 1.58
>> ArraysFill.testIntFill | 250 | 74179.23 | 79522.66 | 1.07
>> ArraysFill.testIntFill | 266 | 68112.72 | 60116.49 | 0.88
>> ArraysFill.testIntFill | 511 | 39693.28 | 36225.09 | 0.91
>> ArraysFill.testIntFill | 2047 | 11504.14 | 10616.91 | 0.92
>> ArraysFill.testIntFill | 2048 | 11244.71 | 10969.14 | 0.98
>> ArraysFill.testIntFill | 8195 | 2751.289 | 2692.216 | 0.98
>> ArraysFill.testLongFill | 16 | 212532.5 | 212526 | 1.00
>> ArraysFill.testLongFill | 31 | 137432.4 | 137283.3 | 1.00
>> ArraysFill.testLongFill | 250 | 43185 | 43159.78 | 1.00
>> ArraysFill.testLongFill | 266 | 42172.22 | 42170.5 | 1.00
>> ArraysFill.testLongFill | 511 | 23370.15 | 23370.86 | 1.00
>> ArraysFill.testLongFill | 2047 | 6123.008 | 6122.73 | 1.00
>> ArraysFill.testLongFill | 2048 | 5793.722 | 5792.855 | 1.00
>> ArraysFill.testLongFill | 8195 | 616.552 | 616.585 | 1.00
>> ArraysFill.testShortFill | 16 | 152088.6 | 265646.1 | 1.75
>> ArraysFill.testShortFill | 31 | 137369.8 | 185596.4 | 1.35
>> ArraysFill.testShortFill | 250 | 58872.03 | 99621.15 | 1.69
>> ArraysFill.testShortFill | 266 | 91085.31 | 93746.62 | 1.03
>> ArraysFill.testShortFill | 511 | 65331.96 | 78003.83 | 1.19
>> ArraysFill.testShortFill | 2047 | 21716.32 | 21216.81 | 0.98
>> ArraysFill.testShortFill...
>
> Vladimir Ivanov has updated the pull request incrementally with one additional commit since the last revision:
> 
>   JDK-8365290 [perf] x86 ArrayFill intrinsic generates SPLIT_STORE for unaligned arrays

Later alignment improve performance a little bit. Current numbers are:
SRF | size | jdk26 | patched with "+optFill" | patched/jdk26
ArraysFill.testByteFill | 16 | 151937.634 | 175045.819 | 1.15
ArraysFill.testByteFill | 31 | 125661.092 | 211226.668 | 1.68
ArraysFill.testByteFill | 250 | 57599.684 | 123670.638 | 2.15
ArraysFill.testByteFill | 266 | 44617.505 | 147306.352 | 3.30
ArraysFill.testByteFill | 511 | 61541.499 | 129234.48 | 2.10
ArraysFill.testByteFill | 2047 | 32073.997 | 41503.438 | 1.29
ArraysFill.testByteFill | 2048 | 31729.263 | 41977.271 | 1.32
ArraysFill.testByteFill | 8195 | 10620.363 | 10911.334 | 1.03
ArraysFill.testIntFill | 16 | 144924.577 | 264101.45 | 1.82
ArraysFill.testIntFill | 31 | 128877.207 | 211225.233 | 1.64
ArraysFill.testIntFill | 250 | 73785.182 | 79204.674 | 1.07
ArraysFill.testIntFill | 266 | 67703.171 | 75436.831 | 1.11
ArraysFill.testIntFill | 511 | 39489.095 | 36011.078 | 0.91
ArraysFill.testIntFill | 2047 | 11431.835 | 10509.545 | 0.92
ArraysFill.testIntFill | 2048 | 11178.661 | 10882.991 | 0.97
ArraysFill.testIntFill | 8195 | 2629.065 | 2601.19 | 0.99
ArraysFill.testLongFill | 16 | 211218.892 | 211250.585 | 1.00
ArraysFill.testLongFill | 31 | 133026.186 | 137374.876 | 1.03
ArraysFill.testLongFill | 250 | 42907.745 | 42937.988 | 1.00
ArraysFill.testLongFill | 266 | 41935.645 | 41920.801 | 1.00
ArraysFill.testLongFill | 511 | 23217.606 | 23227.904 | 1.00
ArraysFill.testLongFill | 2047 | 6083.099 | 6083.384 | 1.00
ArraysFill.testLongFill | 2048 | 5751.203 | 5753.409 | 1.00
ArraysFill.testLongFill | 8195 | 612.17 | 612.634 | 1.00
ArraysFill.testShortFill | 16 | 151917.079 | 352122.571 | 2.32
ArraysFill.testShortFill | 31 | 138000.217 | 226271.221 | 1.64
ArraysFill.testShortFill | 250 | 58641.362 | 99043.571 | 1.69
ArraysFill.testShortFill | 266 | 90499.649 | 93200.335 | 1.03
ArraysFill.testShortFill | 511 | 64958.462 | 77930.734 | 1.20
ArraysFill.testShortFill | 2047 | 21577.954 | 21210.006 | 0.98
ArraysFill.testShortFill | 2048 | 21538.005 | 21429.382 | 0.99
ArraysFill.testShortFill | 8195 | 5883.097 | 5775.499 | 0.98

-------------

PR Comment: https://git.openjdk.org/jdk/pull/26747#issuecomment-3242746861