RFR: JDK-8300584: Accelerate AVX-512 CRC32C for small buffers [v2]

[Sandhya Viswanathan]

On Wed, 18 Jan 2023 23:10:12 GMT, Scott Gibbons <duke at openjdk.org> wrote:

>> Use AVX2 code for CRC32C for small buffers in the AVX-512 path.  Breakeven buffer size between the two algorithms is on the order of 384 bytes.
>> 
>> **Performance numbers for previous:**
>> 
>> Benchmark                    (count)   Mode  Cnt      Score     Error   Units
>> TestCRC32C.testCRC32CUpdate       64  thrpt    4  66974.957 ±   8.872  ops/ms
>> TestCRC32C.testCRC32CUpdate      128  thrpt    4  44224.810 ±  11.801  ops/ms
>> TestCRC32C.testCRC32CUpdate      256  thrpt    4  63997.611 ± 173.577  ops/ms
>> TestCRC32C.testCRC32CUpdate      512  thrpt    4  56068.683 ± 269.582  ops/ms
>> TestCRC32C.testCRC32CUpdate     2048  thrpt    4  27048.098 ±  87.350  ops/ms
>> TestCRC32C.testCRC32CUpdate    16384  thrpt    4   4066.736 ±  10.318  ops/ms
>> TestCRC32C.testCRC32CUpdate    65536  thrpt    4   1040.754 ±   6.419  ops/ms
>> 
>> 
>> **Performance numbers for this version:**
>> 
>> Benchmark                    (count)   Mode  Cnt       Score     Error   Units
>> TestCRC32C.testCRC32CUpdate       64  thrpt    3  161659.326 ±  74.974  ops/ms
>> TestCRC32C.testCRC32CUpdate      128  thrpt    3   88456.935 ±  11.940  ops/ms
>> TestCRC32C.testCRC32CUpdate      256  thrpt    3   73254.993 ±   5.004  ops/ms
>> TestCRC32C.testCRC32CUpdate      512  thrpt    3   56508.541 ± 298.229  ops/ms
>> TestCRC32C.testCRC32CUpdate     2048  thrpt    3   26701.995 ±  31.369  ops/ms
>> TestCRC32C.testCRC32CUpdate    16384  thrpt    3    4110.819 ±   4.618  ops/ms
>> TestCRC32C.testCRC32CUpdate    65536  thrpt    3    1045.821 ±   2.037  ops/ms
>
> Scott Gibbons has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Incorporate review comments

Looks good to me as well.

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Marked as reviewed by sviswanathan (Reviewer).

PR: https://git.openjdk.org/jdk/pull/12079