RFR: 8350093: RISC-V: java/math/BigInteger/LargeValueExceptions.java timeout with COH

[Feilong Jiang]

On Fri, 14 Feb 2025 13:21:58 GMT, Fei Yang <fyang at openjdk.org> wrote:

> Hi, please review this change resolving a timeout issue in `LargeValueExceptions.squareDefiniteOverflow()`.
> 
> This issue only happens on platforms with slow unaligned memory accesses like Unmatched or Premier-P550 SBCs.
> Async profiler shows major time was spent in multiplyToLen stub code. When AvoidUnalignedAccesses is enabled,
> there is a simple alignment check, which assumes 8-byte alignment for base_offset of int arrays. But this is
> not the case with COH: base_offset is 12 bytes instead of 16 bytes for int arrays.
> 
> Patch simply makes it explicit about the requirement of base_offset. Sanity tested on Premier P550.
> No obvious change witnessed on JMH after this change:
> 
> -----------------------------------------------------------------------------------------------
> 
> Without COH:
> 
> Benchmark                               (maxNumbits)  Mode  Cnt        Score      Error  Units
> BigIntegers.SmallShifts.testLeftShift             32  avgt   15      138.939 ±    2.246  ns/op
> BigIntegers.SmallShifts.testLeftShift            128  avgt   15       88.391 ±    1.210  ns/op
> BigIntegers.SmallShifts.testLeftShift            256  avgt   15      117.590 ±    1.398  ns/op
> BigIntegers.SmallShifts.testRightShift            32  avgt   15      150.338 ±    1.961  ns/op
> BigIntegers.SmallShifts.testRightShift           128  avgt   15      104.540 ±    5.636  ns/op
> BigIntegers.SmallShifts.testRightShift           256  avgt   15      126.082 ±    1.756  ns/op
> BigIntegers.testAdd                              N/A  avgt   15       97.513 ±   40.746  ns/op
> BigIntegers.testGcd                              N/A  avgt   15  5409222.706 ± 5934.667  ns/op
> BigIntegers.testHugeLargeDivide                  N/A  avgt   15      246.904 ±    1.552  ns/op
> BigIntegers.testHugeSmallDivide                  N/A  avgt   15      248.997 ±    1.374  ns/op
> BigIntegers.testHugeToString                     N/A  avgt   15     2421.432 ±   62.208  ns/op
> BigIntegers.testLargeSmallDivide                 N/A  avgt   15      216.859 ±    1.760  ns/op
> BigIntegers.testLargeToString                    N/A  avgt   15      425.653 ±   13.305  ns/op
> BigIntegers.testLeftShift                        N/A  avgt   15     2265.137 ±   24.319  ns/op
> BigIntegers.testMultiply                         N/A  avgt   15    15862.412 ±  417.880  ns/op <========
> BigIntegers.testRightShift                       N/A  avgt   15      936.071 ±   15.247  ns/op
> BigIntegers.testSmallToString                    N/A  avgt   15      322.350 ±   16.075...

Looks good, thanks!

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Marked as reviewed by fjiang (Committer).

PR Review: https://git.openjdk.org/jdk/pull/23631#pullrequestreview-2621266093