RFR: 8268231: Aarch64: Use ldp in intrinsics for String.compareTo [v5]

[Wu Yan]

On Wed, 4 Aug 2021 03:29:40 GMT, Nick Gasson <ngasson at openjdk.org> wrote:

> Please provide the updated benchmark results for this version. Are you able to test it on several different machines?

We tested this version on Raspberry Pi 4B.

base:
Benchmark                                     (diff_pos)  (size)  Mode  Cnt    Score    Error  Units
StringCompare.compareLLDiffStrings                     7     256  avgt    5   14.882 ?  0.157  us/op
StringCompare.compareLLDiffStrings                    15     256  avgt    5   15.514 ?  0.094  us/op
StringCompare.compareLLDiffStrings                    31     256  avgt    5   16.756 ?  0.050  us/op
StringCompare.compareLLDiffStrings                    47     256  avgt    5   18.196 ?  0.727  us/op
StringCompare.compareLLDiffStrings                    63     256  avgt    5   20.110 ?  0.075  us/op
StringCompare.compareLLDiffStrings                   127     256  avgt    5   31.458 ?  0.032  us/op
StringCompare.compareLLDiffStrings                   255     256  avgt    5   53.099 ?  1.212  us/op
StringCompare.compareUUDiffStrings                     7     256  avgt    5   15.419 ?  0.012  us/op
StringCompare.compareUUDiffStrings                    15     256  avgt    5   16.761 ?  0.078  us/op
StringCompare.compareUUDiffStrings                    31     256  avgt    5   20.132 ?  0.112  us/op
StringCompare.compareUUDiffStrings                    47     256  avgt    5   27.492 ?  0.104  us/op
StringCompare.compareUUDiffStrings                    63     256  avgt    5   32.147 ?  0.028  us/op
StringCompare.compareUUDiffStrings                   127     256  avgt    5   56.208 ?  0.016  us/op
StringCompare.compareUUDiffStrings                   255     256  avgt    5  100.439 ?  0.782  us/op
StringCompare.compareUUDiffStringsTurnOffCCP           7     256  avgt    5   15.441 ?  0.071  us/op
StringCompare.compareUUDiffStringsTurnOffCCP          15     256  avgt    5   16.781 ?  0.192  us/op
StringCompare.compareUUDiffStringsTurnOffCCP          31     256  avgt    5   20.109 ?  0.010  us/op
StringCompare.compareUUDiffStringsTurnOffCCP          47     256  avgt    5   27.463 ?  0.068  us/op
StringCompare.compareUUDiffStringsTurnOffCCP          63     256  avgt    5   32.168 ?  0.064  us/op
StringCompare.compareUUDiffStringsTurnOffCCP         127     256  avgt    5   56.283 ?  0.551  us/op
StringCompare.compareUUDiffStringsTurnOffCCP         255     256  avgt    5  100.419 ?  0.914  us/op

opt:
Benchmark                                     (diff_pos)  (size)  Mode  Cnt    Score   Error  Units
StringCompare.compareLLDiffStrings                     7     256  avgt    5   14.064 ? 0.048  us/op
StringCompare.compareLLDiffStrings                    15     256  avgt    5   16.079 ? 0.041  us/op
StringCompare.compareLLDiffStrings                    31     256  avgt    5   17.413 ? 0.033  us/op
StringCompare.compareLLDiffStrings                    47     256  avgt    5   18.750 ? 0.012  us/op
StringCompare.compareLLDiffStrings                    63     256  avgt    5   20.093 ? 0.052  us/op
StringCompare.compareLLDiffStrings                   127     256  avgt    5   27.432 ? 0.009  us/op
StringCompare.compareLLDiffStrings                   255     256  avgt    5   44.832 ? 0.173  us/op
StringCompare.compareUUDiffStrings                     7     256  avgt    5   16.071 ? 0.028  us/op
StringCompare.compareUUDiffStrings                    15     256  avgt    5   18.082 ? 0.015  us/op
StringCompare.compareUUDiffStrings                    31     256  avgt    5   20.753 ? 0.006  us/op
StringCompare.compareUUDiffStrings                    47     256  avgt    5   25.427 ? 0.051  us/op
StringCompare.compareUUDiffStrings                    63     256  avgt    5   28.170 ? 0.091  us/op
StringCompare.compareUUDiffStrings                   127     256  avgt    5   42.809 ? 0.143  us/op
StringCompare.compareUUDiffStrings                   255     256  avgt    5   75.056 ? 0.741  us/op
StringCompare.compareUUDiffStringsTurnOffCCP           7     256  avgt    5   16.132 ? 0.195  us/op
StringCompare.compareUUDiffStringsTurnOffCCP          15     256  avgt    5   17.423 ? 0.023  us/op
StringCompare.compareUUDiffStringsTurnOffCCP          31     256  avgt    5   20.102 ? 0.112  us/op
StringCompare.compareUUDiffStringsTurnOffCCP          47     256  avgt    5   25.529 ? 0.367  us/op
StringCompare.compareUUDiffStringsTurnOffCCP          63     256  avgt    5   26.804 ? 0.051  us/op
StringCompare.compareUUDiffStringsTurnOffCCP         127     256  avgt    5   40.988 ? 0.425  us/op
StringCompare.compareUUDiffStringsTurnOffCCP         255     256  avgt    5   77.157 ? 0.187  us/op


On the Raspberry Pi, the improvement is more obvious when the diff_pos is above 127.



> I meant the earlier String.compareTo that this is partially replacing. This one might be fine but I just wanted to check it had be thoroughly tested. For reference they were:
> 
> https://bugs.openjdk.java.net/browse/JDK-8215100
> https://bugs.openjdk.java.net/browse/JDK-8237524
> https://bugs.openjdk.java.net/browse/JDK-8218966

Thank you for your reminder. This version can pass these three test cases. In addition, we tested tier1-tier3 and no new test cases fail.

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PR: https://git.openjdk.java.net/jdk/pull/4722