[perf] System.Runtime.Intrinsics.** performance regressions in Mono AOT x64 microbenchmarks from Preview 5 to Preview 7

[kotlarmilos]

Description

The following performance regressions occurred between the Preview 5 snapshot (May 2nd, 2023) and Preview 7 snapshot (July 19th, 2023).

The configuration used for the benchmarks is Mono AOT with LLVM on x64 ubuntu 18.04.

Name	Baseline Value	Compare Value	% Difference
System.Runtime.Intrinsics.Tests.Perf_Vector128Of<UInt64>.DivideBenchmark	18.89	20.22	7.04
System.Runtime.Intrinsics.Tests.Perf_Vector128Of<SByte>.GetHashCodeBenchmark	98.32	105.83	7.64

[kotlarmilos]

@vargaz @fanyang-mono There are a number of Vector128 improvements in #89238 and I assume we can close this issue.

[fanyang-mono]

I don't understand your last comment. I searched in #89238. And these two microbenchmarks also showed as regressions. How that could help close this issue?

[kotlarmilos]

There are a lot of Vector128 improvements and a few regressions. Sometimes, the regressions are considered as a tradeoff where general cases improved but edge cases regressed. Not sure if it is the case here, but if not, we should mitigate it.

[fanyang-mono]

There are two things here:

1. These Vector128 microbenchmarks are quite independent from each other. Even though most of them got improved, the regressed ones still worth looking into.
2. Like I mentioned in [perf] System.Numerics.** performance regressions in Mono AOT x64 microbenchmarks from Preview 5 to Preview 7 #89246, we should collect results with average of a couple data points. These looks like false positive to me. The performance of these two microbenchmarks didn't change.

[kotlarmilos]

Thanks for the info. Here are the last 10 runs with the baseline before the regression, and the targets after the recovery.

System.Runtime.Intrinsics.Tests.Perf_Vector128Of.DivideBenchmark

Run	Baseline	Target
1	18,78173253	18,79884798
2	18,76230461	18,62760552
3	18,76230461	18,69527468
4	18,79260984	19,9226462
5	19,01008983	18,65647022
6	19,12448913	18,83510237
7	18,85043033	20,09960835
8	18,7581046	20,14199486
9	18,73615193	20,15739381
10	18,74319966	20,15808063
avg	18,83214171	19,40930246

System.Runtime.Intrinsics.Tests.Perf_Vector128Of.GetHashCodeBenchmark

Run	Baseline	Target
1	97,80791568	105,8302407
2	97,87356477	103,1638385
3	98,30399123	104,7245511
4	98,89306389	104,3972979
5	98,09571083	96,46227839
6	97,78725048	104,6662993
7	97,79220034	103,1119935
8	102,149487	104,1949933
9	102,0973694	104,143184
10	102,3439054	104,327521
avg	99,3144459	103,5022198

In both cases it looks like noise, thus closing this issues.