RFR: 8264846: Regression ~5% in J2dBench.bimg_misc on Linux after JDK-8263142

[Erik Joelsson]

On Wed, 12 May 2021 00:06:34 GMT, Sergey Bylokhov <serb at openjdk.org> wrote:

> Performance in one of the tests in the bimg_misc group is dropped by 20%(or 5% of the group) after some unused code was removed from the libawt. I assume the size of the lib became smaller and GCC heuristics were changed to do not try to increase the size by inlining over some percent. I tested various options but most of them affect different test cases in the opposite ways.
> 
> While testing I have found that the most profitable option is to simply use the "O3" optimization level, moreover, after offline discussion, we have found that this optimization level was used before, but due to the typo, we missed this option and fallback to the "LOW" level.
> 
> Note this will change optimization level for all platforms in case of any regressions we may try to implement this change for GGC only or we may try to use just these options to solve this performance issue: " -ftree-loop-vectorize -fversion-loops-for-strides "
> 
> 
> Summary:
>   b12:
>     Number of tests: 13
>     Overall average: 1222067.1646119351
>     Best spread: 0.07% variance
>     Worst spread: 3.22% variance
>     (Basis for results comparison)
> 
>   o3:
>     Number of tests: 13
>     Overall average: 1991716.540920269
>     Best spread: 0.0% variance
>     Worst spread: 2.22% variance
>     Comparison to basis:
>       Best result: 314.15% of basis
>       Worst result: 97.23% of basis
>       Number of wins: 8
>       Number of ties: 4
>       Number of losses: 1
> 
>   two options:
>     Number of tests: 13
>     Overall average: 1971528.6542701898
>     Best spread: 0.0% variance
>     Worst spread: 7.08% variance
>     Comparison to basis:
>       Best result: 312.05% of basis
>       Worst result: 77.27% of basis
>       Number of wins: 6
>       Number of ties: 1
>       Number of losses: 6

Marked as reviewed by erikj (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/3990