RFR: 8322484: 22-b26 Regression in J2dBench-bimg_misc-G1 (and more) on Windows-x64 and macOS-x64

[Thomas Schatzl]

On Wed, 24 Jan 2024 12:38:09 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

> Hi all,
> 
>   please review this improvement to managing region pin counts in g1.
> 
> Some applications do millions of `Get/ReleasePrimitiveArrayCritical` operations per second, in particular some of the j2dbench benchmarks (e.g. vimg_copyarea 10M/s), on some platforms. Every pin/unpin results in an atomic operation that is the cause for these slowdown. 
> 
> Only Windows seems to be significantly affected.
> 
> This suggested change implements a per-region thread local cache storing the current pin/unpin refcount difference, writing it back only when a thread pins/unpin an object in a different region.
> 
> For these benchmarks this often reduces the amount of atomic operations to none, or a few handful; the worst improvement I have seen is that effective atomic operations were reduced to 1/10th. Overall all the j2dbench benchmark scores improve.
> 
> There is a remaining issue with the `vimg_shapes_gradient` J2dbench subbenchmark: comparing the original results (before integration of region pinning) with latest jdk23 results, there is a regression of about 5%; this is caused by the backout of a bad compiler change (https://bugs.openjdk.org/browse/JDK-8322985). This will be fixed by its redo CR https://bugs.openjdk.org/browse/JDK-8323116.
> 
> Testing: tier1-3, j2dbench, dacapo, specj*, renaissance benchmarks
> 
> Thanks,
>   Thomas

The [e1bb807](https://github.com/openjdk/jdk/pull/17552/commits/e1bb807f65b517f89c1ef7442f79ab121a3c3f82) change passed tier1-7. (The removal of the assert in https://github.com/openjdk/jdk/pull/17552/commits/4991abb28623d4484d4a30e2af0ed2afbb5d3942 won't invalidate that)

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PR Comment: https://git.openjdk.org/jdk/pull/17552#issuecomment-1911736475