RFR: 8271579: G1: Move copy before CAS in do_copy_to_survivor_space

[Hamlin Li]

On Wed, 4 Aug 2021 01:06:47 GMT, Hamlin Li <mli at openjdk.org> wrote:

> Propose to move copy before CAS in do_copy_to_survivor_space, as we found this will improve G1 performance. Specjbb shows 3.7% in critical on aarch64, no change in max.
> 
> After this change copy_to_survivor in G1 is also aligned with PS's copy_to_survivor.

Not quite sure, it could be related to the pipeline scheduling at CPU level.
BTW, I just uploaded the test result for x86, no regression for x86.

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PR: https://git.openjdk.java.net/jdk/pull/4983