RFR: 8261492: Shenandoah: reconsider forwardee accesses memory ordering [v8]

[Aleksey Shipilev]

On Tue, 31 Aug 2021 13:24:37 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Add TODO
>
> More work: leave `acquire`-in-lieu-of-`consume` in, and special case the heap update paths to dodge the performance penalty of doing so. Seems to work on x86_64 and AArch64.

> @shipilev Hi, I have tested this pull request as well as this pull request + `OrderAccess::release();` on specjbb 2015 on AArch64 (Kunpeng 920). Maybe there is a slight improvement on critical-jOPS? Here is the result.

Thanks for testing. So explicit barrier does seem to result in a slight bump in critical-jOPS.

I assume "base" results are this PR? If so, do you have performance results for the current master? In other words, it would be interesting to see three results: baseline (current master), this PR, and this PR + `OrderAccess::release()`.

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PR: https://git.openjdk.java.net/jdk/pull/2496