RFR: 8292591: Experimentally add back barrier-less Java thread transitions [v5]

[Erik Österlund]

On Fri, 9 Sep 2022 10:05:11 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

>> Please consider, only implemented on x64/aarch64 linux/windows. (@TheRealMDoerr have now contributed PPC64)
>> 
>> On my box calling clock_gettime via JNI goes from 35ns to 28ns when enabled.
>> 
>> Passes t1-7 with option forced on, also passes t1-4 as is in this PR.
>
> Robbin Ehn has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fixed ws

Marked as reviewed by eosterlund (Reviewer).

This looks good to me. I looked through the code to see if I can find any additional thread state filtering that would now require the system memory barrier to work reliably, but could not find any. So it would seem that you found them all.

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PR: https://git.openjdk.org/jdk/pull/10123