RFR: 8193559: ugly DO_JAVA_THREADS macro should be replaced [v4]

[Kim Barrett]

On Sat, 31 Jul 2021 14:37:29 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> I agree that it should be okay without prefetch. I added it when I was running on a 4096 strand SPARC machine running over 8000 threads, and walking the list would approach 1 ms. While intuitively linear scan should be good enough, I did actually measure slight improvements with explicit prefetching, and the slight improvements did seem worth it at the time as the amount of time spent in there was non-trivial.
>> Now we don't support that kind of hardware any longer, so I don't think this trick would necessarily spark as much joy any longer.
>> I don't mind if we do or do not perform the prefetching. I'm okay either way.
>
> I'm going to leave resolution of the prefetch question to a follow-up bug.
> I think that discussion deserves a separate issue.

OK.

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PR: https://git.openjdk.java.net/jdk/pull/4671