RFR: 8361376: Regressions 1-6% in several Renaissance in 26-b4 only MacOSX aarch64 [v5]

[Kim Barrett]

On Tue, 5 Aug 2025 10:13:03 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> Dean Long has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   one unconditional release should be enough
>
> Thanks for implementing nice code for PPC64! I appreciate it! The shared code and the other platforms look fine, too.
> Maybe atomic bitwise operations could be used, but I'm happy with your current solution.

> Thanks @TheRealMDoerr . I didn't even consider atomic bitwise operations, but that's a good idea. I'm not in a hurry to push this, so if you could provide an atomic bitwise patch for ppc64, I would be happy to include it. In the mean time, I'm still investigating the ZGC regression. If I can figure it out, I might want to include a fix for ZGC in this PR as well.

Not a review, just a drive-by comment.
We've had Atomic bitops for a while now.
Atomic::fetch_then_{and,or,xor}(ptr, bits [, order])
Atomic::{and,or,xor}_then_fetch(ptr, bits [, order])
They haven't been optimized for most (any?) platforms, being based on cmpxchg.
(See all the "Specialize atomic bitset functions for ..." related to
https://bugs.openjdk.org/browse/JDK-8293117.)

-------------

PR Comment: https://git.openjdk.org/jdk/pull/26399#issuecomment-3157237736