RFR: 8320318: ObjectMonitor Responsible thread

[Martin Doerr]

On Thu, 12 Sep 2024 12:27:44 GMT, Fredrik Bredberg <fbredberg at openjdk.org> wrote:

>> I've run it through our nightly testing (x86_64, aarch64, PPC64 with several OSes) and the good news is that I haven't seen any functional problems. Performance looks also good for the SPEC benchmarks. I don't think they stress Java monitors very strongly.
>> 
>> I've rerun the `LockUnlock` micro benchmark with this patch applied, but `LockUnlock.java` reverted to the original version. This makes `LockUnlock.testContendedLock` faster, but not as fast as without this patch (on the 96 Thread Xeon linux server, similar on Power10). Would be great if anybody could confirm.
>> I think this should at least be documented and the description of the JBS issue improved.
>
> @TheRealMDoerr 
>> I've run it through our nightly testing (x86_64, aarch64, PPC64 with several OSes) and the good news is that I haven't seen any functional problems. Performance looks also good for the SPEC benchmarks. I don't think they stress Java monitors very strongly.
> 
> That really is good news! Thanks for testing!
> 
>> I've rerun the `LockUnlock` micro benchmark with this patch applied, but `LockUnlock.java` reverted to the original version. This makes `LockUnlock.testContendedLock` faster, but not as fast as without this patch (on the 96 Thread Xeon linux server, similar on Power10). Would be great if anybody could confirm. I think this should at least be documented and the description of the JBS issue improved.
> 
> Tanks for confirming that my suspension was right. As I stated earlier, due to the added StoreLoad barrier a slight decrease in performance is probably to be expected if you just run `LockUnlock.testContendedLock`, but it shouldn't really matter when running real life applications. Anyhow I'll update the description of the JBS issue.

@fbredber: If you need help to resolve the PPC64 conflicts with https://github.com/openjdk/jdk/commit/7579d3740217e4a819cbf63837ec929f00464585, just let me know.

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PR Comment: https://git.openjdk.org/jdk/pull/19454#issuecomment-2363155597