RFR: 8318986: Improve GenericWaitBarrier performance [v3]

[Aleksey Shipilev]

On Tue, 7 Nov 2023 08:51:20 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

>> Aleksey Shipilev has updated the pull request incrementally with four additional commits since the last revision:
>> 
>>  - Touchups
>>  - More comments work
>>  - Tight up the comments
>>  - Rework to a single atomic counter per cell
>
> src/hotspot/share/utilities/waitBarrier_generic.cpp line 120:
> 
>> 118:   SpinYield sp;
>> 119:   while (Atomic::load_acquire(&_state) < -1) {
>> 120:     sp.wait();
> 
> A warning once would be helpful that cells might be too few.

Yes, but I am a bit uncomfortable with printing performance warnings from a generic synchronization primitive. At very least because it might intermittently break some tests that check the outputs. So I'd rather avoid adding stuff here.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16404#discussion_r1384649730