RFR: 8280917: Simplify G1ConcurrentRefineThread activation [v2]

[Kim Barrett]

On Wed, 2 Feb 2022 00:22:50 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> Kim Barrett has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   update copyrights
>
> src/hotspot/share/gc/g1/g1ConcurrentRefineThread.cpp line 188:
> 
>> 186:     // rarely (if ever) dirty cards, so defer activation to a post-safepoint
>> 187:     // notification.
>> 188:     if (SafepointSynchronize::is_at_safepoint()) {
> 
> @walulyai noticed that this test was backward.  Difference in testing is often surprisingly subtle, I suspect because there's enough other wonkiness in the refinement thread control to often mask the effect.  This change as a whole is intended as a step toward fixing that.  I'm sure glad Ivan spotted this now though.

I re-ran tests and ran some additional with this mistake fixed.  No problems encountered.  I also did some better performance testing.  specjbb2015 with options that will trigger the need for more concurrent refinement was unchanged between baseline and with the above fixed.  Having the test backward produced a 6-7% regression.  Thanks again Ivan.

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PR: https://git.openjdk.java.net/jdk/pull/7282