RFR: 8295476: Split G1 cost per byte predictor on gc phase

[Thomas Schatzl]

On Mon, 31 Oct 2022 15:15:27 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Hi,
>> 
>>   please review this change to the cost-per-byte predictor to be split on gc phase (young-only/mixed) instead of during marking/outside of marking.
>> 
>> The reason is that the distinction between young-only/mixed of these values is higher than marking/outside of marking, although the latter degrades somewhat to the former in case of continuous concurrent marking where both are almost equivalent anyway. I believe that has been the original reason to do the marking/not-marking distinction.
>> 
>> I also removed the implied 10% extra cost for copies during marking (i.e. during the young-only phase). I could not find any particular reason why copying would be more expensive then with the current code base.
>> 
>> The distinction in general makes sense as the data copied during young-only and mixed is different (only short-lived data vs. short+long-lived data).
>> 
>> Testing: gha, examining predictions with some benchmarks
>> 
>> Thanks,
>>   Thomas
>
> Marked as reviewed by ayang (Reviewer).

Thanks @albertnetymk @walulyai @kimbarrett for your reviews

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PR: https://git.openjdk.org/jdk/pull/10862