RFR: 8337511: Implement JEP 404: Generational Shenandoah (Experimental) [v3]

[Y. Srinivas Ramakrishna]

On Tue, 22 Oct 2024 17:12:38 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

>> Congratulations! Good to see the great progress. I just built this PR for some testing and found something unexpected. I ran the genshen VS shenandoah(default) with jbb2015 on aarch64 N2 with 8 cores and Xmx8g. The critical-jOPS of genshen(5373) is behind shenandoah(6027). Do I miss something on the options?
>> ```java -Xmx8g -XX:+UseShenandoahGC -XX:+UnlockExperimentalVMOptions -XX:ShenandoahGCHeuristics=adaptive -XX:ShenandoahGCMode=generational -Xlog:gc*  -XX:MetaspaceSize=1g   -jar specjbb2015.jar -m COMPOSITE```
>
>> @mmyxym , Thank you for testing this out! I apologize for not responding to your comment sooner. We run specjbb2015 regularly in our integration pipeline. We see a slight improvement with the generational mode; certainly no regression:
>> 
>> ```
>> Shen: RUN RESULT: hbIR (max attempted) = 4701, hbIR (settled) = 3934, max-jOPS = 3620, critical-jOPS = 2375
>> Gen:  RUN RESULT: hbIR (max attempted) = 3934, hbIR (settled) = 3295, max-jOPS = 4013, critical-jOPS = 2470
>> Shen: RUN RESULT: hbIR (max attempted) = 4701, hbIR (settled) = 3934, max-jOPS = 3667, critical-jOPS = 2397
>> Gen:  RUN RESULT: hbIR (max attempted) = 4701, hbIR (settled) = 3934, max-jOPS = 3996, critical-jOPS = 2414
>> ```
>> 
>> These results were produced with these arguments:
>> 
>> ```
>> -XX:+UseShenandoahGC -XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticV
>> MOptions -XX:-TieredCompilation -XX:-ShenandoahPacing -XX:+AlwaysPreTouch -XX:+DisableExplicitGC -Xmx10g -Xms10g -XX:ShenandoahGCMode=generational
>> ```
>> 
>> These runs executed on a Graviton2 host with 4 cores, 16G. I'll run again on a host with more cores and with your exact command line parameters.
> 
> What's the reason to disable tiered compilation?

@zhengyu123 and @shipilev : could you please take another look and leave your review feedback and/or approval? We'd like to land the changes this week if possible. Currently internal testing is in progress after merging with the latest changes from tip. Thanks!

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

PR Comment: https://git.openjdk.org/jdk/pull/21273#issuecomment-2469466977