RFR: Changes to simplify MU accounting

[Kelvin Nilsen]

On Thu, 11 May 2023 21:50:11 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> This represents a small part of the expand-old-on-demand branch.  By itself, this may result in some performance regression because we no longer use MU (mutator utilization) reports to guide generation sizing decisions.  On the other hand, the guidance provided by MU metrics does not seem to be a very accurate predictor of ideal generation sizes.
>
> src/hotspot/share/gc/shenandoah/shenandoahControlThread.cpp line 511:
> 
>> 509:         if (heap->collection_set()->has_old_regions()) {
>> 510:           bool mixed_is_done = (heap->old_heuristics()->unprocessed_old_collection_candidates() == 0);
>> 511:           mmu_tracker->record_mixed(the_generation, GCId::current(), mixed_is_done);
> 
> Could use `ShenandoahControlThread::get_gc_id` or just access `_gc_id` directly. `GCId::current` has thread local access overhead.

Thanks for this.  Replaced in expand-old-on-demand.

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PR Review Comment: https://git.openjdk.org/shenandoah/pull/274#discussion_r1202935031