RFR: 8350314: Shenandoah: Capture thread state sync times in GC timings [v6]
Aleksey Shipilev
shade at openjdk.org
Wed Feb 26 19:44:55 UTC 2025
On Wed, 26 Feb 2025 08:12:31 GMT, Xiaolong Peng <xpeng at openjdk.org> wrote:
>> The change is to improve the observability of Shenandoah GC, basically there are three changes for Shenandoah GC timings in this PR:
>>
>> 1. Net GC pause timings include the time to propagate GC state to Java threads
>> 2. Add new timing "Propagate GC state" in Shenandoah GC timing logs
>> 3. Removal of the call of `propagate_gc_state_to_all_threads` from "init_update_refs", which handles gc state in handshake already.
>>
>> With the change, the new GC timing log will be like:
>>
>> [11.056s][info][gc,stats ] Concurrent Reset 89 us
>> [11.056s][info][gc,stats ] Pause Init Mark (G) 257 us
>> [11.056s][info][gc,stats ] Pause Init Mark (N) 17 us
>> [11.056s][info][gc,stats ] Update Region States 3 us
>> [11.056s][info][gc,stats ] Propagate GC state 1 us
>> [11.056s][info][gc,stats ] Concurrent Mark Roots 232 us, parallelism: 1.96x
>> [11.056s][info][gc,stats ] CMR: <total> 456 us
>> [11.056s][info][gc,stats ] CMR: Thread Roots 429 us, workers (us): 139, 148, 142, ---, ---, ---,
>> [11.057s][info][gc,stats ] CMR: VM Strong Roots 11 us, workers (us): 8, 3, 0, ---, ---, ---,
>> [11.057s][info][gc,stats ] CMR: CLDG Roots 16 us, workers (us): 16, ---, ---, ---, ---, ---,
>> [11.057s][info][gc,stats ] Concurrent Marking 1304 us, parallelism: 2.33x
>> [11.057s][info][gc,stats ] CM: <total> 3043 us
>> [11.057s][info][gc,stats ] CM: Parallel Mark 3043 us, workers (us): 1023, 1017, 1003, ---, ---, ---,
>> [11.057s][info][gc,stats ] Flush SATB 204 us
>> [11.057s][info][gc,stats ] Pause Final Mark (G) 865 us
>> [11.057s][info][gc,stats ] Pause Final Mark (N) 234 us
>> [11.057s][info][gc,stats ] Finish Mark 129 us, parallelism: 0.01x
>> [11.057s][info][gc,stats ] Propagate GC state 2 us
>> [11.057s][info][gc,stats ] Update Region States 12 us
>> [11.057s][info][gc,stats ] Choose Collection Set 25 us
>> [11.057s][info][gc,stats ] Rebuild Free Set 29 us
>> [11.057s][info][gc,stats ] Concurrent Weak References 67 us, parallelism: 0.25x
>> [11.057s][info][gc,stats ] CWRF: <total> 17 us
>> [11.057s][info][gc,...
>
> Xiaolong Peng has updated the pull request incrementally with one additional commit since the last revision:
>
> Remove trailing whitespace
src/hotspot/share/gc/shenandoah/shenandoahConcurrentGC.cpp line 693:
> 691:
> 692: {
> 693: ShenandoahGCPhase phase(ShenandoahPhaseTimings::init_propagate_gc_state);
Here and later, I messed up my suggestion. I think these should be `ShenandoahTimingsTracker`, not `ShenandoahGCPhase`. `ShenandoahGCPhase` does more stuff we don't need. `ShenandoahTimingsTracker` does only the basic stuff.
src/hotspot/share/gc/shenandoah/shenandoahDegeneratedGC.cpp line 86:
> 84: op_degenerated();
> 85: heap->set_degenerated_gc_in_progress(false);
> 86: {
A bit sad we need to do this due to `op_degenerated` early returns, but fine.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/23759#discussion_r1972273776
PR Review Comment: https://git.openjdk.org/jdk/pull/23759#discussion_r1972269107
More information about the hotspot-gc-dev
mailing list