G1 STW phases and FGC column in jstat
kirk at kodewerk.com
kirk at kodewerk.com
Wed Mar 2 10:02:40 UTC 2016
Good question. I’ve never considered CMS to be a Full GC. This implies that there should be separate performance counters for CMS pause phases as it is possible to have FGC. Of course a FGC during CMS maybe user triggered, triggered outside a CMS cycle, interrupts a CMS cycle, or interrupts a CMS phase. I’m not sure how much of a distinction one needs to make here as that could be a quick broader discussion. Certainly the purpose isn’t to recreate the GC logs in these performance counters. But at the very least not having a distinction between full and a STW-CMS phase is kind of misleading in my opinion.
> On Mar 1, 2016, at 5:03 PM, Yasumasa Suenaga <yasuenag at gmail.com> wrote:
> Hi Kirk,
>> It is also incorrect to count initial mark and remark in CMS as a FGC.
> Though, how can we check execution of major collection without GC log?
> Should we add new PerfCounter for CGC (and add CGC column to jstat output)?
> On 2016/03/02 6:35, kirk at kodewerk.com wrote:
>> I think it is incorrect to count remark and cleanup as FGC. They are not full collections. It is also incorrect to count initial mark and remark in CMS as a FGC. It is unfortunate that this is counted this way.
>>> On Mar 1, 2016, at 8:56 AM, Yasumasa Suenaga <yasuenag at gmail.com> wrote:
>>> Hi all,
>>> I wonder that STW phases (Remark and Cleanup) at G1 are not counted in jstat FGC column.
>>> For example, Initial Mark and Remark at CMS are counted as FGC.
>>> For consistency, I think that G1 STW phases should be counted as FGC.
>>> What do you think about it?
>>> If it is accepted, I will file it to JBS and will upload webrev.
>>> suggested fix:
>>> diff -r 8a103ba9a7b2 src/share/vm/gc/g1/g1MonitoringSupport.cpp
>>> --- a/src/share/vm/gc/g1/g1MonitoringSupport.cpp Mon Feb 29 22:54:24 2016 +0900
>>> +++ b/src/share/vm/gc/g1/g1MonitoringSupport.cpp Tue Mar 01 23:43:30 2016 +0900
>>> @@ -103,7 +103,7 @@
>>> // name "collector.1". In a generational collector this would be the
>>> // old generation collection.
>>> _full_collection_counters =
>>> - new CollectorCounters("G1 stop-the-world full collections", 1);
>>> + new CollectorCounters("G1 stop-the-world phase", 1);
>>> // timer sampling for all counters supporting sampling only update the
>>> // used value. See the take_sample() method. G1 requires both used and
>>> diff -r 8a103ba9a7b2 src/share/vm/gc/g1/vm_operations_g1.cpp
>>> --- a/src/share/vm/gc/g1/vm_operations_g1.cpp Mon Feb 29 22:54:24 2016 +0900
>>> +++ b/src/share/vm/gc/g1/vm_operations_g1.cpp Tue Mar 01 23:43:30 2016 +0900
>>> @@ -230,6 +230,8 @@
>>> G1CollectedHeap* g1h = G1CollectedHeap::heap();
>>> GCTraceTime(Info, gc) t(_printGCMessage, g1h->gc_timer_cm(), GCCause::_no_gc, true);
>>> IsGCActiveMark x;
>>> + SvcGCMarker sgcm(SvcGCMarker::OTHER);
>>> + TraceCollectorStats tcs(g1h->g1mm()->full_collection_counters());
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