G1 STW phases and FGC column in jstat (original) (raw)

Yasumasa Suenaga yasuenag at gmail.com
Wed Mar 2 12:58:29 UTC 2016

Hi Kirk,

Agree to you. However, I use occasional FGC counter at CMS as below:

  1. Check major collection occurrence Some production systems have large memory as Java heap, and they are not set GC log. If their CPU usage becomes high, I want to check GC execution. (Of course, we have to check any other points :-) )

  2. Core image analysis If JVM is crashed, I want to check PerfCounter to know situation. (In the past, I sometimes encountered crash at GC worker thread.)

I guess that I will want to check them at G1.

Thus, at least, I want to add PerfCounter for CGC (and add JVMTI event hook). However, this proposal will affect to jstat spec. So I want to discuss about it before filing to JBS.

Thanks,

Yasumasa

On 2016/03/02 19:02, kirk at kodewerk.com wrote:

Hi Yasumasa,

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. Regards, Kirk

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)?

Yasumasa On 2016/03/02 6:35, kirk at kodewerk.com wrote: Hi, 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. Regards, Kirk

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. fullcollectioncounters = - 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 takesample() method. G1 requires both used and diff -r 8a103ba9a7b2 src/share/vm/gc/g1/vmoperationsg1.cpp --- a/src/share/vm/gc/g1/vmoperationsg1.cpp Mon Feb 29 22:54:24 2016 +0900 +++ b/src/share/vm/gc/g1/vmoperationsg1.cpp Tue Mar 01 23:43:30 2016 +0900 @@ -230,6 +230,8 @@ G1CollectedHeap* g1h = G1CollectedHeap::heap(); GCTraceTime(Info, gc) t(printGCMessage, g1h->gctimercm(), GCCause::nogc, true); IsGCActiveMark x; + SvcGCMarker sgcm(SvcGCMarker::OTHER); + TraceCollectorStats tcs(g1h->g1mm()->fullcollectioncounters()); cl->dovoid(); } ---------------------- Thanks, Yasumasa

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