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, k...@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 <yasue...@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, k...@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 <yasue...@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());
_cl->do_void();
}
----------------------
Thanks,
Yasumasa
