Bug in G1 logging? incorrect stop times?

Thomas Viessmann thomas.viessmann at oracle.com
Fri Aug 29 12:15:18 UTC 2014


Hi all,


I suspect a bug in G1 logging. Before I file a (possibly incorrect) bug 
I would like to ask here.
Is my understanding correct that the stw evacuation phase starts at 
*48448.931* and ends at *48454**.034* ?
This would mean a stop time of 5.103 s, which is clearly a mismatch to 
the reported *9.3426141* s
If the stw phase in fact started at a later time e.g. at *48449.288 
*then the stop pause would have been even shorter.

In addition I do not understand how all the relatively short evacuation 
phases sum up to several seconds.
If I add all the MAX values *69.1 + 22.2 + 45+ 150.8 + 0.1 + 155.1 + 0.9 
+ 0.5**= 443.7**ms*




48443.380: Total time for which application threads were stopped: 
0.0084701 seconds
*48448.931*: [GC pause (mixed) 48448.931: [G1Ergonomics (CSet 
Construction) start choosing CSet, _pending_cards: 89458, predicted base 
time: 73.58 ms, remaining time: 176.42 ms, target pause time: 250.00 ms]
  48448.931: [G1Ergonomics (CSet Construction) add young regions to 
CSet, eden: 33 regions, survivors: 5 regions, predicted young region 
time: 35.73 ms]
  48448.933: [G1Ergonomics (CSet Construction) finish adding old regions 
to CSet, reason: reclaimable percentage not over threshold, old: 19 
regions, max: 77 regions, reclaimable: 2570649712 bytes (9.98 %), 
threshold: 10.00 %]
  48448.933: [G1Ergonomics (CSet Construction) added expensive regions 
to CSet, reason: old CSet region num not reached min, old: 19 regions, 
expensive: 7 regions, min: 26 regions, remaining time: 0.00 ms]
  48448.933: [G1Ergonomics (CSet Construction) finish choosing CSet, 
eden: 33 regions, survivors: 5 regions, old: 19 regions, predicted pause 
time: 340.58 ms, target pause time: 250.00 ms]
48449.252: [SoftReference, 962 refs, 0.0064679 secs]48449.259: 
[WeakReference, 7411 refs, 0.0027722 secs]48449.261: [FinalReference, 
272 refs, 0.0022754 secs]48449.264: [PhantomReference, 6 refs, 0.0024348 
secs]48449.266: [JNI Weak Reference, 0.0000337 secs] 48449.288: 
[G1Ergonomics (Concurrent Cycles) do not request concurrent cycle 
initiation, reason: still doing mixed collections, occupancy: 
14898167808 bytes, allocation request: 0 bytes, threshold: 11596411665 
bytes (45.00 %), source: end of GC]
*48449.288*: [G1Ergonomics (Mixed GCs) do not continue mixed GCs, 
reason: reclaimable percentage not over threshold, candidate old 
regions: 156 regions, reclaimable: 2570649712 bytes (9.98 %), threshold: 
10.00 %]
, 0.3573636 secs]
    [Parallel Time: 314.9 ms, GC Workers: 40]
       [GC Worker Start (ms): Min: 48448933.6, Avg: 48448934.2, Max: 
48448934.7, Diff: 1.1]
       [Ext Root Scanning (ms): Min: 15.1, Avg: 17.7, Max: *69.1*, Diff: 
54.0, Sum: 708.0]
       [Update RS (ms): Min: 0.0, Avg: 14.5, Max: *22.2*, Diff: 22.2, 
Sum: 580.3]
          [Processed Buffers: Min: 0, Avg: 22.0, Max: *45*, Diff: 45, 
Sum: 879]
       [Scan RS (ms): Min: 88.7, Avg: 142.6, Max: *150.8*, Diff: 62.1, 
Sum: 5705.2]
       [Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: *0.1*, Diff: 
0.1, Sum: 0.1]
       [Object Copy (ms): Min: 131.4, Avg: 138.2, Max: *155.1*, Diff: 
23.8, Sum: 5526.6]
       [Termination (ms): Min: 0.0, Avg: 0.7, Max: *0.9*, Diff: 0.9, 
Sum: 27.2]
       [GC Worker Other (ms): Min: 0.0, Avg: 0.3, Max: *0.5*, Diff: 0.5, 
Sum: 10.0]
       [GC Worker Total (ms): Min: 313.2, Avg: 313.9, Max: *314.7*, 
Diff: 1.5, Sum: 12557.5]
       [GC Worker End (ms): Min: 48449247.9, Avg: 48449248.1, Max: 
48449248.4, Diff: 0.5]
    [Code Root Fixup: 2.2 ms]
    [Code Root Migration: 0.2 ms]
    [Clear CT: 2.0 ms]
    [Other: 38.2 ms]
       [Choose CSet: 1.7 ms]
       [Ref Proc: 15.6 ms]
       [Ref Enq: 1.2 ms]
       [Free CSet: 2.4 ms]
    [Eden: 1056.0M(1056.0M)->0.0B(1088.0M) Survivors: 160.0M->128.0M 
Heap: 14.5G(24.0G)->13.9G(24.0G)]
  [Times: user=12.45 sys=0.03, real=0.36 secs]
*48454**.034*: Total time for which application threads were stopped: 
*9.3426141* seconds

For completeness; here are the cmd line options:


/usr/jdk/instances/jdk1.7.0/bin/sparcv9/java -Xms24g -Xmx24g -server  
-XX:StringTableSize=27001  -XX:PermSize=512m -XX:MaxPermSize=512m  -Xss512k
-XX:+UseG1GC  -XX:SoftRefLRUPolicyMSPerMB=500 -XX:+PrintGCDetails 
-XX:+PrintGCTimeStamps -Xloggc:/var/cacao/instances/oem-ec/logs/gc.log 
-XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=10 
-XX:GCLogFileSize=10m  -XX:+PrintGCApplicationStoppedTime 
-XX:MaxGCPauseMillis=250-XX:InitiatingHeapOccupancyPercent=45 
-XX:+ParallelRefProcEnabled  -XX:ParallelGCThreads=40 
-XX:+PrintAdaptiveSizePolicy  -XX:+PrintSafepointStatistics 
-XX:+PrintReferenceGC  -XX:G1HeapRegionSize=32m -XX:HeapBaseMinAddress=2G



Thanks and Regards

Thomas

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