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<body class='hmmessage'><div dir='ltr'>Hi,<div><br></div><div>I was analyzing the application minor GC pause time with CMS collector on JDK7u25 and JDK6u30.</div><div><br></div><div>I used the hardware with 24 Core, 64 GB, linux.</div><div><br></div><div>JVM settings of my application</div><div><br></div><div>-Xloggc:GC.log -server -XX:+PrintGCDetails -XX:+PrintGCDateStamps -Xms10g -Xmx10g -XX:ReservedCodeCacheSize=512m -XX:CompileThreshold=50 -XX:MaxNewSize=5g -XX:NewSize=5g -XX:PermSize=128m -XX:MaxPermSize=128m -Dcom.sun.management.jmxremote.port=9100 -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false -XX:+UseConcMarkSweepGC -XX:-UseBiasedLocking -XX:-UseCounterDecay</div><div><br></div><div>JDK7 has the extra setting of <span style="font-size: 12pt;"> </span><span style="font-size: 12pt;">-XX:+UnlockDiagnosticVMOptions -XX:ParGCCardsPerStrideChunk=4096</span></div><div><br></div><div>Observation:</div><div> - Without setting -XX:ParralelGCThreads setting, JDK7 minor GC pause time was ~17 msec as compared to ~8-9 msec with JDK6</div><div>-With -XX:ParallelGCThreads upto 10, JDK7 minor GC pause time was lesser than JDK6. But if we increase the ParallelGCThreads count, I have not observed any improvement in JDK7 however there is significant improvement in JDK6 minor GC pause time.</div><div>- With JDK7, <span style="font-size: 12pt;"> </span><span style="font-size: 12pt;">-XX:+UnlockDiagnosticVMOptions -XX:ParGCCardsPerStrideChunk=4096 flags gave me the higher minor GC pause time on</span><span style="font-size: 12pt;"> increasing ParallelGCThreads more than 10.</span></div><div><br></div><div>I have repeated the test, multiple times and observing the same behavior.</div><div><br></div><div>I was wondering why it could be. Can you please share some thought on this?</div><div><br></div><div>Thanks and Regards</div><div>-Niin</div> </div></body>
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