JDK7 Minor GC pause as compared to JDK6

[Nitin Jalan]

Hi,
I was analyzing the application minor GC pause time with CMS collector on JDK7u25 and JDK6u30.
I used the hardware with 24 Core, 64 GB, linux.
JVM settings of my application
-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
JDK7 has the extra setting of  -XX:+UnlockDiagnosticVMOptions -XX:ParGCCardsPerStrideChunk=4096
Observation: - Without setting -XX:ParralelGCThreads setting, JDK7 minor GC pause time was ~17 msec as compared to ~8-9 msec with JDK6-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.- With JDK7,  -XX:+UnlockDiagnosticVMOptions -XX:ParGCCardsPerStrideChunk=4096 flags gave me the higher minor GC pause time on increasing ParallelGCThreads more than 10.
I have repeated the test, multiple times and observing the same behavior.
I was wondering why it could be. Can you please share some thought on this?
Thanks and Regards-Niin 		 	   		   		 	   		  
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