Hi, We recently switched our Java application from CMS to G1. Since then we observed increased CPU time (user cpu) and latency for the requests.
*Observations* - Count of GC pauses remains the same with CMS and G1 and so does the pause time. - My initial suspicion was that the application threads were competing with GC threads to get CPU cycles. But I don't see any indication of increased concurrent time in GC logs. I suspect that the overhead associated with read/write barriers could be the reason for the increased CPU cycles but I want to confirm that. *Are there any GC flags that prints statistics about read/write barriers? Or is there a way to debug this?* java -version openjdk version "1.8.0_222" OpenJDK Runtime Environment Corretto-8.222.10.1 (build 1.8.0_222-b10) OpenJDK 64-Bit Server VM Corretto-8.222.10.1 (build 25.222-b10, mixed mode) These are the command line flags I find in GC logs that the application uses. -XX:+UseG1GC -XX:CICompilerCount=3 -XX:CompressedClassSpaceSize=931135488 -XX:ConcGCThreads=1 -XX:G1HeapRegionSize=4194304 -XX:InitialCodeCacheSize=402653184 -XX:InitialHeapSize=8589934592 -XX:InitialTenuringThreshold=6 -XX:InitiatingHeapOccupancyPercent=50 -XX:MarkStackSize=4194304 -XX:MaxGCPauseMillis=200 -XX:MaxHeapSize=8589934592 -XX:MaxMetaspaceSize=939524096 -XX:MaxNewSize=5150605312 -XX:MaxTenuringThreshold=6 -XX:MetaspaceSize=268435456 -XX:MinHeapDeltaBytes=4194304 -XX:+ParallelRefProcEnabled -XX:+PrintAdaptiveSizePolicy -XX:+PrintClassHistogram -XX:+PrintGC -XX:+PrintGCApplicationStoppedTime -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintSafepointStatistics -XX:PrintSafepointStatisticsCount=1 -XX:PrintSafepointStatisticsTimeout=1000 -XX:+PrintTenuringDistribution -XX:ReservedCodeCacheSize=402653184 -XX:+ScavengeBeforeFullGC -XX:SoftRefLRUPolicyMSPerMB=2048 -XX:StackShadowPages=20 -XX:ThreadStackSize=512 -XX:+TieredCompilation -XX:+UseBiasedLocking -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseFastAccessorMethods -XX:+UseLargePages -XX:+UseTLAB Let me know if I need to provide any other information. Regards, Prasanth
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