High CPU in JVM compiler threads

Solution Verified - Updated

Environment

  • JBoss Enterprise Application Platform (EAP)
  • Java

Issue

  • We see high CPU in our JVM compiler threads

Resolution

  • Limit compiler usage by limiting the compiler thread count and increasing the compiler threshold:
-XX:CICompilerCount=1 -XX:CompileThreshold=20000 -XX:Tier3CompileThreshold=5000 -XX:Tier4CompileThreshold=30000

in the later versions of Java, TieredCompilation is default to true, CICompilerCount will needs to be greater than 1 otherwise JVM will not start, i.e

-XX:CICompilerCount=2 -XX:CompileThreshold=20000 -XX:Tier3CompileThreshold=5000 -XX:Tier4CompileThreshold=30000
  • Increase the size of the code cache to avoid exhaustion. It defaults to 240 mb for java 8. Note this is an additional reserved space outside the heap/meta:
-XX:InitialCodeCacheSize=512m -XX:ReservedCodeCacheSize=512m

Root Cause

  • The code cache may be exhausted, causing frequent flushing and recompiling of frequently used methods

Diagnostic Steps

  • Add -XX:+PrintCompilation to your JVM options for further details on compiler activity. Redirect console output to a file to capture this data.
  • See Solving OpenJDK C2 compilation issues for logging format details, and for PrintCompilation log interpretation.
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