jvm-jit-compilation
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petrbouda
JVM JIT Compilation
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https://www.lmax.com/blog/staff-blogs/2016/03/05/observing-jvm-warm-effects/
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https://www.slideshare.net/dougqh/jvm-mechanics-when-does-the
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https://stackoverflow.com/questions/35601841/how-does-the-jvm-decided-to-jit-compile-a-method-categorize-a-method-as-hot/35614237#35614237
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https://stackoverflow.com/questions/71318011/how-is-the-count-of-method-executions-that-triggers-the-omitted-exception-stack/71375155#71375155 (explains
Tier0BackedgeNotifyFreqLog,Tier3BackedgeNotifyFreqLog- the reason why the invocation/backedge counters are not precise) -
https://stackoverflow.com/questions/60851417/jit-recompiles-to-do-fast-throw-after-more-iterations-if-stacktrace-is-of-even-l/60878577#60878577
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http://hg.openjdk.java.net/jdk8u/jdk8u/hotspot/file/2b2511bd3cc8/src/share/vm/runtime/advancedThresholdPolicy.hpp#l34
Thresholds
java -XX:+UnlockDiagnosticVMOptions -XX:+PrintFlagsFinal -version | grep -e Tier
uintx IncreaseFirstTierCompileThresholdAt = 50 {product} {default}
bool PrintTieredEvents = false {product} {default}
intx Tier0BackedgeNotifyFreqLog = 10 {product} {default}
intx Tier0Delay = 20 {diagnostic} {default}
intx Tier0InvokeNotifyFreqLog = 7 {product} {default}
intx Tier0ProfilingStartPercentage = 200 {product} {default}
intx Tier23InlineeNotifyFreqLog = 20 {product} {default}
intx Tier2BackEdgeThreshold = 0 {product} {default}
intx Tier2BackedgeNotifyFreqLog = 14 {product} {default}
intx Tier2CompileThreshold = 0 {product} {default}
intx Tier2InvokeNotifyFreqLog = 11 {product} {default}
intx Tier3BackEdgeThreshold = 60000 {product} {default}
intx Tier3BackedgeNotifyFreqLog = 13 {product} {default}
intx Tier3CompileThreshold = 2000 {product} {default}
intx Tier3DelayOff = 2 {product} {default}
intx Tier3DelayOn = 5 {product} {default}
intx Tier3InvocationThreshold = 200 {product} {default}
intx Tier3InvokeNotifyFreqLog = 10 {product} {default}
intx Tier3LoadFeedback = 5 {product} {default}
intx Tier3MinInvocationThreshold = 100 {product} {default}
intx Tier4BackEdgeThreshold = 40000 {product} {default}
intx Tier4CompileThreshold = 15000 {product} {default}
intx Tier4InvocationThreshold = 5000 {product} {default}
intx Tier4LoadFeedback = 3 {product} {default}
intx Tier4MinInvocationThreshold = 600 {product} {default}
bool TieredCompilation = true {pd product} {default}
intx TieredCompileTaskTimeout = 50 {product} {default}
intx TieredOldPercentage = 1000 {diagnostic} {default}
intx TieredRateUpdateMaxTime = 25 {product} {default}
intx TieredRateUpdateMinTime = 1 {product} {default}
intx TieredStopAtLevel = 4 {product} {default}
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CompileThreshold does make sense if TieredCompilation is disabled (Server JIT)
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IncreaseFirstTierCompileThresholdAt
Increase the compile threshold for C1 compilation if the code
cache is filled by the specified percentage
- CompileThresholdScaling
Factor to control when first compilation happens
(both with and without tiered compilation):
values greater than 1.0 delay counter overflow,
values between 0 and 1.0 rush counter overflow,
value of 1.0 leaves compilation thresholds unchanged
value of 0.0 is equivalent to -Xint.
Flag can be set as per-method option.
If a value is specified for a method, compilation thresholds
for that method are scaled by both the value of the global flag
and the value of the per-method flag.
Tiered Compilation Phases
Tier3InvocationThreshold
java -XX:+UnlockDiagnosticVMOptions -XX:+PrintFlagsFinal -version | grep Tier3InvocationThreshold
intx Tier3InvocationThreshold = 200 {product} {default}
java -XX:+PrintCompilation -XX:+BackgroundCompilation src/Tier3InvocationThreshold.java 200 | grep Tier3InvocationThreshold
java -XX:+PrintCompilation -XX:+BackgroundCompilation src/Tier3InvocationThreshold.java 255 | grep Tier3InvocationThreshold
java -XX:+PrintCompilation -XX:+BackgroundCompilation src/Tier3InvocationThreshold.java 256 | grep Tier3InvocationThreshold
457 1214 3 Tier3InvocationThreshold::invoke (6 bytes)
java -XX:+PrintCompilation -XX:+BackgroundCompilation -XX:Tier3InvocationThreshold=1000 src/Tier3InvocationThreshold.java 1023 | grep Tier3InvocationThreshold
java -XX:+PrintCompilation -XX:+BackgroundCompilation -XX:Tier3InvocationThreshold=1000 src/Tier3InvocationThreshold.java 1024 | grep Tier3InvocationThreshold
521 900 3 Tier3InvocationThreshold::invoke (6 bytes)
- Does it need to be a power of two?? ->
Tier0BackedgeNotifyFreqLog2^Tier0BackedgeNotifyFreqLog = 2^10 = 1024
Tier3BackEdgeThreshold
java -XX:+UnlockDiagnosticVMOptions -XX:+PrintFlagsFinal -version | grep Tier3BackEdgeThreshold
intx Tier3BackEdgeThreshold = 60000 {product} {default}
java -XX:+PrintCompilation -XX:+BackgroundCompilation src/Tier3BackEdgeThreshold.java 60415 | grep Tier3BackEdgeThreshold
java -XX:+PrintCompilation -XX:+BackgroundCompilation src/Tier3BackEdgeThreshold.java 60416 | grep Tier3BackEdgeThreshold
461 1240 % 3 Tier3BackEdgeThreshold::invoke @ 5 (25 bytes)
- processed using On-Stack-Replacement, switches an implementation of a method (compiled instead of interpreted) during the method execution (it can be still in the loop)
Compilation Log Format
Tier3CompileThreshold
java -XX:+UnlockDiagnosticVMOptions -XX:+PrintFlagsFinal -version | grep -e Tier3MinInvocationThreshold -e Tier3CompileThreshold
intx Tier3CompileThreshold = 2000 {product} {default}
intx Tier3MinInvocationThreshold = 100 {product} {default}
- combines
InvocationThresholdandBackEdgeThreshold - compilation happens when the condition below is met
invocationCount > Tier3MinInvocationThreshold && invocationCount + backEdgeCount > Tier3CompileThreshold
java -XX:+PrintCompilation -XX:+BackgroundCompilation src/Tier3CompileThreshold.java 100 | grep Tier3CompileThreshold [23/01/8| 6:04PM]
java -XX:+PrintCompilation -XX:+BackgroundCompilation src/Tier3CompileThreshold.java 101 | grep Tier3CompileThreshold [23/01/8| 6:28PM]
java -XX:+PrintCompilation -XX:+BackgroundCompilation src/Tier3CompileThreshold.java 102 | grep Tier3CompileThreshold [23/01/8| 6:28PM]
java -XX:+PrintCompilation -XX:+BackgroundCompilation src/Tier3CompileThreshold.java 103 | grep Tier3CompileThreshold [23/01/8| 6:28PM]
471 1220 3 Tier3CompileThreshold::invoke (26 bytes)
petrbouda