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arthas/tutorials/katacoda/command-thread-en/CPU-ratios-calculate.md
gongdewei 503e0de6b4
improve dashboard/thread cpu time sample (#1501) 
* dashboard command support native thread, delta time
* thread command support --all option
2020-09-22 22:18:51 +08:00

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How the CPU ratios are calculated?

The cpu ratios here is similar to the thread %CPU of the linux command top -H -p <pid>. During a sampling interval, the ratio of the incremental cpu time of each thread in the current JVM to the sampling interval time.

Working principle description:

  • Do the first sampling, get the CPU time of all threads ( by calling java.lang.management.ThreadMXBean#getThreadCpuTime() and sun.management.HotspotThreadMBean.getInternalThreadCpuTimes() )
  • Sleep and wait for an interval (the default is 200ms, the interval can be specified by -i)
  • Do the second sampling, get the CPU time of all threads, compare the two sampling data, and calculate the incremental CPU time of each thread
  • Thread CPU usage ratio = Thread increment CPU time / Sampling interval time * 100%

Note: this operation consumes CPU time too (getThreadCpuTime is time-consuming), therefore it is possible to observe Arthas's thread appears in the list. To avoid this, try to increase sample interval, for example: 5000 ms.

Another way to view the thread cpu usage of the Java process, show-busy-java-threads can come to help.