Chapter 14. Investigating busy CPUs with perf

Prerequisites

• You have the perf user space tool installed. For more information, see Installing perf.

Procedure

• Count the events with CPU count aggregation disabled:

  # perf stat -a -A sleep seconds

  This command displays the count of a default set of common hardware and software events recorded for a time-period of seconds seconds, as dictated by using the sleep command, over each CPU in ascending order, starting with CPU0. As such, it may be useful to specify an event such as cycles:

  # perf stat -a -A -e cycles sleep seconds

Prerequisites

• You have the perf user space tool installed. For more information, see Installing perf.
• There is a perf.data file created with perf record in the current directory. If the perf.data file was created with root access, you need to run perf report with root access too.

Procedure

• Display the contents of the perf.data file for further analysis while sorting by CPU:

  # perf report --sort cpu

  • You can sort by CPU and command to display more detailed information about where CPU time is being spent:

    # perf report --sort cpu,comm

    This example will list commands from all monitored CPUs by total overhead in descending order of overhead usage and identify the CPU the command was executed.

Prerequisites

• You have the perf user space tool installed. For more information, see Installing perf.

Procedure

• Start the perf top interface while sorting by CPU:

  # perf top --sort cpu

  This command lists CPUs and their respective overhead in descending order of overhead usage in real time. You can sort by CPU and command for more detailed information of where CPU time is being spent:

  # perf top --sort cpu,comm

  This command lists commands by total overhead in descending order of overhead usage and identifies the CPU the command was executed on in real time.

Prerequisites

• You have the perf user space tool installed. For more information, see Installing perf.