Chapter 34. Analyzing application performance

Procedure

• Collect system-wide performance statistics.

  # perf record -a
  ^C[ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.725 MB perf.data (~31655 samples) ]

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  In this example, all CPUs are denoted with the -a option, and the process was terminated after a few seconds. The results show that it collected 0.725 MB of data and stored it to a newly-created perf.data file.

Verification

• Ensure that the results file was created.

  # ls
  perf.data

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• Dynamic Shared Objects (DSOs), such as binaries and libraries, are already present in the analysis system, such as the ~/.debug/ cache.
• Both systems have the same set of binaries.

Procedure

• Analyze the results directly from the perf.data file or from an archived tarball.

  # perf report

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  The output of the report is sorted according to the maximum CPU usage in percentage by the application. It shows if the sample has occurred in the kernel or user space of the process.

  The report shows information about the module from which the sample was taken:

  • A kernel sample that did not take place in a kernel module is marked with the notation [kernel.kallsyms].
  • A kernel sample that took place in the kernel module is marked as [module], [ext4].

  • For a process in user space, the results might show the shared library linked with the process.

    The report denotes whether the process also occurs in kernel or user space.

  • The result [.] indicates user space.
  • The result [k] indicates kernel space.

  Finer grained details are available for review, including data appropriate for experienced perf developers.

Procedure

• List pre-defined hardware and software events:

  # perf list
  List of pre-defined events (to be used in -e):
    cpu-cycles OR cycles                               [Hardware event]
    stalled-cycles-frontend OR idle-cycles-frontend    [Hardware event]
    stalled-cycles-backend OR idle-cycles-backend      [Hardware event]
    instructions                                       [Hardware event]
    cache-references                                   [Hardware event]
    cache-misses                                       [Hardware event]
    branch-instructions OR branches                    [Hardware event]
    branch-misses                                      [Hardware event]
    bus-cycles                                         [Hardware event]
  
    cpu-clock                                          [Software event]
    task-clock                                         [Software event]
    page-faults OR faults                              [Software event]
    minor-faults                                       [Software event]
    major-faults                                       [Software event]
    context-switches OR cs                             [Software event]
    cpu-migrations OR migrations                       [Software event]
    alignment-faults                                   [Software event]
    emulation-faults                                   [Software event]
    ...[output truncated]...

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