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    • How Tos and Troubleshooting page_name: a-brief-perf-how-to title: Timechart how-to

Developer builds contain a performance analysis command called perf that can be used to create an SVG output file similar to bootchart; the chart shows how CPU cycles and I/O wait times are distributed across processes in the system over time.

Below is a short primer in four lessons describing how to generate and view output from perf timechart.

Lesson 1 - a simple example

  1. Boot Chromium OS, and open a terminal.

  2. Run this command:

    sudo perf timechart record

  3. Run your workload. A workload isn't necessary if all you want to see is a chart of an idle system. :-)

  4. When your workload is done, interrupt the process started in step 2 using ^C, or kill -2.

Explanation: Without arguments, perf timechart record runs forever gathering data, until stopped by SIGINT. Note that only SIGINT works; SIGTERM will kill the process without producing the necessary output. When the command completes, you'll see two new files: perf.data and trace.out.

Lesson 2 - how to generate and view the chart

  1. In the directory where you ran Lesson 1, run this command:

    sudo perf timechart

  2. The output image will be stored in a file named output.svg. Use scp or some equivalent to copy the file to another system for viewing.

Tips for viewing: Some browsers may have trouble displaying the image. The author of timechart recommends the Inkscape image editor:

http://www.inkscape.org/

Inkscape does a good job of displaying the fine details, but it may be a bit slow for the large timechart images. You should exercise patience when opening, magnifying, or scroling images.

Lesson 3 - how to avoid using SIGINT

  1. Run this command:

    sudo perf timechart record sleep 5

  2. Run a workload that will finish within 5 seconds; for longer workloads, use a more appropriate sleep time in step 1.

  3. Generate and view the output as described in Lesson 2.

Explanation: If there are arguments to perf timechart record, the arguments are treated as a command to run as a subprocess of perf. perf gathers data until the process terminates.

If your workload is triggered by a single command, that command can be used in place of ‘sleep 5’. Note that if the workload acts as a daemon (that is, forks a child and exits), perf will terminate with the parent terminates; this likely isn‘t what you’d want.

Lesson 4 - how to get a timechart of system boot

  1. Install bootchart on your workstation. For ubuntu:

    sudo apt-get install bootchart

  2. emerge and install bootchart onto your DUT:

    emerge-$BOARD bootchart &&  cros deploy $DUT bootchart

  3. reboot DUT

    ssh $DUT reboot

  4. bootchart will log events in /var/log/bootchart/boot-<timestamp>.tgz. It will collect data until the DUT upstart sequence has fully completed. Retrieve the archive(s) with

    scp $DUT:/var/log/bootchart/boot-<timestamp>.tgz  /tmp

  5. generate SVG graphics

    F=boot-<timestamp> ; bootchart --format=svg -o $F.svg  $F.tgz

    or in a loop with

    scp $DUT:/var/log/bootchart/boot-*.tgz  . && for i in *; do F=${i%.tgz}; bootchart --format=svg -o "${F}.svg"  "${F}.tgz"; done

    The svg file(s) are ready for viewing.