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linuxperformanceperformance-testingperfjailhouse

How to trace the list of PIDs running on a specific core?

I'm trying to run a program on a dedicated core in Linux. (I know Jailhouse is a good way to do so, but I have to use off-the-shelf Linux. :-( )

Other processes, such as interrupt handlers, kernel threads, service progresses, may also run on the dedicated core occasionally. I want to disable as many such processes as possible. To do that, I need first pin down the list of processes that may run on the dedicated core.

My question is:

Is there any existing tools that I can use to trace the list of PIDs or processes that run on a specific core over a time interval?

Thank you very much for your time and help in this question!

Solution

  • TL;DR Dirty hacky solution.

    DISCLAIMER: At some point stops working "column: line too long" :-/

    Copy this to: core-pids.sh

    #!/bin/bash

TARGET_CPU=0

touch lastPIDs
touch CPU_PIDs

while true; do
  ps ax -o cpuid,pid | tail -n +2 | sort | xargs -n 2 | grep -E "^$TARGET_CPU" | awk '{print $2}' > lastPIDs
  for i in {1..100}; do printf "#\n" >> lastPIDs; done
  cp CPU_PIDs aux
  paste lastPIDs aux > CPU_PIDs
  column -t CPU_PIDs > CPU_PIDs.humanfriendly.tsv
  sleep 1
done

    Then

    chmod +x core-pids.sh
./core-pids.sh

    Then open CPU_PIDs.humanfriendly.tsv with your favorite editor, and ¡inspect!

    The key is in the "ps -o cpuid,pid" bit, for more detailed info, please comment. :D

    Explanation

    Infinite loop with

    • ps -o cpuid,pid | tail -n +2 | sort | xargs -n 2 | grep -E "^$TARGET_CPU" | awk '{print $2}' > lastPIDs
      • ps ax -o cpuid,pid
        • Show pid's associated to CPU
      • tail -n +2
        • remove headers
      • sort
        • sort by cpuid
      • xargs -n 2
        • remove white spaces at begging
      • grep -E "^$TARGET_CPU"
        • filter by CPU id
      • awk '{print $2}'
        • get pid column
      • > lastPIDs
        • output to file those las pid's for the target CPU id
    • for i in {1..10}; do printf "#\n" >> lastPIDs; done
      • hack for pretty .tsv print with the "columns -t" command
    • cp CPU_PIDs aux
      • CPU_PIDs holds the whole timeline, we copy it to aux file to allow the next command to use it as input and output
    • paste lastPIDs aux > CPU_PIDs
      • Append lastPIDs columns to the whole timeline file CPU_PIDs
    • column -t CPU_PIDs > CPU_PIDs.humanfriendly.tsv
      • pretty print whole timeline CPU_PIDs file

    Attribution