[Bug 1889668] Re: set-cpufreq error when cpu is offline

[scottku]

** Description changed:

- I have hyperthreading disabled on my Ubuntu 20.04 machine, which makes
+ I have hyperthreading disabled on my Ubuntu 19.10 machine, which makes
  some processors in /sys/devices/system/cpu/cpu* have their "online" set
  to 0.
  
  However, when the for-loop in /lib/systemd/set-cpufreq iterates over the
  processors, it doesn't check if the processor is online before trying to
  write the governor name into scaling_governor.
+ 
+ The script appears to have the same bug in Ubuntu 20.04.
  
  I modified the script to print the cpu it is trying to set before doing so, and I get the following:
  Setting powersave scheduler for all CPUs
  /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
  /sys/devices/system/cpu/cpu1/cpufreq/scaling_governor
  /sys/devices/system/cpu/cpu10/cpufreq/scaling_governor
  /lib/systemd/set-cpufreq: 43: echo: echo: I/O error
  
  Since the script doesn't continue to try other processors in the loop,
  it means that only cpu0 and cpu1 on my machine get set to powersave and
  the others remain with the performance governor. The cpufreq-info
  command confirms this.
  
  Checking if the processor has online==1 before writing, or putting the
  echo within a "set +e" "set -e" pair would fix the problem (although the
  latter approach would still print error messages).

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https://bugs.launchpad.net/bugs/1889668

Title:
  set-cpufreq error when cpu is offline

Status in systemd package in Ubuntu:
  New

Bug description:
  I have hyperthreading disabled on my Ubuntu 19.10 machine, which makes
  some processors in /sys/devices/system/cpu/cpu* have their "online"
  set to 0.

  However, when the for-loop in /lib/systemd/set-cpufreq iterates over
  the processors, it doesn't check if the processor is online before
  trying to write the governor name into scaling_governor.

  The script appears to have the same bug in Ubuntu 20.04.

  I modified the script to print the cpu it is trying to set before doing so, and I get the following:
  Setting powersave scheduler for all CPUs
  /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
  /sys/devices/system/cpu/cpu1/cpufreq/scaling_governor
  /sys/devices/system/cpu/cpu10/cpufreq/scaling_governor
  /lib/systemd/set-cpufreq: 43: echo: echo: I/O error

  Since the script doesn't continue to try other processors in the loop,
  it means that only cpu0 and cpu1 on my machine get set to powersave
  and the others remain with the performance governor. The cpufreq-info
  command confirms this.

  Checking if the processor has online==1 before writing, or putting the
  echo within a "set +e" "set -e" pair would fix the problem (although
  the latter approach would still print error messages).

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