1

Problem : Run all core on minimum CPU frequency on Intel pstate driver on ubuntu 14.

cpupower  frequency-set --governor performance --max 1300MHz

I am trying to run my cpu cores on different constant frequencies. For this i have chosen performance governor. I have set all of my scaling max frequency range from 1.2GHz to 1.3GHz

# cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_max_freq
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000
1300000

But my limits get overridden and i have no idea why. I tried going through alot of similar problems and could not find anything conclusive.

cpufrequtils 008: cpufreq-info (C) Dominik Brodowski 2004-2009
Report errors and bugs to cpufreq@vger.kernel.org, please.
analyzing CPU 0:
  driver: intel_pstate
  CPUs which run at the same hardware frequency: 0
  CPUs which need to have their frequency coordinated by software: 0
  maximum transition latency: 0.97 ms.
  hardware limits: 1.20 GHz - 3.30 GHz
  available cpufreq governors: performance, powersave
  current policy: frequency should be within 1.20 GHz and 1.30 GHz.
                  The governor "performance" may decide which speed to use
                  within this range.
  current CPU frequency is 1.20 GHz (asserted by call to hardware).
analyzing CPU 1:
  driver: intel_pstate
  CPUs which run at the same hardware frequency: 1
  CPUs which need to have their frequency coordinated by software: 1
  maximum transition latency: 0.97 ms.
  hardware limits: 1.20 GHz - 3.30 GHz
  available cpufreq governors: performance, powersave
  current policy: frequency should be within 1.20 GHz and 1.30 GHz.
                  The governor "performance" may decide which speed to use
                  within this range.
  current CPU frequency is 1.20 GHz (asserted by call to hardware).
analyzing CPU 2:
  driver: intel_pstate
  CPUs which run at the same hardware frequency: 2
  CPUs which need to have their frequency coordinated by software: 2
  maximum transition latency: 0.97 ms.
  hardware limits: 1.20 GHz - 3.30 GHz
  available cpufreq governors: performance, powersave
  current policy: frequency should be within 1.20 GHz and 1.30 GHz.
                  The governor "performance" may decide which speed to use
                  within this range.
  current CPU frequency is 1.20 GHz (asserted by call to hardware).

I think these hardware limitations are imposed (hardware limits: 1.20 GHz - 3.30 GHz) but i donot know how to change these limitations. The bios_limit feature is available in acpi driver but not intel pstate.

Also, i spent ALOT of time on disabling intel pstate on my ubuntu 14 but it does not revert back to acpi. There is some issue in my kernel. I say this because on other machines i am able to revert back to the old kernel. So acpi is not an option.

Does anyone know why these limits are not enforced? As you can see in the image , most cores go way beyond (29GHz) my enforced limit of 1.3GHz https://ibb.co/hOmVfU

some cores exceed the 1.3GHz limit

  • 1
    Your limits do seem to be applied: “current policy: frequency should be within 1.20 GHz and 1.30 GHz.”. For background, see also the comments here — it seems scaling_max_freq can be changed on power events. – Stephen Kitt Sep 10 '18 at 12:40
  • @StephenKitt yes it is applied however when i stress test the cores, almost all cores are able to achieve 2.9GHz as some point or another. This makes me question if the limits are overidden. Please review the image link. – JRD Sep 10 '18 at 13:48
  • What’s the value of scaling_max_freq after the stress test? – Stephen Kitt Sep 10 '18 at 13:59
  • @stephen kitt it stays the same. – JRD Sep 10 '18 at 15:08

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