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Adel Ahmed
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PostPosted: Mon Nov 08, 2021 9:51 am    Post subject: unable to change cpu governors[solved] Reply with quote

I found out that my laptop has been using the performance cpu governor, I wanted to change that to ondemand or conservative but I get the following:

Code:
samsung /etc/laptop-mode # cat  /sys/devices/system/cpu/cpu3/cpufreq/scaling_available_governors
performance powersave
samsung /etc/laptop-mode # echo conservative > /sys/devices/system/cpu/cpu3/cpufreq/scaling_governor
-su: echo: write error: Invalid argument

samsung /usr/src/linux # grep -i conservative /usr/src/linux/.config
CONFIG_CPU_FREQ_DEFAULT_GOV_CONSERVATIVE=y
CONFIG_CPU_FREQ_GOV_CONSERVATIVE=y

samsung /usr/src/linux # grep -i powersave /usr/src/linux/.config
# CONFIG_CPU_FREQ_DEFAULT_GOV_POWERSAVE is not set
# CONFIG_CPU_FREQ_GOV_POWERSAVE is not set
# CONFIG_PCIEASPM_POWERSAVE is not set

samsung ~ # uname -v
#22 SMP Mon Nov 8 11:40:38 EET 2021

I do not get how powersave is available although it is not set in my kernel.
I have compiled the kernel several times and made sure I'm booting from that kernel. any idea what I can do about this?


Last edited by Adel Ahmed on Thu Nov 11, 2021 7:28 am; edited 1 time in total
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Zucca
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PostPosted: Mon Nov 08, 2021 10:07 am    Post subject: Reply with quote

Make sure you have those setting enabled on running kernel.
Check with:
Code:
zfgrep CONFIG_CPU_FREQ_GOV_ /proc/config.gz

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pietinger
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PostPosted: Mon Nov 08, 2021 2:16 pm    Post subject: Reply with quote

Do you have an Intel CPU ?

If yes: What says "cat /sys/devices/system/cpu/intel_pstate/status" ?

If "active" then you have the P-State gouvernor and you cant select with the old intel gouvernor. NOTE: intel_pstate driver supports only two governors: powersave and performance

See more here: https://wiki.archlinux.org/title/CPU_frequency_scaling
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Adel Ahmed
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PostPosted: Mon Nov 08, 2021 4:40 pm    Post subject: Reply with quote

correct:
Code:
samsung /usr/src/linux # cat /sys/devices/system/cpu/intel_pstate/status
active


that is disappointing, anyway I can save power with this processor?
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pietinger
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PostPosted: Mon Nov 08, 2021 5:00 pm    Post subject: Reply with quote

Adel Ahmed wrote:
[...] anyway I can save power with this processor?

Yes, just use "powersave"-gouvernor
(I think Intel thought you only need either "maximum speed" or "minimum power")
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figueroa
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PostPosted: Tue Nov 09, 2021 3:44 am    Post subject: Reply with quote

Try:
Code:
# cpupower frequency-info
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:  Cannot determine or is not supported.
  hardware limits: 1.60 GHz - 3.80 GHz
  available cpufreq governors: performance powersave
  current policy: frequency should be within 1.60 GHz and 3.80 GHz.
                  The governor "powersave" may decide which speed to use
                  within this range.
  current CPU frequency: Unable to call hardware
  current CPU frequency: 1.60 GHz (asserted by call to kernel)
  boost state support:
    Supported: yes
    Active: yes
    3500 MHz max turbo 4 active cores
    3600 MHz max turbo 3 active cores
    3700 MHz max turbo 2 active cores
    3800 MHz max turbo 1 active cores


and:
Code:
# grep -i POWERS /usr/src/linux/.config
CONFIG_CPU_FREQ_DEFAULT_GOV_POWERSAVE=y
CONFIG_CPU_FREQ_GOV_POWERSAVE=y


ADDED: Runs fast, cool, well modulated.
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Goverp
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PostPosted: Tue Nov 09, 2021 8:40 am    Post subject: Reply with quote

pietinger wrote:
Adel Ahmed wrote:
[...] anyway I can save power with this processor?

Yes, just use "powersave"-gouvernor
(I think Intel thought you only need either "maximum speed" or "minimum power")

I thought "ondemand" (or the newer "schedutil") were reckoned to provide better value for money (or cycles). Basically, powersave just makes your machine run slower, so you have to wait longer for the same workload to finish, and therefore you used more power running everything that isn't the cpu. But this may be for non-Intel cpus.
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pietinger
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PostPosted: Tue Nov 09, 2021 9:42 am    Post subject: Reply with quote

Goverp wrote:
[...] But this may be for non-Intel cpus.

Yes, maybe, but I dont know because I know only Intel CPUs. And for an Intel there is the recommendation to use P-state when having Sandy Bridge and later generations.

PS.: See more here: https://www.kernel.org/doc/html/latest/admin-guide/pm/intel_pstate.html


Last edited by pietinger on Tue Nov 09, 2021 9:50 am; edited 1 time in total
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dmpogo
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PostPosted: Tue Nov 09, 2021 9:48 am    Post subject: Reply with quote

What are you talking about ? Intel pstate driver provides its own, hardware implemented drivers. They are called performance and powerstate, but they are not the same as cpufreq scaling drivers. cpufreq (with its own performate/powersave/ondemand etc) is bypassed entirely if intel pstate is used. Intel performance/powersave amounts to setting some bit in CPU and the rest is in hardware.

https://www.kernel.org/doc/html/v4.12/admin-guide/pm/intel_pstate.html
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figueroa
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PostPosted: Tue Nov 09, 2021 3:31 pm    Post subject: Reply with quote

@dmpogo -- what is WHO talking about? That would add clarity.
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dmpogo
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PostPosted: Tue Nov 09, 2021 5:45 pm    Post subject: Reply with quote

figueroa wrote:
@dmpogo -- what is WHO talking about? That would add clarity.


Yep, sorry, I misfired aimlessly :) It was meant to express general confusion about the discussion
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Adel Ahmed
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PostPosted: Thu Nov 11, 2021 7:27 am    Post subject: Reply with quote

thanks everyone I will set my governor to powersave
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dmpogo
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PostPosted: Thu Nov 11, 2021 7:36 pm    Post subject: Reply with quote

Adel Ahmed wrote:
thanks everyone I will set my governor to powersave


Just keep in mind that intel p_state driver with "performance" setting does not keep the CPU frequency fixed either. p_state switching is very fast, it adjusts frequency continuously. "Performance" just do it with a somewhat performance oriented bias while powersave biases more towards saving power. This is in contrast to cpufreq "performance" which I think just kepts CPU at maximum frequency.
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pietinger
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PostPosted: Thu Nov 11, 2021 9:29 pm    Post subject: Reply with quote

dmpogo wrote:
Just keep in mind that intel p_state driver with "performance" setting does not keep the CPU frequency fixed either. p_state switching is very fast, it adjusts frequency continuously.

Yes.

Let me add for "performance": If your Intel processor is capable of doing an overboost (like mine i7), then you will see your cpu frequency at maximum (mine: 4.000) when CPU is idle, and it goes down to maximum (mine: 3.700 without boost) when having high cpu load.
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