[Discuss] linux cpu governors

[dsr at randomstring.org (Dan Ritter)]

On Tue, Jan 12, 2016 at 10:00:18AM -0500, Matthew Gillen wrote:
> Recent kernels (not sure exactly when this started) have been driving
> me crazy.
> For reference: Machine: Dell Precision with Intel Core i5
> OS: Fedora 23 (kernel 4.2.8-300.fc23.x86_64)
> 
> When running on battery, everything is fine when using the default
> "powersave" governor.  Lately though, if I don't use the 180W power
> supply that came with the computer (e.g. because I don't want that
> beast in my travel bag), the kernel seems to be restricting CPU
> speeds to something outside of what the governor claims to be
> managing.
> 
> Here's what I mean:
> $cat /proc/cpuinfo
>   processor       : 0
>   vendor_id       : GenuineIntel
>   cpu family      : 6
>   model           : 60
>   model name      : Intel(R) Core(TM) i5-4340M CPU @ 2.90GHz
>   cpu MHz         : 365.332
> ...
> $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver
>  intel_pstate
> $cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
>  powersave
> $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
> 3600000
> $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
> 800000
> $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq
> 367257
> 

The problem is in the intel_pstate governor.

https://www.kernel.org/doc/Documentation/cpu-freq/intel-pstate.txt

....

For contemporary Intel processors, the frequency is controlled by the
processor itself and the P-states exposed to software are related to
performance levels.  The idea that frequency can be set to a single
frequency is fiction for Intel Core processors.
.....

-dsr-