Re: cpu governor and cpufreq

[Viresh Kumar <viresh.kumar@linaro.org>]

On 21-04-21, 12:03, Pankaj  Vinodrao Joshi wrote:
> Hi,
> 
> i am trying to explore linux power management and was going through
> cpu governor and freq scaling but i have following doubts can
> someone help me to get it clarified
> 
> 1) i understood that there are different governors implemented in
>    linux kernel like ondemand, userspace etc. and each policy can
>    have different governor for each cpu ,

No. A governor controls an entire policy (policy is used to relate
CPUs, normally all CPUs belonging to a policy are controlled by a
single knob (a single bit in a register), and so they all run on the
same frequency all the time). There is a driver flag
(CPUFREQ_HAVE_GOVERNOR_PER_POLICY), which is required to allow a
different governor for each policy, without it same governor will be
used for all online CPUs.

>    but i want to understand
>    how these policies are interlinked with drivers, how they will
>    use governors ?

Policies are created (or provided by the drivers), they mainly
provide a function to change frequency (only one of target(),
target_index() or setpolicy()).

A governor is not related to a driver at all, it just tells how and
when we are going to change the frequency, and cpufreq core uses the
above callback to make that change.

> 2) which governor to use is this written in the driver code ?

Again, governor doesn't have anything to do with the driver.

> How i should verify which policy driver is using ?

All the policies are used at the same time, as each CPU needs to be
controlled by a policy..

>    i was going through
>    gpio-brcmstb.c and i was not able to see anything about cpufreq
>    scaling.

-- 
viresh