linux-kernel - Re: [PATCH 2/2] cpufreq: Specify default governor on command line

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Date:   Tue, 16 Jun 2020 14:57:59 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Quentin Perret <qperret@...gle.com>
Cc:     rjw@...ysocki.net, rafael@...nel.org, arnd@...db.de,
        mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        kernel-team@...roid.com, tkjos@...gle.com, adharmap@...eaurora.org
Subject: Re: [PATCH 2/2] cpufreq: Specify default governor on command line

On 16-06-20, 09:31, Quentin Perret wrote:
> Right, so the reason I avoided cpufreq_core_init() was because it is
> called at core_initcall() time, which means I can't really assume the
> governors have been loaded by that time. By waiting for the driver to
> probe before detecting the default gov, we get that nice ordering. But
> yes, it feels odd to have it here :/
> 
> Thinking about it more, the natural fit for this would rather be the
> register/unregister path for governors directly. If that sounds good to
> you (?) I'll try to move it there in v2.

There is another problem here which we need to look at. Any governor
which is built as a module and isn't currently used, should be allowed
to unload. And this needs to be tested by you as well, should be easy
enough.

With the current implementation, you take a reference to the default
governor when the driver is registered and drop it only when the
driver goes away. Which means we won't be able to unload the module of
the governor even if it isn't used. Which is wrong. The solution I
proposed had the same issue as well.

You need to figure out a way where we don't need to keep holding the
module hostage even when it isn't used. I see two ways at least for
the same:

- Do that from the existing place: cpufreq_init_policy().

- And I think this can be done from governor-register/unregister as
  well.

Second one sounds good, if it is feasible to do that.

-- 
viresh