linux-kernel - Re: [PATCH 3/6] cpufreq: governor: Drop min_sampling

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Date:   Fri, 30 Jun 2017 09:04:25 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Dominik Brodowski <linux@...inikbrodowski.net>
Cc:     Rafael Wysocki <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] cpufreq: governor: Drop min_sampling_rate

On 29-06-17, 20:01, Dominik Brodowski wrote:
> On Thu, Jun 29, 2017 at 04:29:06PM +0530, Viresh Kumar wrote:
> > The cpufreq core and governors aren't supposed to set a limit on how
> > fast we want to try changing the frequency. This is currently done for
> > the legacy governors with help of min_sampling_rate.
> > 
> > At worst, we may end up setting the sampling rate to a value lower than
> > the rate at which frequency can be changed and then one of the CPUs in
> > the policy will be only changing frequency for ever.
> 
> Is it safe to issue requests to change the CPU frequency so frequently,

Well, I assumed so. I am not sure the hardware would break though.
Overheating ?

> even
> on historic hardware such as speedstep-{ich,smi,centrino}? In the past,
> these checks more or less disallowed the running of dynamic frequency
> scaling at least on speedstep-smi[*],

We must by doing dynamic freq scaling even without this patch. I don't
see why you say the above then.

All we do here is that we get rid of the limit on how soon we can
change the freq again.

> but maybe on a few other platforms as
> well. That's why I am curious on whether this may break systems potentially
> on a hardware level if the hardware was not designed to do dynamic frequency
> scaling (and not just frequency switches on battery/AC).

Honestly I am not sure if any hardware can break or not, just because
of this commit.

-- 
viresh