linux-kernel - Re: [PATCH V3 12/13] cpufreq: ondemand: Traverse list of policy_dbs in update_sampling

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Message-ID: <CAJZ5v0iS_YKyuZhbP1cA7cVEFZZAH1h0867sJEeFzTUkMikmwg@mail.gmail.com>
Date:	Mon, 8 Feb 2016 14:37:03 +0100
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	Rafael Wysocki <rjw@...ysocki.net>,
	Juri Lelli <juri.lelli@....com>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Saravana Kannan <skannan@...eaurora.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Michael Turquette <mturquette@...libre.com>,
	Steve Muckle <steve.muckle@...aro.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	dietmar.eggemann@....com,
	Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 12/13] cpufreq: ondemand: Traverse list of policy_dbs
 in update_sampling_rate()

On Mon, Feb 8, 2016 at 2:34 PM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> On 08-02-16, 14:32, Rafael J. Wysocki wrote:
>> > - * If new rate is smaller than the old, simply updating
>> > - * dbs_tuners_int.sampling_rate might not be appropriate. For example, if the
>> > - * original sampling_rate was 1 second and the requested new sampling rate is 10
>> > - * ms because the user needs immediate reaction from ondemand governor, but not
>> > - * sure if higher frequency will be required or not, then, the governor may
>> > - * change the sampling rate too late; up to 1 second later. Thus, if we are
>> > - * reducing the sampling rate, we need to make the new value effective
>> > - * immediately.
>>
>> The comment still applies.
>
> Why? It talks about the case where we have reduced sampling rate, but
> that's not the case anymore. We *always* update sample_delay_ns now.

But the comment explains *why* we do that, doesn't it?

If it doesn't apply, then why do we need this function at all?

>> Moreover, please extend it to say that this must be called with
>> dbs_data->mutex held (or it looks racy otherwise).
>
> Yeah, that can be done.


OK

Thanks,
Rafael