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

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Message-ID: <20160208133446.GK8294@vireshk>
Date:	Mon, 8 Feb 2016 19:04:46 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	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 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.

> 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.

--
viresh