From mboxrd@z Thu Jan 1 00:00:00 1970 From: Viresh Kumar Subject: Re: [PATCH V3 12/13] cpufreq: ondemand: Traverse list of policy_dbs in update_sampling_rate() Date: Mon, 8 Feb 2016 22:50:28 +0530 Message-ID: <20160208172028.GU8294@vireshk> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: "Rafael J. Wysocki" Cc: Rafael Wysocki , Juri Lelli , Lists linaro-kernel , "linux-pm@vger.kernel.org" , Saravana Kannan , Peter Zijlstra , Michael Turquette , Steve Muckle , Vincent Guittot , Morten Rasmussen , dietmar.eggemann@arm.com, Shilpasri G Bhat , Linux Kernel Mailing List List-Id: linux-pm@vger.kernel.org On 08-02-16, 14:32, Rafael J. Wysocki wrote: > The comment still applies. > > Moreover, please extend it to say that this must be called with > dbs_data->mutex held (or it looks racy otherwise). Modified it as: + * + * Simply updating dbs_tuners_int.sampling_rate might not be appropriate here. + * 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, otherwise the governor may change the sampling rate too + * late; up to 1 second later. + * + * Similar logic applies while increasing the sampling rate. And so we need to + * update it with immediate effect. + * + * This must be called with dbs_data->mutex held, otherwise traversing + * policy_dbs_list isn't safe. -- viresh