From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthias Kaehlcke Subject: Re: [PATCH 1/3] drivers: base: Add frequency constraint infrastructure Date: Fri, 18 Jan 2019 14:45:34 -0800 Message-ID: <20190118224534.GC261387@google.com> References: <20190118010305.GX261387@google.com> <20190118100234.kq37hc4ldujqvvrb@vireshk-i7> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Content-Disposition: inline In-Reply-To: <20190118100234.kq37hc4ldujqvvrb@vireshk-i7> Sender: linux-kernel-owner@vger.kernel.org To: Viresh Kumar Cc: Rafael Wysocki , Greg Kroah-Hartman , "Rafael J. Wysocki" , Viresh Kumar , linux-pm@vger.kernel.org, Vincent Guittot , linux-kernel@vger.kernel.org List-Id: linux-pm@vger.kernel.org On Fri, Jan 18, 2019 at 03:32:34PM +0530, Viresh Kumar wrote: > On 17-01-19, 17:03, Matthias Kaehlcke wrote: > > On Fri, Jan 11, 2019 at 02:48:34PM +0530, Viresh Kumar wrote: > > > +static void fcs_update(struct freq_constraints *fcs, struct freq_pair *freq, > > > + enum fc_event event) > > > +{ > > > + mutex_lock(&fcs->lock); > > > + > > > + if (_fcs_update(fcs, freq, event)) { > > > + if (fcs->callback) > > > + schedule_work(&fcs->work); > > > > IIUC the constraints aren't applied until the callback is executed. I > > wonder if a dedicated workqueue should be used instead of the system > > one, to avoid longer delays from other kernel entities that might > > 'misbehave'. Especially for thermal constraints we want a quick > > response. > > I thought the system workqueue should be fast enough, it contains > multiple threads which can all run in parallel and service this work. Ok, I was still stuck at the old one thread per CPU model, where a slow work would block other items in the same workqueue until it finishes execution. After reading a bit through Documentation/core-api/workqueue.rst I agree that a system workqueue is probably fast enough. It might be warranted though to use system_highpri_wq here. Cheers Matthias