From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S937727AbdEWUaZ (ORCPT ); Tue, 23 May 2017 16:30:25 -0400 Received: from merlin.infradead.org ([205.233.59.134]:44716 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1763670AbdEWUaP (ORCPT ); Tue, 23 May 2017 16:30:15 -0400 Date: Tue, 23 May 2017 22:29:56 +0200 From: Peter Zijlstra To: Juri Lelli Cc: mingo@redhat.com, rjw@rjwysocki.net, viresh.kumar@linaro.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, tglx@linutronix.de, vincent.guittot@linaro.org, rostedt@goodmis.org, luca.abeni@santannapisa.it, claudio@evidence.eu.com, tommaso.cucinotta@santannapisa.it, bristot@redhat.com, mathieu.poirier@linaro.org, tkjos@android.com, joelaf@google.com, andresoportus@google.com, morten.rasmussen@arm.com, dietmar.eggemann@arm.com, patrick.bellasi@arm.com Subject: Re: [PATCH RFC 0/8] SCHED_DEADLINE freq/cpu invariance and OPP selection Message-ID: <20170523202956.7a2q4ysbqbnaik3n@hirez.programming.kicks-ass.net> References: <20170523085351.18586-1-juri.lelli@arm.com> <20170523202321.3bygt6ydyiy5xief@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170523202321.3bygt6ydyiy5xief@hirez.programming.kicks-ass.net> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 23, 2017 at 10:23:21PM +0200, Peter Zijlstra wrote: > On Tue, May 23, 2017 at 09:53:43AM +0100, Juri Lelli wrote: > > > A point that is still very much up for discussion (more that the others :) is > > how we implement frequency/cpu scaling. SCHED_FLAG_RECLAIM tasks only need > > grub_reclaim(), as the function already scales their reservation runtime > > considering other reservations and maximum bandwidth a CPU has to offer. > > However, for normal !RECLAIM tasks multiple things can be implemented which > > seem to make sense: > > > > - don't scale at all: normal tasks will only get a % of CPU _time_ as granted > > by AC > > - go to max as soon as a normal task in enqueued: this because dimensioning of > > parameters is usually done at max OPP/biggest CPU and normal task assume > > that this is always the condition when they run > > - scale runtime acconding to current frequency and max CPU capacity: this is > > what this set is currently implementing > > > > Opinions? > > > So I'm terribly confused... > > By using the active bandwidth to select frequency we effectively > reduce idle time (to 0 if we had infinite granular frequency steps and > no margins). When all DL tasks consume their full reservation. > So !RECLAIM works as expected. They get the time they reserved, since > that was taken into account by active bandwidth. > > And RECLAIM works, since that only promises to (re)distribute idle time, > and if there is none that is an easy task. And if they don't, there will thus be some idle time to redistribute and that, again, still works as expected.