From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTP id AD84B8CC for ; Tue, 6 May 2014 16:04:39 +0000 (UTC) Received: from collaborate-mta1.arm.com (fw-tnat.austin.arm.com [217.140.110.23]) by smtp1.linuxfoundation.org (Postfix) with ESMTP id 8E9FE2026F for ; Tue, 6 May 2014 16:04:38 +0000 (UTC) Date: Tue, 6 May 2014 17:04:25 +0100 From: Morten Rasmussen To: Peter Zijlstra Message-ID: <20140506160425.GC2779@e103034-lin> References: <1998761.B2k0A5OtQR@vostro.rjw.lan> <20140506134909.GM11096@twins.programming.kicks-ass.net> <20140506145125.GB2779@e103034-lin> <20140506153956.GV26782@laptop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140506153956.GV26782@laptop.programming.kicks-ass.net> Cc: Len Brown , "ksummit-discuss@lists.linuxfoundation.org" , Daniel Lezcano , Amit Kucheria , Ingo Molnar Subject: Re: [Ksummit-discuss] [TECH(CORE?) TOPIC] Energy conservation bias interfaces List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, May 06, 2014 at 04:39:56PM +0100, Peter Zijlstra wrote: > On Tue, May 06, 2014 at 03:51:25PM +0100, Morten Rasmussen wrote: > > On Tue, May 06, 2014 at 02:49:09PM +0100, Peter Zijlstra wrote: > > > On Tue, May 06, 2014 at 02:54:03PM +0200, Rafael J. Wysocki wrote: > > > > Hi All, > > > > > > > > During a recent discussion on linux-pm/LKML regarding the integration of the > > > > scheduler with cpuidle (http://marc.info/?t=139834240600003&r=1&w=4) it became > > > > apparent that the kernel might benefit from adding interfaces to let it know > > > > how far it should go with saving energy, possibly at the expense of performance. > > > > > > > > First of all, it would be good to have a place where subsystems and device > > > > drivers can go and check what the current "energy conservation bias" is in > > > > case they need to make a decision between delivering more performance and > > > > using less energy. Second, it would be good to provide user space with > > > > a means to tell the kernel whether it should care more about performance or > > > > energy. Finally, it would be good to be able to adjust the overall "energy > > > > conservation bias" automatically in response to certain "power" events such > > > > as "battery is low/critical" etc. > > > > > > > > It doesn't seem to be clear currently what level and scope of such interfaces > > > > is appropriate and where to place them. Would a global knob be useful? Or > > > > should they be per-subsystem, per-driver, per-task, per-cgroup etc? > > > > > > per-task and per-cgroup doesn't seem to make sense to me; its the > > > hardware that consumes energy. > > > > True. But performance requirements are associated with tasks or groups > > of tasks. We also need an interface to get input from userspace to tell > > us when it is acceptable to potentially loose performance to save > > energy. IIUC, that is Rafael's second point above. > > That's the QoS thing. While related I don't think we should confuse the > two. Fully agree. We need both.