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 DC8064C6 for ; Wed, 7 May 2014 05:21:59 +0000 (UTC) Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by smtp1.linuxfoundation.org (Postfix) with ESMTP id 5403920274 for ; Wed, 7 May 2014 05:21:59 +0000 (UTC) From: "Iyer, Sundar" To: Peter Zijlstra , "Rafael J. Wysocki" Date: Wed, 7 May 2014 05:20:59 +0000 Message-ID: <2FABAEF0D3DCAF4F9C9628D6E2F9684533B4C781@BGSMSX102.gar.corp.intel.com> Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Cc: "Brown, Len" , Daniel Lezcano , Ingo Molnar , "ksummit-discuss@lists.linuxfoundation.org" Subject: Re: [Ksummit-discuss] [TECH(CORE?) TOPIC] Energy conservation bias interfaces List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , > -----Original Message----- > From: ksummit-discuss-bounces@lists.linuxfoundation.org [mailto:ksummit- > discuss-bounces@lists.linuxfoundation.org] On Behalf Of Peter Zijlstra > > (http://marc.info/?t=3D139834240600003&r=3D1&w=3D4) it became apparent = that > > 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 It might sound a stupid question, but isn't this entirely dependent on the = platform? A higher performance will translate into better energy only if the "race to= halt" was true and the system/platform had a nice power/performance/energy curve. E.g= . if the task got completed quicker enough (reduced t) to offset the most probably i= ncreased current consumption (increased i @ constant v). Am I wrong? What would happen on a platform, where more performance means using more energy? > > 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 Instead of either energy or performance, would it be easier to look if it were a "just enough performance" metric? Rather than worry about a reduc= ed performance to save energy, it would be IMO better to try to optimize the e= nergy within the constraints of the required performance. Of course, those constr= aints could be changed. e.g. if the display would communicate it doesn't need to refresh more than = 60fps, this could be communicated to the GPU/CPU to control the bias for these sub= -systems accordingly. > > in response to certain "power" events such as "battery is low/critical"= etc. Would I be wrong if I said the thermal throttling is already an example of = this? When the battery is critical/temperature is unbearable, the system cuts dow= n the performance of sub-systems like CPU, display etc. > per-subsystem sounds right to me; I don't care which particular instance = of > graphics cards I have, I want whichever one(s) I have to obey. >=20 > global doesn't make sense, like stated earlier I absolutely detest automa= gic > backlight dimming, whereas I don't particularly care about compute speed = at > all. That calls for highly customized preferences for what to control: in most c= ases the dimmed backlight itself saves a considerable amount of energy which wou= ldn't be matched by a CPU (or a GPU) control. On a battery device, the first pref= erence would be to dim out the screen but still allow the user a good battery life= and=20 user experience. Cheers!