From mboxrd@z Thu Jan 1 00:00:00 1970 From: Catalin Marinas Subject: Re: [RFC][PATCH v5 00/14] sched: packing tasks Date: Mon, 11 Nov 2013 23:43:23 +0000 Message-ID: References: <1382097147-30088-1-git-send-email-vincent.guittot@linaro.org> <20131111165453.GB4586@e103034-lin> <20131111183142.GF29572@arm.com> <52812F6D.8090404@linux.intel.com> Mime-Version: 1.0 (Mac OS X Mail 7.0 \(1822\)) Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mail-wi0-f171.google.com ([209.85.212.171]:41473 "EHLO mail-wi0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753583Ab3KKXnk convert rfc822-to-8bit (ORCPT ); Mon, 11 Nov 2013 18:43:40 -0500 In-Reply-To: <52812F6D.8090404@linux.intel.com> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Arjan van de Ven Cc: Morten Rasmussen , Vincent Guittot , linux-kernel , Peter Zijlstra , Ingo Molnar , Paul Turner , Chris Metcalf , Tony Luck , "alex.shi@intel.com" , Preeti U Murthy , linaro-kernel , "len.brown@intel.com" , "l.majewski@samsung.com" , Jonathan Corbet , "Rafael J. Wysocki" , Paul McKenney , "linux-pm@vger.kernel.org" On 11 Nov 2013, at 19:26, Arjan van de Ven wrot= e: > On 11/11/2013 10:31 AM, Catalin Marinas wrote: >> I agree, we can't rely on the requested C-state but the_actual_ sta= te >> and this means querying the hardware driver. Can we abstract this vi= a >> some interface which provides the cost of waking up a CPU? This coul= d >> take into account the state of the other CPUs in the cluster and the >> scheduler is simply concerned with the wake-up costs. >=20 > can you even query this without actually waking up the cpu and asking= ??? Even if you don=92t have additional hardware to query the state of a CP= U without waking it up, we could have a per-CPU variable storing the actual C-states as selected by the arch backend. This doesn=92t need t= o be precise but lets say only 90% accurate would probably be enough for the scheduler. Catalin