From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752604AbbCXNAW (ORCPT ); Tue, 24 Mar 2015 09:00:22 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:45543 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752580AbbCXNAS (ORCPT ); Tue, 24 Mar 2015 09:00:18 -0400 Date: Tue, 24 Mar 2015 14:00:00 +0100 From: Peter Zijlstra To: Morten Rasmussen Cc: Sai Gurrappadi , "mingo@redhat.com" , "vincent.guittot@linaro.org" , Dietmar Eggemann , "yuyang.du@intel.com" , "preeti@linux.vnet.ibm.com" , "mturquette@linaro.org" , "nico@linaro.org" , "rjw@rjwysocki.net" , Juri Lelli , "linux-kernel@vger.kernel.org" Subject: Re: [RFCv3 PATCH 33/48] sched: Energy-aware wake-up task placement Message-ID: <20150324130000.GM23123@twins.programming.kicks-ass.net> References: <1423074685-6336-1-git-send-email-morten.rasmussen@arm.com> <1423074685-6336-34-git-send-email-morten.rasmussen@arm.com> <550368F4.5050905@nvidia.com> <20150316144722.GA13019@e105550-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150316144722.GA13019@e105550-lin.cambridge.arm.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 16, 2015 at 02:47:23PM +0000, Morten Rasmussen wrote: > > Also, this heuristic for determining sg_target is a big little > > assumption. I don't think it is necessarily correct to assume that this > > is true for all platforms. This heuristic should be derived from the > > energy model for the platform instead. > > I have had the same thought, but I ended up making that assumption since > I holds for the for the few platforms I have data for and it simplified > the code a lot. I think we can potentially remove this assumption later. So the thing is; if we know all the possible behavioural modes of our system we could pre compute which are applicable to the system at hand. All we need is a semi formal definition of our model and a friendly mathematician who can do the bifurcation analysis to find the modal boundaries and their parameters. I suspect there is a limited number of modes and parameters and if we implement all we just need to select the right ones, this could save a lot of runtime computation. But yes, we don't need to start with that, we can do the brute force thing for a while.