From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752572AbaAGOLs (ORCPT ); Tue, 7 Jan 2014 09:11:48 -0500 Received: from mail-oa0-f52.google.com ([209.85.219.52]:61181 "EHLO mail-oa0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752397AbaAGOLn (ORCPT ); Tue, 7 Jan 2014 09:11:43 -0500 MIME-Version: 1.0 In-Reply-To: <20140107132220.GZ31570@twins.programming.kicks-ass.net> References: <20131105222752.GD16117@laptop.programming.kicks-ass.net> <1387372431-2644-1-git-send-email-vincent.guittot@linaro.org> <52B87149.4010801@arm.com> <20140106163123.GN31570@twins.programming.kicks-ass.net> <20140107132220.GZ31570@twins.programming.kicks-ass.net> From: Vincent Guittot Date: Tue, 7 Jan 2014 15:11:22 +0100 Message-ID: Subject: Re: [RFC] sched: CPU topology try To: Peter Zijlstra Cc: Dietmar Eggemann , "linux-kernel@vger.kernel.org" , "mingo@kernel.org" , "pjt@google.com" , Morten Rasmussen , "cmetcalf@tilera.com" , "tony.luck@intel.com" , "alex.shi@linaro.org" , "preeti@linux.vnet.ibm.com" , "linaro-kernel@lists.linaro.org" , "paulmck@linux.vnet.ibm.com" , "corbet@lwn.net" , "tglx@linutronix.de" , "len.brown@intel.com" , "arjan@linux.intel.com" , "amit.kucheria@linaro.org" , "james.hogan@imgtec.com" , "schwidefsky@de.ibm.com" , "heiko.carstens@de.ibm.com" Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7 January 2014 14:22, Peter Zijlstra wrote: > On Tue, Jan 07, 2014 at 09:32:04AM +0100, Vincent Guittot wrote: >> On 6 January 2014 17:31, Peter Zijlstra wrote: >> > On Mon, Jan 06, 2014 at 02:41:31PM +0100, Vincent Guittot wrote: >> >> IMHO, these settings will disappear sooner or later, as an example the >> >> idle/busy _idx are going to be removed by Alex's patch. >> > >> > Well I'm still entirely unconvinced by them.. >> > >> > removing the cpu_load array makes sense, but I'm starting to doubt the >> > removal of the _idx things.. I think we want to retain them in some >> > form, it simply makes sense to look at longer term averages when looking >> > at larger CPU groups. >> > >> > So maybe we can express the things in log_2(group-span) or so, but we >> > need a working replacement for the cpu_load array. Ideally some >> > expression involving the blocked load. >> >> Using the blocked load can surely give benefit in the load balance >> because it gives a view of potential load on a core but it still decay >> with the same speed than runnable load average so it doesn't solve the >> issue for longer term average. One way is to have a runnable average >> load with longer time window > > Ah, another way of looking at it is that the avg without blocked > component is a 'now' picture. It is the load we are concerned with right > now. > > The more blocked we add the further out we look; with the obvious limit > of the entire averaging period. > > So the avg that is runnable is right now, t_0; the avg that is runnable + > blocked is t_0 + p, where p is the avg period over which we expect the > blocked contribution to appear. > > So something like: > > avg = runnable + p(i) * blocked; where p(i) \e [0,1] > > could maybe be used to replace the cpu_load array and still represent > the concept of looking at a bigger picture for larger sets. Leaving open > the details of the map p. That needs to be studied more deeply but that could be a way to have a larger picture Another point is that we are using runnable and blocked load average which are the sum of load_avg_contrib of tasks but we are not using the runnable_avg_sum of the cpus which is not the now picture but a average of the past running time (without taking into account task weight) Vincent