From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751658AbaAGNWw (ORCPT ); Tue, 7 Jan 2014 08:22:52 -0500 Received: from merlin.infradead.org ([205.233.59.134]:57897 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751080AbaAGNWs (ORCPT ); Tue, 7 Jan 2014 08:22:48 -0500 Date: Tue, 7 Jan 2014 14:22:20 +0100 From: Peter Zijlstra To: Vincent Guittot 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" Subject: Re: [RFC] sched: CPU topology try Message-ID: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 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.