Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752650AbaAGPhT (ORCPT ); Tue, 7 Jan 2014 10:37:19 -0500 Received: from fw-tnat.austin.arm.com ([217.140.110.23]:39226 "EHLO collaborate-mta1.arm.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751358AbaAGPhP (ORCPT ); Tue, 7 Jan 2014 10:37:15 -0500 Date: Tue, 7 Jan 2014 15:37:15 +0000 From: Morten Rasmussen To: Vincent Guittot Cc: Peter Zijlstra , Dietmar Eggemann , "linux-kernel@vger.kernel.org" , "mingo@kernel.org" , "pjt@google.com" , "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: <20140107153715.GG2936@e103034-lin> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 07, 2014 at 02:11:22PM +0000, Vincent Guittot wrote: > 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 The blocked load discussion comes up again :) I totally agree that blocked load would be useful, but only if we get the priority problem sorted out. Blocked load is the sum of load_contrib of blocked tasks, which means that a tiny high priority task can have a massive contribution to the blocked load. > > > > 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. Figuring out p is the difficult bit. AFAIK, with blocked load in its current form we don't have any clue when a task will reappear. > > That needs to be studied more deeply but that could be a way to have a > larger picture Agree. > > 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) Yes. The rq runnable_avg_sum is an excellent longer term load indicator. It can't be compared with the runnable and blocked load though. The other alternative that I can think of is to introduce an unweighted alternative to blocked load. That is, sum of load_contrib/priority. Morten -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/