From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756414AbaAHMn2 (ORCPT ); Wed, 8 Jan 2014 07:43:28 -0500 Received: from merlin.infradead.org ([205.233.59.134]:56678 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756206AbaAHMn0 (ORCPT ); Wed, 8 Jan 2014 07:43:26 -0500 Date: Wed, 8 Jan 2014 13:42:53 +0100 From: Peter Zijlstra To: Morten Rasmussen Cc: Vincent Guittot , 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: <20140108124253.GC31570@twins.programming.kicks-ass.net> References: <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> <20140107141059.GY3694@twins.programming.kicks-ass.net> <20140107154154.GH2936@e103034-lin> <20140107204951.GD2480@laptop.programming.kicks-ass.net> <20140108123534.GI2936@e103034-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140108123534.GI2936@e103034-lin> 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 Wed, Jan 08, 2014 at 12:35:34PM +0000, Morten Rasmussen wrote: > > The harder case is where all 3 tasks are of equal weight; in which case > > fairness would mandate we (slowly) rotate the tasks such that they all > > get 2/3 time -- we also horribly fail at this :-) > > I have encountered that one a number of times. All the middleware noise > in Android sometimes give that effect. You've got a typo there: s/middleware/muddleware/ :-) > I'm not sure if the NUMA guy would like rotating scheduler though :-) Hurmph ;-) But yes, the N+1 tasks on a N cpu system is rotten; any static solution gets 2 tasks that run at 50%, any dynamic solution gets the migration overhead issue. So while the dynamic solution would indeed allow each task to (on average) receive N/N+1 time -- a vast improvement over the 50% thing, it doesn't come without down sides.