From mboxrd@z Thu Jan 1 00:00:00 1970 From: peterz@infradead.org (Peter Zijlstra) Date: Tue, 11 Mar 2014 14:17:19 +0100 Subject: [RFC 0/6] rework sched_domain topology description In-Reply-To: <531B0FDA.2040302@arm.com> References: <1394003906-11630-1-git-send-email-vincent.guittot@linaro.org> <5317B092.7070805@arm.com> <53186A8A.9060406@arm.com> <531B0FDA.2040302@arm.com> Message-ID: <20140311131719.GY9987@twins.programming.kicks-ass.net> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Sat, Mar 08, 2014 at 12:40:58PM +0000, Dietmar Eggemann wrote: > > > >I don't have a strong opinion about using or not a cpu argument for > >setting the flags of a level (it was part of the initial proposal > >before we start to completely rework the build of sched_domain) > >Nevertheless, I see one potential concern that you can have completely > >different flags configuration of the same sd level of 2 cpus. > > Could you elaborate a little bit further regarding the last sentence? Do you > think that those completely different flags configuration would make it > impossible, that the load-balance code could work at all at this sd? So a problem with such an interfaces is that is makes it far too easy to generate completely broken domains. You can, for two cpus in the same domain provide, different flags; such a configuration doesn't make any sense at all. Now I see why people would like to have this; but unless we can make it robust I'd be very hesitant to go this route. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753178AbaCKNR4 (ORCPT ); Tue, 11 Mar 2014 09:17:56 -0400 Received: from merlin.infradead.org ([205.233.59.134]:53542 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751082AbaCKNRz (ORCPT ); Tue, 11 Mar 2014 09:17:55 -0400 Date: Tue, 11 Mar 2014 14:17:19 +0100 From: Peter Zijlstra To: Dietmar Eggemann Cc: Vincent Guittot , "mingo@kernel.org" , "linux-kernel@vger.kernel.org" , "tony.luck@intel.com" , "fenghua.yu@intel.com" , "schwidefsky@de.ibm.com" , "james.hogan@imgtec.com" , "cmetcalf@tilera.com" , "benh@kernel.crashing.org" , "linux@arm.linux.org.uk" , "linux-arm-kernel@lists.infradead.org" , "preeti@linux.vnet.ibm.com" , "linaro-kernel@lists.linaro.org" Subject: Re: [RFC 0/6] rework sched_domain topology description Message-ID: <20140311131719.GY9987@twins.programming.kicks-ass.net> References: <1394003906-11630-1-git-send-email-vincent.guittot@linaro.org> <5317B092.7070805@arm.com> <53186A8A.9060406@arm.com> <531B0FDA.2040302@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <531B0FDA.2040302@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 Sat, Mar 08, 2014 at 12:40:58PM +0000, Dietmar Eggemann wrote: > > > >I don't have a strong opinion about using or not a cpu argument for > >setting the flags of a level (it was part of the initial proposal > >before we start to completely rework the build of sched_domain) > >Nevertheless, I see one potential concern that you can have completely > >different flags configuration of the same sd level of 2 cpus. > > Could you elaborate a little bit further regarding the last sentence? Do you > think that those completely different flags configuration would make it > impossible, that the load-balance code could work at all at this sd? So a problem with such an interfaces is that is makes it far too easy to generate completely broken domains. You can, for two cpus in the same domain provide, different flags; such a configuration doesn't make any sense at all. Now I see why people would like to have this; but unless we can make it robust I'd be very hesitant to go this route.