Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752171Ab3FXKKa (ORCPT ); Mon, 24 Jun 2013 06:10:30 -0400 Received: from fw-tnat.cambridge.arm.com ([217.140.96.21]:58714 "EHLO cam-smtp0.cambridge.arm.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751916Ab3FXKK3 (ORCPT ); Mon, 24 Jun 2013 06:10:29 -0400 Date: Mon, 24 Jun 2013 11:07:32 +0100 From: Catalin Marinas To: Benjamin Herrenschmidt Cc: Arjan van de Ven , Morten Rasmussen , David Lang , "len.brown@intel.com" , "alex.shi@intel.com" , "corbet@lwn.net" , "peterz@infradead.org" , Linus Torvalds , "efault@gmx.de" , "linux-kernel@vger.kernel.org" , "linaro-kernel@lists.linaro.org" , "preeti@linux.vnet.ibm.com" , Andrew Morton , "pjt@google.com" , Ingo Molnar Subject: Re: power-efficient scheduling design Message-ID: <20130624100732.GB14982@arm.com> References: <51C07ABC.2080704@linux.intel.com> <51C1D0BB.3040705@linux.intel.com> <20130619170042.GH5460@e103034-lin> <51C1E58D.9000408@linux.intel.com> <20130621085002.GJ5460@e103034-lin> <51C47377.2000208@linux.intel.com> <51C4C6C8.1050008@linux.intel.com> <1372030320.3944.114.camel@pasglop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1372030320.3944.114.camel@pasglop> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1742 Lines: 37 On Mon, Jun 24, 2013 at 12:32:00AM +0100, Benjamin Herrenschmidt wrote: > On Fri, 2013-06-21 at 14:34 -0700, Arjan van de Ven wrote: > > On 6/21/2013 2:23 PM, Catalin Marinas wrote: > > >> > > >> oops sorry I misread your mail (lack of early coffee I suppose) > > >> > > >> I can see your point of having a thing for "did we ask for all the performance > > >> we could ask for" prior to doing a load balance (although, for power efficiency, > > >> if you have two tasks that could run in parallel, it's usually better to > > >> run them in parallel... so likely we should balance anyway) > > > > > > Not necessarily, especially if parallel running implies powering up a > > > full cluster just for one CPU (it depends on the hardware but for > > > example a cluster may not be able to go in deeper sleep states unless > > > all the CPUs in that cluster are idle). > > > > I guess it depends on the system > > Sort-of. We have something similar with threads on ppc. IE, the core can > only really stop if all threads are. From a Linux persepctive it's a > matter of how we define the scope of that 'cluster' Catalin is talking > about. I'm sure you do too. > > Then there is the package, which adds MC etc... I think we can say cluster == package so that we use some common terminology. On a big.little configuration (TC2), we have 3xA7 in one package and 2xA15 in the other. So to efficiently stop an entire package (cluster, multi-core etc.) we need to stop all the CPUs it has. -- Catalin -- 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/