From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754215Ab2FMQHG (ORCPT ); Wed, 13 Jun 2012 12:07:06 -0400 Received: from casper.infradead.org ([85.118.1.10]:35590 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752534Ab2FMQHE convert rfc822-to-8bit (ORCPT ); Wed, 13 Jun 2012 12:07:04 -0400 Message-ID: <1339603608.8980.55.camel@twins> Subject: Re: [RFC 3/4] ARM: topology: Update cpu_power according to DT information From: Peter Zijlstra To: Vincent Guittot Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linaro-dev@lists.linaro.org, devicetree-discuss@lists.ozlabs.org, linux@arm.linux.org.uk, grant.likely@secretlab.ca, rob.herring@calxeda.com Date: Wed, 13 Jun 2012 18:06:48 +0200 In-Reply-To: References: <1339502524-10265-1-git-send-email-vincent.guittot@linaro.org> <1339502524-10265-4-git-send-email-vincent.guittot@linaro.org> <1339592856.8980.33.camel@twins> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2012-06-13 at 16:54 +0200, Vincent Guittot wrote: > On 13 June 2012 15:07, Peter Zijlstra wrote: > > On Tue, 2012-06-12 at 14:02 +0200, Vincent Guittot wrote: > >> +struct cpu_capacity cpu_capacity[NR_CPUS]; > > > > I know ARM isn't likely to suffer from the 4k cpu issue, but is there a > > reason to use a NR_CPUS array over a per-cpu variable? > > At this stage, we don't know which logical CPU will match which hwid. > During the boot of each CPU, we parse the table to found an efficiency > value for the booting CPU. The whole table is used by one CPU at a > time. Its not so much the usage as the dynamic sizing that I was after. NR_CPUS will always be the max size, whereas per-cpu data will only use the amount of storage required to back the number of cpus present. For this reason we've spend a great deal of effort to remove NR_CPUS sized arrays all over the core (and x86/ia64 arch) code, since distros now build with NR_CPUS=4096 but hardly anybody has that many cpus, so arrays sized that way waste tons of resources. From mboxrd@z Thu Jan 1 00:00:00 1970 From: peterz@infradead.org (Peter Zijlstra) Date: Wed, 13 Jun 2012 18:06:48 +0200 Subject: [RFC 3/4] ARM: topology: Update cpu_power according to DT information In-Reply-To: References: <1339502524-10265-1-git-send-email-vincent.guittot@linaro.org> <1339502524-10265-4-git-send-email-vincent.guittot@linaro.org> <1339592856.8980.33.camel@twins> Message-ID: <1339603608.8980.55.camel@twins> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, 2012-06-13 at 16:54 +0200, Vincent Guittot wrote: > On 13 June 2012 15:07, Peter Zijlstra wrote: > > On Tue, 2012-06-12 at 14:02 +0200, Vincent Guittot wrote: > >> +struct cpu_capacity cpu_capacity[NR_CPUS]; > > > > I know ARM isn't likely to suffer from the 4k cpu issue, but is there a > > reason to use a NR_CPUS array over a per-cpu variable? > > At this stage, we don't know which logical CPU will match which hwid. > During the boot of each CPU, we parse the table to found an efficiency > value for the booting CPU. The whole table is used by one CPU at a > time. Its not so much the usage as the dynamic sizing that I was after. NR_CPUS will always be the max size, whereas per-cpu data will only use the amount of storage required to back the number of cpus present. For this reason we've spend a great deal of effort to remove NR_CPUS sized arrays all over the core (and x86/ia64 arch) code, since distros now build with NR_CPUS=4096 but hardly anybody has that many cpus, so arrays sized that way waste tons of resources.