From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [RFC 3/4] ARM: topology: Update cpu_power according to DT information Date: Wed, 13 Jun 2012 18:06:48 +0200 Message-ID: <1339603608.8980.55.camel@twins> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org 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 List-Id: devicetree@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.