From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030455AbXDJIPd (ORCPT ); Tue, 10 Apr 2007 04:15:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933103AbXDJIPd (ORCPT ); Tue, 10 Apr 2007 04:15:33 -0400 Received: from hera.kernel.org ([140.211.167.34]:60036 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933106AbXDJIP3 (ORCPT ); Tue, 10 Apr 2007 04:15:29 -0400 From: Len Brown Organization: Intel Open Source Technology Center To: Andi Kleen Subject: Re: CPU offline but power consumption increased? Date: Tue, 10 Apr 2007 04:13:51 -0400 User-Agent: KMail/1.9.5 Cc: "Andika Triwidada" , linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org References: <7e0bae390704062123i2dfaf030icd5a710677bc989a@mail.gmail.com> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200704100413.51637.lenb@kernel.org> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Saturday 07 April 2007 19:38, Andi Kleen wrote: > "Andika Triwidada" writes: > > [cc linux-acpi] > > > Question: is that normal? I thought power consumption will be > > automatically reduced if one core offlined. Known? Yes. What people would expect? No. http://bugzilla.kernel.org/show_bug.cgi?id=5471 > The current cpu offline essentially just runs a special idle loop. > The standard idle loop is even a bit more aggressive on some systems > because it knows about the deeper ACPI sleep modi. > > There are also dependencies between cores because current CPUs > have shared power planes between cores. > > I suppose in the future when a whole socket goes off line one could > implement special code to turn off the CPU further. But it likely > won't work on older hardware. Speaking for all Intel hardware implemented from pre-history until now, deep C-states is the best you can do, and there is no special offline mode to save more power. If you really want to not use a core and the above bug isn't fixed in linux, you can use maxcpus=1 to never bring the other core on-line in the first place, and if the BIOS is implemented properly, the core will be spinning in the deepest available C-state. Of course, it would probably be more interesting to simply leave the core on-line and let it go idle... -Len