From mboxrd@z Thu Jan 1 00:00:00 1970 From: Len Brown Subject: Re: CPU offline but power consumption increased? Date: Tue, 10 Apr 2007 04:13:51 -0400 Message-ID: <200704100413.51637.lenb@kernel.org> References: <7e0bae390704062123i2dfaf030icd5a710677bc989a@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: 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 In-Reply-To: Content-Disposition: inline Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Andi Kleen Cc: Andika Triwidada , linux-kernel@vger.kernel.org, linux-acpi@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