From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760022AbXLOAMc (ORCPT ); Fri, 14 Dec 2007 19:12:32 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753006AbXLOAMY (ORCPT ); Fri, 14 Dec 2007 19:12:24 -0500 Received: from [194.117.236.238] ([194.117.236.238]:59311 "EHLO heracles.linux360.ro" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752754AbXLOAMX (ORCPT ); Fri, 14 Dec 2007 19:12:23 -0500 Date: Sat, 15 Dec 2007 02:10:32 +0200 From: Eduard-Gabriel Munteanu To: Chuck Ebbert Cc: Andi Kleen , LKML Subject: Re: [PATCH] Option to disable AMD C1E (allows dynticks to work) Message-ID: <20071215021032.252455be@linux360.ro> In-Reply-To: <47630521.4060505@redhat.com> References: <20071214004442.5f9eba88@linux360.ro> <20071214143941.2c7dcfb4@linux360.ro> <20071214101720.GA10981@one.firstfloor.org> <47630521.4060505@redhat.com> X-Mailer: Claws Mail 3.0.2 (GTK+ 2.10.14; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 14 Dec 2007 17:35:13 -0500 Chuck Ebbert wrote: > On 12/14/2007 05:17 AM, Andi Kleen wrote: > >> so do whatever is necessary to enable dynticks. > > > > dynticks' main purpose is to save power, but C1e saves more power. > > Disabling C1e for dynticks would be a fairly useless default > > trade off. > > > > What about machines where the BIOS has disabled C1e on CPU 0 but > left it enabled on CPU 1 ?? Do you mean Linux should enable C1E on CPU 0 if it's detected on CPU 1? C3 + dynticks make up a better power saver than simply C1E, as far as I know. Higher C-states should be enabled on such CPUs, as AMD docs say firmware should either enable C1E or C2 & C3 (it must provide one of these mutually exclusive options). I take having C1E on the second CPU but not the first as an attempt on BIOS's part to provide higher C-states instead of the former. How broken is it, really? But maybe someone with access to such hardware can tell us what happens: does he get C2/C3 power states under such circumstances?