Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755263AbYCNEPT (ORCPT ); Fri, 14 Mar 2008 00:15:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750889AbYCNEPH (ORCPT ); Fri, 14 Mar 2008 00:15:07 -0400 Received: from hera.kernel.org ([140.211.167.34]:42346 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750779AbYCNEPF (ORCPT ); Fri, 14 Mar 2008 00:15:05 -0400 From: Len Brown Organization: Intel Open Source Technology Center To: Andi Kleen Subject: Re: [linux-pm] [PATCH] cpuidle: avoid singing capacitors Date: Fri, 14 Mar 2008 00:13:58 -0400 User-Agent: KMail/1.9.9 Cc: Pavel Machek , linux-pm@lists.linux-foundation.org, Pierre Ossman , LKML , Adam Belay , Lee Revell References: <20080313081048.GB19808@elf.ucw.cz> <20080313104217.GH2522@one.firstfloor.org> In-Reply-To: <20080313104217.GH2522@one.firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200803140013.59146.lenb@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1479 Lines: 36 On Thursday 13 March 2008, Andi Kleen wrote: > On Thu, Mar 13, 2008 at 09:10:48AM +0100, Pavel Machek wrote: > > Hi! > > > > > > > USB keeps processor out of C3 in many cases. > > > > > > > > I figured that was the case. But I did not see any difference in powertop. > > > > > > Modern Intel mobile processors have a feature called "C2 popup" > > > that allows the processor to retire DMA from C3 without > > > breaking into C0. Instead the processor pops up to C2 > > > where the cache snoop can allow the DMA to retire -- > > > then it returns to C3, all transparent to software. > > > > Does that mean we should go to C3 on modern intels, even with > > busmaster going on, so that cpu can keep going C2..C3..C2 as needed? That decision has already been made for us. BM_STS has been made a no-op on recent processors. It reports bus activity only for a small sub-set of south-bridge devices. Otherwise it tells us there is none and that we should proceed into C3. > C3 is still more expensive power wise to enter, so entering C3 just > to let it immediately go back to C2 for bus mastering would be likely > still a loss over staying at C2. The newer the processor, the less exposed we area to this scenario. cheers, -Len -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/