From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760309AbXHTPdc (ORCPT ); Mon, 20 Aug 2007 11:33:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756705AbXHTPdZ (ORCPT ); Mon, 20 Aug 2007 11:33:25 -0400 Received: from smtp-101-monday.noc.nerim.net ([62.4.17.101]:1633 "EHLO mallaury.nerim.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756231AbXHTPdY (ORCPT ); Mon, 20 Aug 2007 11:33:24 -0400 Date: Mon, 20 Aug 2007 17:34:50 +0200 From: Jean Delvare To: Oliver Neukum Cc: "Rafael J. Wysocki" , LKML Subject: Re: CONFIG_SUSPEND and power consumption Message-ID: <20070820173450.4ad178a9@hyperion.delvare> In-Reply-To: <200708201211.34698.oliver@neukum.org> References: <20070819153259.2c96b904@hyperion.delvare> <200708192242.43819.rjw@sisk.pl> <20070820120258.7d090cc4@hyperion.delvare> <200708201211.34698.oliver@neukum.org> X-Mailer: Sylpheed-Claws 2.5.5 (GTK+ 2.10.6; x86_64-suse-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 20 Aug 2007 12:11:34 +0200, Oliver Neukum wrote: > Am Montag 20 August 2007 schrieb Jean Delvare: > > If I rmmod "ehci-hcd" then the power consumption is back to 69 W. This > > confirms that this is really USB-related. I have to admit that I did > > not expect an external drive to eat that much power from the system, > > especially when not used. I am told that VIA chips are notoriously bad > > at this kind of things. I'll try the same external drive on an Intel > > system later today. > > > > The last mystery remaining is how USB "activity" can cause my CPU to > > heat. I would expect the south bridge to heat, not the CPU. > > USB, or strictly speaking EHCI, OHCI and UHCI, use DMA. To allow > that the cache coherency logic has to be active. Therefore your CPU > cannot go to C3. Therefore it draws more power. The problem we are > facing in USB is that to get great savings, our coverage has to be perfect. > One device that cannot be autosuspended and we lose most savings. Ah, OK, thanks for the clarification, it explains a lot. I've made some more tests on two Intel boards and another VIA board. The bottom line is that both VIA boards see a bump in power consumption when plugging my USB 2.0 hard disk drive (10 W on one board, 4 W on the other) while none of the Intel boards exhibit any change in power consumption. I wonder if I should blame VIA for eating extra power when the disk is plugged, or thank them for saving power when it's not. Or maybe I am looking at things the wrong way, and I should thank AMD for saving more power in C3 than Intel does? -- Jean Delvare