From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760028AbXHTS6r (ORCPT ); Mon, 20 Aug 2007 14:58:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753182AbXHTS6i (ORCPT ); Mon, 20 Aug 2007 14:58:38 -0400 Received: from ogre.sisk.pl ([217.79.144.158]:40481 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752886AbXHTS6i (ORCPT ); Mon, 20 Aug 2007 14:58:38 -0400 From: "Rafael J. Wysocki" To: Pavel Machek Subject: Re: CONFIG_SUSPEND and power consumption Date: Mon, 20 Aug 2007 21:08:35 +0200 User-Agent: KMail/1.9.5 Cc: Oliver Neukum , Jean Delvare , LKML References: <20070819153259.2c96b904@hyperion.delvare> <200708201211.34698.oliver@neukum.org> <20070820172907.GC3975@ucw.cz> In-Reply-To: <20070820172907.GC3975@ucw.cz> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200708202108.35674.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Monday, 20 August 2007 19:29, Pavel Machek wrote: > Hi! > > > > 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. > > Ok.. but CONFIG_USB_SUSPEND should not really have anything to do with > CONFIG_SUSPEND (= s2ram). Perhaps it should depend on CONFIG_PM > instead? CONFIG_USB_SUSPEND doesn't depend on CONFIG_SUSPEND. Greetings, Rafael