Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755811AbYHOHPb (ORCPT ); Fri, 15 Aug 2008 03:15:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751849AbYHOHPX (ORCPT ); Fri, 15 Aug 2008 03:15:23 -0400 Received: from mx1.suse.de ([195.135.220.2]:54236 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750953AbYHOHPW (ORCPT ); Fri, 15 Aug 2008 03:15:22 -0400 From: Oliver Neukum Organization: Novell To: Alan Stern Subject: Re: [linux-pm] Power management for SCSI Date: Fri, 15 Aug 2008 09:16:23 +0200 User-Agent: KMail/1.9.9 Cc: Pavel Machek , linux-pm@lists.linux-foundation.org, James.Bottomley@hansenpartnership.com, "Linux-pm mailing list" , kernel list , teheo@novell.com References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200808150916.24258.oneukum@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1552 Lines: 35 Am Freitag 15 August 2008 00:25:28 schrieb Alan Stern: > On Thu, 14 Aug 2008, Oliver Neukum wrote: > > > The core problem is that you insist on a rigid bottom-to-top flow of > > autosuspensions. That's good for systems like USB and PCI which > > are trees for PM purposes. It makes no sense for true busses with > > equal members on the bus. > > My framework is tree-oriented because it's based on the driver model, > which uses a tree of devices. Which uses a tree because PCI and USB are. > Even on a true bus, the members can't be entirely equal -- one of them > has to be closer to the CPU than the others are. If that one member is > in a low-power state then the CPU can't communicate with anything on > the bus, unlike when one of the other members is in a low-power state. Yes, that means under some circumstances you cannot suspend the member closest to the CPU, but under others you can. In a tree this question is very simply answered, on a bus you will actually need to compute whether you need the connection to the bus. It is true that you won't need the bus if all other members on the bus have been suspended, but that's not very good because physically spinning down and up a disk is a very expensive operation, while suspending a host adapter can be trivial. Regards Oliver -- 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/