From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756574AbZBSWW0 (ORCPT ); Thu, 19 Feb 2009 17:22:26 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753694AbZBSWWR (ORCPT ); Thu, 19 Feb 2009 17:22:17 -0500 Received: from ogre.sisk.pl ([217.79.144.158]:51456 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753081AbZBSWWR (ORCPT ); Thu, 19 Feb 2009 17:22:17 -0500 From: "Rafael J. Wysocki" To: Alan Stern Subject: Re: [RFD] Automatic suspend Date: Thu, 19 Feb 2009 23:21:46 +0100 User-Agent: KMail/1.11.0 (Linux/2.6.29-rc5-tst; KDE/4.2.0; x86_64; ; ) Cc: Arve =?iso-8859-1?q?Hj=F8nnev=E5g?= , "Woodruff, Richard" , Arjan van de Ven , Kyle Moffett , Oliver Neukum , Benjamin Herrenschmidt , pm list , LKML , Pavel Machek , Nigel Cunningham , Matthew Garrett , mark gross , Uli Luckas , Igor Stoppa , Brian Swetland , Len Brown 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: <200902192321.47891.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thursday 19 February 2009, Alan Stern wrote: > On Thu, 19 Feb 2009, Rafael J. Wysocki wrote: > > > > > Again, the decision to trigger automatic suspend has to be based on some > > > > well defined criteria and the (in)activity of devices seems to be one of them. > > > > > > I don't know what criteria the system monitor would use. > > > > I don't know either and this is the whole point. They need to be specified > > somehow and I'm not sure if "we suspend if no one is holding a wakelock" is the > > right approach. > > That isn't really a criterion; it's just a mechanism. All it does is > push the problem back one level. Now the question becomes: When is it > appropriate/necessary to hold a wakelock? > > > > It might have to be platform-specific. The Android people seem to have a > > > pretty good idea of what criteria will work for them. > > > > I'd really like to know in what situations Androind is supposed to suspend > > automatically. > > It might be better to ask in what situations Android is _not_ supposed > to sleep automatically. In other words, in what situations is a > wakelock acquired? Since the whole system is only a phone, this > question should have a reasonably well-defined answer. > > > > Inactivity of devices isn't always a good criterion. There might be a > > > background task which wakes up every few seconds to do something as > > > long as the system is awake, thereby keeping some device always active. > > > The activity from this background task shouldn't prevent an auto-sleep. > > > > In fact there are two problems here. First, there may be a task preventing > > some devices from becoming inactive (like syslog). > > Which means that device inactivity isn't always a good indicator for > auto-sleep. (But then there can be different levels of activity: A > disk should always block auto-sleep while it is carrying out I/O, but > it might not block auto-sleep just because it is spinning.) > > > Second, there may be > > a task waiting for something important to happen, such that automatic suspend > > cannot be triggered while it's waiting. In both cases, IMO, the kernel is not > > in a point to decide whether to suspend or not, because the user space knows > > better. > > That's the whole point behind userspace wakelocks! They provide a > mechanism for userspace to tell the kernel when (as far as userspace is > concerned) it is or is not okay to auto-sleep. Still, one can go further and observe that the user space can in fact start automatic suspend by itself whenever it knows it's appropriate ... Thanks, Rafael