Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758411Ab0HDWvh (ORCPT ); Wed, 4 Aug 2010 18:51:37 -0400 Received: from mail-gw0-f46.google.com ([74.125.83.46]:36707 "EHLO mail-gw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756404Ab0HDWvf convert rfc822-to-8bit (ORCPT ); Wed, 4 Aug 2010 18:51:35 -0400 MIME-Version: 1.0 In-Reply-To: References: <20100801054816.GI2470@linux.vnet.ibm.com> <20100804185520.GA2417@srcf.ucam.org> <201008042251.08266.rjw@sisk.pl> <20100804205654.GA4986@srcf.ucam.org> Date: Wed, 4 Aug 2010 15:51:34 -0700 Message-ID: Subject: Re: Attempted summary of suspend-blockers LKML thread From: =?ISO-8859-1?Q?Arve_Hj=F8nnev=E5g?= To: david@lang.hm Cc: Matthew Garrett , "Rafael J. Wysocki" , "Paul E. McKenney" , Arjan van de Ven , linux-pm@lists.linux-foundation.org, linux-kernel@vger.kernel.org, pavel@ucw.cz, florian@mickler.org, stern@rowland.harvard.edu, swetland@google.com, peterz@infradead.org, tglx@linutronix.de, alan@lxorguk.ukuu.org.uk Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2498 Lines: 53 On Wed, Aug 4, 2010 at 3:31 PM, wrote: > On Wed, 4 Aug 2010, Matthew Garrett wrote: > >> On Wed, Aug 04, 2010 at 10:51:07PM +0200, Rafael J. Wysocki wrote: >>> >>> On Wednesday, August 04, 2010, Matthew Garrett wrote: >>>> >>>> No! And that's precisely the issue. Android's existing behaviour could >>>> be entirely implemented in the form of binary that manually triggers >>>> suspend when (a) the screen is off and (b) no userspace applications >>>> have indicated that the system shouldn't sleep, except for the wakeup >>>> event race. Imagine the following: >>>> >>>> 1) The policy timeout is about to expire. No applications are holding >>>> wakelocks. The system will suspend providing nothing takes a wakelock. >>>> 2) A network packet arrives indicating an incoming SIP call >>>> 3) The VOIP application takes a wakelock and prevents the phone from >>>> suspending while the call is in progress >>>> >>>> What stops the system going to sleep between (2) and (3)? cgroups don't, >>>> because the voip app is an otherwise untrusted application that you've >>>> just told the scheduler to ignore. >>> >>> I _think_ you can use the just-merged /sys/power/wakeup_count mechanism >>> to >>> avoid the race (if pm_wakeup_event() is called at 2)). >> >> Yes, I think that solves the problem. The only question then is whether >> it's preferable to use cgroups or suspend fully, which is pretty much up >> to the implementation. In other words, is there a reason we're still >> having this conversation? :) It'd be good to have some feedback from >> Google as to whether this satisfies their functional requirements. > > the proposal that I nade was not to use cgroups to freeze some processes and > not others, but to use cgroups to decide to ignore some processes when > deciding if the system is idle, stop everything or nothing. cgroups are just > a way of easily grouping processes (and their children) into different > groups. > That does not avoid the dependency problem. A process may be waiting on a resource that a process you ignore owns. I you ignore the process that owns the resource and enter idle when it is ready to run (or waiting on a timer), you are still effectively blocking the other process. -- Arve Hj?nnev?g -- 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/