Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759380Ab0HDXPm (ORCPT ); Wed, 4 Aug 2010 19:15:42 -0400 Received: from mail-gy0-f174.google.com ([209.85.160.174]:33991 "EHLO mail-gy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751742Ab0HDXPk convert rfc822-to-8bit (ORCPT ); Wed, 4 Aug 2010 19:15:40 -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 16:15:39 -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: 3523 Lines: 80 2010/8/4 : > On Wed, 4 Aug 2010, Arve Hj?nnev?g wrote: > >> 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. > > and if you don't have a wakelock the same thing will happen. If you expect Not the same thing. If you don't hold a wakelock the entire system will suspend and when it wakes up it continues where it left off. Timeout still have time left before they expire. > the process to take a while you can set a timeout to wake up every 30 > seconds or so and wait again, this would be enough to prevent you from going I don't think polling is an acceptable solution to this problem. You user space code know needs to know what "idle" timeout you have selected so it can choose a faster poll rate. When is it safe to stop polling? > to sleep (or am I misunderstanding how long before you go into suspend > without a wakelock set, see my other e-mail for the full question) > We suspend as soon as no wakelocks are held. There is no delay. -- 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/