Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759469Ab0HDXZi (ORCPT ); Wed, 4 Aug 2010 19:25:38 -0400 Received: from mail.lang.hm ([64.81.33.126]:60586 "EHLO bifrost.lang.hm" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758327Ab0HDXZg (ORCPT ); Wed, 4 Aug 2010 19:25:36 -0400 Date: Wed, 4 Aug 2010 16:23:43 -0700 (PDT) From: david@lang.hm X-X-Sender: dlang@asgard.lang.hm To: =?ISO-8859-15?Q?Arve_Hj=F8nnev=E5g?= 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 Subject: Re: Attempted summary of suspend-blockers LKML thread In-Reply-To: Message-ID: References: <20100801054816.GI2470@linux.vnet.ibm.com> <20100804185520.GA2417@srcf.ucam.org> <201008042251.08266.rjw@sisk.pl> <20100804205654.GA4986@srcf.ucam.org> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: MULTIPART/MIXED; BOUNDARY="680960-1223617944-1280964223=:6545" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4625 Lines: 104 This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --680960-1223617944-1280964223=:6545 Content-Type: TEXT/PLAIN; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8BIT On Wed, 4 Aug 2010, Arve Hj?nnev?g wrote: > 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. in what I'm proposing, if the 'privilaged/trusted" processes are idle long enough the entire system will suspend, and when it wakes up everything will continue to process normally >> 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? I think the timeouts are of such an order of magnatude that the polling can be infrequent enough to not be a significant amount of load, but be faster than any timeout >> 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. So, if I have a bookreader app that is not allowed to get the wakelock, and nothing else is running, the system will suspend immediatly after I click a button to go to the next page? it will not stay awake to give me a chance to read the page at all? how can any application run without wakelock privilages? David Lang --680960-1223617944-1280964223=:6545-- -- 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/