Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759486Ab0HDXaV (ORCPT ); Wed, 4 Aug 2010 19:30:21 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:57492 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759439Ab0HDXaR (ORCPT ); Wed, 4 Aug 2010 19:30:17 -0400 Date: Wed, 4 Aug 2010 16:30:13 -0700 From: "Paul E. McKenney" To: david@lang.hm Cc: Arve =?iso-8859-1?B?SGr4bm5lduVn?= , Matthew Garrett , "Rafael J. Wysocki" , 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 Message-ID: <20100804233013.GN24163@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20100801054816.GI2470@linux.vnet.ibm.com> <20100804185520.GA2417@srcf.ucam.org> <201008042251.08266.rjw@sisk.pl> <20100804205654.GA4986@srcf.ucam.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4622 Lines: 100 On Wed, Aug 04, 2010 at 04:23:43PM -0700, david@lang.hm wrote: > 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? Isn't a wakelock held as long as the display is lit, so that the system would continue running as long as the page was visible? Thanx, Paul -- 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/