Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758823Ab0HED7m (ORCPT ); Wed, 4 Aug 2010 23:59:42 -0400 Received: from e4.ny.us.ibm.com ([32.97.182.144]:49836 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758765Ab0HED7j (ORCPT ); Wed, 4 Aug 2010 23:59:39 -0400 Date: Wed, 4 Aug 2010 20:59:34 -0700 From: "Paul E. McKenney" To: Arve =?iso-8859-1?B?SGr4bm5lduVn?= Cc: "Rafael J. Wysocki" , Matthew Garrett , david@lang.hm, 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: <20100805035934.GA2491@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20100801054816.GI2470@linux.vnet.ibm.com> <20100804205654.GA4986@srcf.ucam.org> <201008050220.51805.rjw@sisk.pl> 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: 5264 Lines: 116 On Wed, Aug 04, 2010 at 06:02:28PM -0700, Arve Hj?nnev?g wrote: > 2010/8/4 Rafael J. Wysocki : > > On Thursday, August 05, 2010, Arve Hj?nnev?g wrote: > >> On Wed, Aug 4, 2010 at 1:56 PM, 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 > >> > >> How? By passing a timeout to pm_wakeup_event when the network driver > >> gets the packet or by passing 0. If you pass a timeout it is the same > >> as using a wakelock with a timeout and should work (assuming the > >> timeout you picked is long enough). If you don't pass a timeout it > >> does not work, since the packet may not be visible to user-space yet. > > > > Alternatively, pm_stay_awake() / pm_relax() can be used. > > Which makes the driver and/or network stack changes identical to using > wakelocks, right? Arve, you say that like it is a bad thing. ;-) Seriously, the hope is that Rafael's implementation is useful to other projects in addition to Android. And, all else being equal, the more people who need a given facility, the more likely that facility is to make it to mainline, right? And yes, I see you call out some additional things that Android needs, but hopefully this gap can be closed one way or another. Thanx, Paul > >> > 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 > >> > >> I have seen no proposed way to use cgroups that will work. If you > >> leave some processes running while other processes are frozen you run > >> into problems when a frozen process holds a resource that a running > >> process needs. > >> > >> > >> > having this conversation? :) It'd be good to have some feedback from > >> > Google as to whether this satisfies their functional requirements. > >> > > >> > >> That is "this"? The merged code? If so, no it does not satisfy our > >> requirements. The in kernel api, while offering similar functionality > >> to the wakelock interface, does not use any handles which makes it > >> impossible to get reasonable stats (You don't know which pm_stay_awake > >> request pm_relax is reverting). > > > > Why is that a problem (out of curiosity)? > > > > Not having stats or not knowing what pm_relax is undoing? We need > stats to be able to debug the system. If the system does not suspend > at all or is awake for too long, the wakelock stats tells us which > component is at fault. Since pm_stay_awake and pm_relax does not > operate on a handle, you cannot determine how long it prevented > suspend for. > > >> The proposed in user-space interface > >> of calling into every process that receives wakeup events before every > >> suspend call > > > > Well, ?you don't really need to do that. > > > > Only if the driver blocks suspend until user-space has read the event. > This means that for android to work we need to block suspend when > input events are not processed, but a system using your scheme needs a > pm_wakeup_event call when the input event is queued. How to you switch > between them? Do we add separate ioctls in the input device to enable > each scheme? If someone has a single threaded user space power manager > that also reads input event it will deadlock if you block suspend > until it reads the input events since you block when reading the wake > count. > > >> is also not compatible with existing apps. > > > > Thanks, > > Rafael > > -- > > 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/ > > > > > > -- > 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/