Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933626Ab0HEPgG (ORCPT ); Thu, 5 Aug 2010 11:36:06 -0400 Received: from ogre.sisk.pl ([217.79.144.158]:41754 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933594Ab0HEPfx convert rfc822-to-8bit (ORCPT ); Thu, 5 Aug 2010 11:35:53 -0400 From: "Rafael J. Wysocki" To: Arve =?iso-8859-1?q?Hj=F8nnev=E5g?= Subject: Re: Attempted summary of suspend-blockers LKML thread Date: Thu, 5 Aug 2010 17:34:06 +0200 User-Agent: KMail/1.13.5 (Linux/2.6.35-rjw+; KDE/4.4.4; x86_64; ; ) Cc: Matthew Garrett , david@lang.hm, "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 References: <20100801054816.GI2470@linux.vnet.ibm.com> <201008050220.51805.rjw@sisk.pl> In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 8BIT Message-Id: <201008051734.06736.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4943 Lines: 106 On Thursday, August 05, 2010, 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? Please refer to the Matthew's response. > >> > 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. You have the stats in struct device and they are available via sysfs. I suppose they are insufficient, but I'd like to know why exactly. > 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. Well, if you need that, you can add a counter of "completed events" into struct dev_pm_info and a function similar to pm_relax() that will update that counter. I don't think anyone will object to that change. > >> 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. Well, until someone actually tries to implement a power manager in user space it's a bit vague. 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/