From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754405AbZBRVSS (ORCPT ); Wed, 18 Feb 2009 16:18:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752660AbZBRVR6 (ORCPT ); Wed, 18 Feb 2009 16:17:58 -0500 Received: from ogre.sisk.pl ([217.79.144.158]:44019 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751767AbZBRVR5 convert rfc822-to-8bit (ORCPT ); Wed, 18 Feb 2009 16:17:57 -0500 From: "Rafael J. Wysocki" To: Arve =?iso-8859-1?q?Hj=F8nnev=E5g?= Subject: Re: [RFD] Automatic suspend Date: Wed, 18 Feb 2009 22:17:46 +0100 User-Agent: KMail/1.11.0 (Linux/2.6.29-rc5-tst; KDE/4.2.0; x86_64; ; ) Cc: Alan Stern , "Woodruff, Richard" , Arjan van de Ven , Kyle Moffett , Oliver Neukum , Benjamin Herrenschmidt , pm list , LKML , Pavel Machek , Nigel Cunningham , Matthew Garrett , mark gross , Uli Luckas , Igor Stoppa , Brian Swetland , Len Brown References: <200902180022.00239.rjw@sisk.pl> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 8BIT Content-Disposition: inline Message-Id: <200902182217.48321.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wednesday 18 February 2009, Arve Hjønnevåg wrote: > On Tue, Feb 17, 2009 at 3:21 PM, Rafael J. Wysocki wrote: > > On Tuesday 17 February 2009, Alan Stern wrote: > >> On Tue, 17 Feb 2009, Rafael J. Wysocki wrote: > >> > >> > Phase 1: I agree that system-auto-suspend-on, system-auto-suspend-off would be > >> > useful, but I don't like the wakelocks interface. Do you think there is an > >> > alternative way/mechanism of doing this? > >> > >> I rather like the suggestions Matthew Garrett has been making. They > >> show how to improve the wakelock interface without losing any function. > >> > >> Really, the idea behind wakelocks comes down to the question of how to > >> determine when the system is sufficiently idle to go into auto-suspend. > >> There may be occasions when no task is runnable but userspace knows > >> that the system should not go to sleep because some work will be done > >> in the near future. (Arve's example of a non-empty input buffer is > >> such a case.) How should userspace let the kernel know whether it's > >> okay to suspend at these times? That is the problem userspace > >> wakelocks are meant to solve. > > > > Still, do we really need multiple user space wakelocks (I'd prefer to call them > > sleeplocks)? It seems that one such lock and a user space manager controlling > > it should be sufficient. > > Yes, we could have a user space manager that all userspace wakelocks > go through, but it would have to start before any other processes that > need wakelocks and it would need a blocking ipc mechanism. The > wakelock api that is provided to android applications does all this, > but it is only available to java code. Supporting multiple userspace > wakelocks in the kernel is simpler than adding another userspace > wakelock layer. > > >> Kernel wakelocks are a separate matter. They are more like a form of > >> optimization, preventing the kernel from starting an auto-suspend when > >> some driver knows beforehand that it will return -EBUSY. > > > > I think kernel-side autosuspend (or rather autosleep) should only happen > > after certain subset of devices have been suspended using a per-device > > run-time autosuspend mechanism. > > When the last wakelock is released the task that we woke up to perform > has finished. Why wait to re-enter suspend. I don't really understand this comment. Could you please explain a bit? > >> > Phase 3: Probably explicit control left to open/close. > >> > >> While that's generally a good idea, it's important to recognize that > >> some devices should be runtime-suspended even while they are open. > > > > From the kernel side, yes (and that should be transparent to the user space > > having them open). By the user space, no. > > Allowing user space to suspend input devices while they are still open > is useful. The user-space code that reads from the input devices does > not need to know if the device is suspended or not, and the kernel > cannot auto suspend input devices based on inactivity. Hmm. Why can't it? Rafael