From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753258Ab0EGAKR (ORCPT ); Thu, 6 May 2010 20:10:17 -0400 Received: from mail-vw0-f46.google.com ([209.85.212.46]:55510 "EHLO mail-vw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752785Ab0EGAKN convert rfc822-to-8bit (ORCPT ); Thu, 6 May 2010 20:10:13 -0400 MIME-Version: 1.0 In-Reply-To: <20100506170420.GB30928@atomide.com> References: <20100505202826.GB7450@linux.intel.com> <20100505234755.GI29604@atomide.com> <20100506000552.GJ29604@atomide.com> <20100506170420.GB30928@atomide.com> Date: Thu, 6 May 2010 17:10:11 -0700 Message-ID: Subject: Re: [linux-pm] [PATCH 1/8] PM: Add suspend block api. From: =?ISO-8859-1?Q?Arve_Hj=F8nnev=E5g?= To: Tony Lindgren Cc: Brian Swetland , Alan Stern , mark gross , markgross@thegnar.org, Len Brown , linux-doc@vger.kernel.org, Kernel development list , Jesse Barnes , Oleg Nesterov , Tejun Heo , Linux-pm mailing list , Wu Fengguang , Andrew Morton Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2010/5/6 Tony Lindgren : > * Arve Hjønnevåg [100505 21:11]: >> On Wed, May 5, 2010 at 5:05 PM, Tony Lindgren wrote: >> > * Brian Swetland [100505 16:51]: >> >> On Wed, May 5, 2010 at 4:47 PM, Tony Lindgren wrote: >> >> > * Brian Swetland [100505 14:34]: >> >> >> On Wed, May 5, 2010 at 2:12 PM, Alan Stern wrote: >> >> >> >> >> >> >> >> Oh, like tell the modem that user mode has handled the ring event and >> >> >> >> its ok to un-block? >> >> >> > >> >> >> > No, that's not how it works.  It would go like this: >> >> >> > >> >> >> >        The modem IRQ handler queues its event to the input subsystem. >> >> >> >        As it does so the input subsystem enables a suspend blocker, >> >> >> >        causing the system to stay awake after the IRQ is done. >> >> > >> >> > How about instead the modem driver fails to suspend until it's done? >> >> > >> >> > Each driver could have a suspend_policy sysfs entry with options such >> >> > as [ forced | safe ]. The default would be forced. Forced would >> >> > be the current behaviour, while safe would refuse suspend until the >> >> > driver is done processing. >> >> > >> >> >> >        The user program enables its own suspend blocker before reading >> >> >> >        the input queue.  When the queue is empty, the input subsystem >> >> >> >        releases its suspend blocker. >> >> > >> >> > And also the input layer could refuse to suspend until it's done. >> >> > >> >> >> >        When the user program finishes processing the event, it >> >> >> >        releases its suspend blocker.  Now the system can go back to >> >> >> >        sleep. >> >> > >> >> > And here the user space just tries to suspend again when it's done? >> >> > It's not like you're trying to suspend all the time, so it should be >> >> > OK to retry a few times. >> >> >> >> We actually are trying to suspend all the time -- that's our basic >> >> model -- suspend whenever we can when something doesn't prevent it. >> > >> > Maybe that state could be kept in some userspace suspend policy manager? >> > >> >> >> > At no point does the user program have to communicate anything to the >> >> >> > modem driver, and at no point does it have to do anything out of the >> >> >> > ordinary except to enable and disable a suspend blocker. >> >> >> >> >> >> Exactly -- and you can use the same style of overlapping suspend >> >> >> blockers with other drivers than input, if the input interface is not >> >> >> suitable for the particular interaction. >> >> > >> >> > Would the suspend blockers still be needed somewhere in the example >> >> > above? >> >> >> >> How often would we retry suspending? >> > >> > Well based on some timer, the same way the screen blanks? Or five >> > seconds of no audio play? So if the suspend fails, then reset whatever >> > userspace suspend policy timers. >> > >> >> If we fail to suspend, don't we have to resume all the drivers that >> >> suspended before the one that failed?  (Maybe I'm mistaken here) >> > >> > Sure, but I guess that should be a rare event that only happens when >> > you try to suspend and something interrupts the suspend. >> > >> >> This is not a rare event. For example, the matrix keypad driver blocks >> suspend when a key is down so it can scan the matrix. > > Sure, but how many times per day are you suspending? > How many times we successfully suspend is irrelevant here. If the driver blocks suspend the number of suspend attempts depend on your poll frequency. >> >> With the suspend block model we know the moment we're capable of >> >> suspending and then can suspend at that moment.  Continually trying to >> >> suspend seems like it'd be inefficient power-wise (we're going to be >> >> doing a lot more work as we try to suspend over and over, or we're >> >> going to retry after a timeout and spend extra time not suspended). >> >> >> >> We can often spend minutes (possibly many) at a time preventing >> >> suspend when the system is doing work that would be interrupted by a >> >> full suspend. >> > >> > Maybe you a userspace suspend policy manager would do the trick if >> > it knows when the screen is blanked and no audio has been played for >> > five seconds etc? >> > >> >> If user space has to initiate every suspend attempt, then you are >> forcing it to poll whenever a driver needs to block suspend. > > Hmm I don't follow you. If the userspace policy daemon timer times > out, the device suspends. If the device does not suspend because of > a blocking driver, then the timers get reset and you try again based > on some event such as when the screen blanks. > This retry is what I call polling. You have to keep retrying until you succeed. Also, using the screen blank timeout for this polling is not a good idea. You do not want to toggle the screen off and on with with every suspend attempt. -- Arve Hjønnevåg