From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755802Ab2ATXqI (ORCPT ); Fri, 20 Jan 2012 18:46:08 -0500 Received: from ogre.sisk.pl ([217.79.144.158]:43936 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753663Ab2ATXqE (ORCPT ); Fri, 20 Jan 2012 18:46:04 -0500 From: "Rafael J. Wysocki" To: paulmck@linux.vnet.ibm.com Subject: Re: [PATCH 3/3] serial: 8250: Add a wakeup_capable module param Date: Sat, 21 Jan 2012 00:49:35 +0100 User-Agent: KMail/1.13.6 (Linux/3.2.0+; KDE/4.6.0; x86_64; ; ) Cc: Simon Glass , Alan Cox , LKML , "Greg Kroah-Hartman" , linux-serial@vger.kernel.org References: <1326826563-32215-1-git-send-email-sjg@chromium.org> <201201200103.34296.rjw@sisk.pl> <20120120061214.GA2551@linux.vnet.ibm.com> In-Reply-To: <20120120061214.GA2551@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201201210049.35254.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday, January 20, 2012, Paul E. McKenney wrote: > On Fri, Jan 20, 2012 at 01:03:34AM +0100, Rafael J. Wysocki wrote: > > On Thursday, January 19, 2012, Paul E. McKenney wrote: > > > On Thu, Jan 19, 2012 at 01:02:58AM +0100, Rafael J. Wysocki wrote: > > > > On Wednesday, January 18, 2012, Paul E. McKenney wrote: > > > > > On Wed, Jan 18, 2012 at 02:15:59PM -0800, Simon Glass wrote: > > [...] > > > > Yes, you can, but then I'd say it's not necessary for user space to > > > > be able to carry that out in a tight loop. So, it seems, alternatively, > > > > we could make that loop a bit less tight, e.g. by adding an arbitrary > > > > sleep to the user space interface for the "disable" case. > > > > > > Good point, that would work just as well and be simpler. > > > > Thanks for the confirmation! :-) > > > > By the way, I wonder, would it help to add synchronize_rcu() to > > wakeup_source_add() too? Then, even if device_wakeup_enable() and > > device_wakeup_disable() are executed in a tight loop for the same > > device, the list_add/list_del operations will always happen in > > different RCU cycles (or at least it seems so). > > I cannot immediately see how adding a synchronize_rcu() to > wakeup_source_add() would help anything. You only need to wait for a > grace period on removal, not (normally) on addition. The single grace > period during removal will catch up all other asynchronous RCU grace > period requests on that CPU. > > Or am I missing your point? Well, I was thinking about the failure scenario you mentioned where executing enable/disable in a tight loop might exhaust system memory (if I understood it correctly). Thanks, Rafael