From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932641Ab2CPVlq (ORCPT ); Fri, 16 Mar 2012 17:41:46 -0400 Received: from ogre.sisk.pl ([217.79.144.158]:49570 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932382Ab2CPVlo (ORCPT ); Fri, 16 Mar 2012 17:41:44 -0400 From: "Rafael J. Wysocki" To: Stephen Boyd Subject: Re: [PATCH] firmware_class: Move request_firmware_nowait() to workqueues Date: Fri, 16 Mar 2012 22:45:52 +0100 User-Agent: KMail/1.13.6 (Linux/3.3.0-rc7+; KDE/4.6.0; x86_64; ; ) Cc: Christian Lamparter , linux-kernel@vger.kernel.org, Linux PM mailing list , "Srivatsa S. Bhat" , alan@lxorguk.ukuu.org.uk, Linus Torvalds , Saravana Kannan , "Greg Kroah-Hartman" , Kay Sievers References: <1331841015-26684-1-git-send-email-sboyd@codeaurora.org> <201203162119.05382.rjw@sisk.pl> <4F63A1F6.7070700@codeaurora.org> In-Reply-To: <4F63A1F6.7070700@codeaurora.org> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-15" Content-Transfer-Encoding: 7bit Message-Id: <201203162245.52281.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday, March 16, 2012, Stephen Boyd wrote: > On 03/16/12 13:19, Rafael J. Wysocki wrote: > > On Friday, March 16, 2012, Stephen Boyd wrote: > >> On 03/15/12 15:31, Rafael J. Wysocki wrote: > >>> On Thursday, March 15, 2012, Stephen Boyd wrote: > >>>> On 03/15/12 13:07, Christian Lamparter wrote: > >>>>> On Thursday, March 15, 2012 08:50:15 PM Stephen Boyd wrote: > >>>>>> Oddly enough a work_struct was already part of the firmware_work > >>>>>> structure but nobody was using it. Instead of creating a new > >>>>>> kthread for each request_firmware_nowait() just schedule the work > >>>>>> on the system workqueue. This should avoid some overhead in > >>>>>> forking new threads when they're not strictly necessary if > >>>>>> workqueues are available. > >>>>>> > >>>>>> Signed-off-by: Stephen Boyd > >>>>>> Cc: Greg Kroah-Hartman > >>>>>> Cc: Kay Sievers > >>>>>> Cc: Rafael J. Wysocki > >>>>>> --- > >>>>>> > >>>>>> I saw this while looking at this problem we're having. > >>>>> Correct me if I'm wrong, but wouldn't that stall all other > >>>>> global workqueue tasks for up to 60 seconds [in worst case]? > >>>>> > >>>>> But I think we can get rid of the firmware_work work struct... > >>>>> > >>>> My understanding is that with concurrency managed workqueues when the > >>>> work item blocks another will be scheduled to run almost immediately. So > >>>> before that change by Tejun workqueues would have been a bad idea > >>>> because it could have blocked up to 60 second but now it should be fine > >>>> because that work item will just be put to sleep and another request > >>>> will run. > >>> Please read the description of system_wq in workqueue.h. > >>> > >>> You should have used either system_long_wq or system_nrt_wq (depending on > >>> what you really need). > >>> > >>> > >> Thanks. I think we can use system_nrt_wq then? Or maybe even the > >> unbounded workqueue system_unbound_wq? > > Hmm. Can you please remind me what the exact role of that work item is? > > > > It loads the device's firmware, but I'm not sure in what situations that's > > supposed to happen. > > > > request_firmware_nowait() is used by code that wants to get the firmware > asynchronously. Callers pass in a callback function which is called once > the firmware is retrieved. The work item will correspond to one call to > request_firmware_nowait(), where the work item will handle the sysfs > entry generation, uevent generation, and wait_for_completion() calls > that _request_firmware() does. > > The work item also executes the callback function the caller passes in > which could do probably anything and could take an arbitrarily long > time. It looks like some drivers even chain request_firmware_nowait() > together by calling request_firmware_nowait() from the callback functions. So it looks like an unbound workqueue would be suitable for that, but perhaps it may even be an ordered one? Rafael