From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965384Ab2CPWSi (ORCPT ); Fri, 16 Mar 2012 18:18:38 -0400 Received: from mail-wi0-f170.google.com ([209.85.212.170]:48930 "EHLO mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758270Ab2CPWSg (ORCPT ); Fri, 16 Mar 2012 18:18:36 -0400 From: Christian Lamparter To: "Rafael J. Wysocki" Subject: Re: [PATCH] firmware_class: Move request_firmware_nowait() to workqueues Date: Fri, 16 Mar 2012 23:18:30 +0100 User-Agent: KMail/1.13.7 (Linux/3.3.0-rc6-wl+; KDE/4.7.4; x86_64; ; ) Cc: Stephen Boyd , 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> <4F63A1F6.7070700@codeaurora.org> <201203162245.52281.rjw@sisk.pl> In-Reply-To: <201203162245.52281.rjw@sisk.pl> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-15" Content-Transfer-Encoding: 7bit Message-Id: <201203162318.30770.chunkeey@googlemail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday 16 March 2012 22:45:52 Rafael J. Wysocki wrote: > 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? Just a note: kernel/kmod.c currently defines a workqueue "khelper"... So since we are already "using" kmod's usermodehelper_*, then why not the mess with the workqueue as well? Regards, Chr