linux-kernel - Re: Boot time regression in 2.6.38 after initial wq merge

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Date:	Wed, 23 Feb 2011 02:22:58 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	"pantherchen@...sanet.de" <pantherchen@...sanet.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Boot time regression in 2.6.38 after initial wq merge

On Wed, Feb 23, 2011 at 10:38:54AM +0100, Tejun Heo wrote:
> Hello,
> 
> On Tue, Feb 22, 2011 at 09:20:42PM -0800, Dmitry Torokhov wrote:
> > On Tue, Feb 22, 2011 at 09:14:46PM +0100, pantherchen@...sanet.de wrote:
> > > On 02/22/2011 08:52 PM, Dmitry Torokhov wrote:
> > > >Ewww... tty/ldisc...
> > > >
> > > >Does it help if you change drivers/input/serio/serio.c::serio_queue_event()
> > > >from calling
> > > >
> > > >	schedule_work(&serio_event_work);
> > > >
> > > >to call
> > > >
> > > >	queue_work(system_long_wq,&serio_event_work);
> > > >
> > > >?
> > > 
> > > Yes, that works: http://img.xrmb2.net/images/499337.png
> > > 
> > 
> > Great!
> > 
> > OK, so below is properly formatted patch. I am going to send it upstream
> > unless somebody objects.
> 
> Ah, okay, thanks a lot for tracking this down, Dmitry.  Didn't expect
> flush_scheduled_work() to bite back this way.  :-)
> 
> > Input: serio/gameport - use 'long' system workqueue
> > 
> > From: Dmitry Torokhov <dmitry.torokhov@...il.com>
> > 
> > Commit 8ee294cd9def0004887da7f44b80563493b0a097 converted serio
> > subsystem event handling from using a dedicated thread to using
> > common workqueue. Unfortunately, this regressed our boot times,
> > due to the fact that serio jobs take long time to execute. While
> > the new concurrency managed workqueue code manages long-playing
> > works just fine and schedules additional workers as needed, such
> > works wreck havoc among remaining users of flush_scheduled_work().
> > 
> > To solve this problem let's move serio/gameport works from system_wq
> > to system_long_wq which nobody tries to flush.
> > 
> > Reported-and-tested-by: Hernando Torque <pantherchen@...sanet.de>
> > Signed-off-by: Dmitry Torokhov <dtor@...l.ru>
> 
> Acked-by: Tejun Heo <tj@...nel.org>
> 
> Most flush_scheduled_work() users are already gone and once all of
> them are gone, system_long_wq can be removed without causing any
> difference.

Right. When you are ready to remove system_long_wq simply revert this
path and all should be set.

Thanks.

-- 
Dmitry
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