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

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Message-ID: <20110223093854.GB26065@htj.dyndns.org>
Date:	Wed, 23 Feb 2011 10:38:54 +0100
From:	Tejun Heo <tj@...nel.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
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

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.

Thank you.

-- 
tejun
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