linux-kernel - Re: [PATCH 2/2] firmware_class: Move request_firmware

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Date:	Wed, 28 Mar 2012 00:55:06 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Tejun Heo <tj@...nel.org>, Stephen Boyd <sboyd@...eaurora.org>
Cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Saravana Kannan <skannan@...eaurora.org>,
	Kay Sievers <kay.sievers@...y.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Christian Lamparter <chunkeey@...glemail.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	alan@...rguk.ukuu.org.uk,
	Linux PM mailing list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 2/2] firmware_class: Move request_firmware_nowait() to workqueues

On Wednesday, March 28, 2012, Tejun Heo wrote:
> On Wed, Mar 28, 2012 at 12:21:27AM +0200, Rafael J. Wysocki wrote:
> > On Wednesday, March 28, 2012, Tejun Heo wrote:
> > > On Tue, Mar 27, 2012 at 02:28:30PM -0700, 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() call just schedule the
> > > > work on the long system workqueue. This should avoid some overhead
> > > > in forking new threads when they're not strictly necessary.
> > > > 
> > > > Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
> > > > ---
> > > > 
> > > > Is it better to use alloc_workqueue() and not put these on the system
> > > > long workqueue?
> > > 
> > > No, just use schedule_work() unless there are specific requirements
> > > which can't be fulfilled that way (e.g. it's on memory allocation
> > > path, may consume large amount of cpu cycles, ...)
> > 
> > It may wait quite long.
> 
> That shouldn't matter.  system_long_wq's name is a bit misleading at
> this point.  The only reason it's used currently is to avoid cyclic
> dependency involving flush_workqueue(), which calls for clearer
> solution anyway.  So, yeap, using system_wq should be fine here.

Good, thanks for the explanation.

Stephen, care to respin?

Rafael
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