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

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Message-ID: <20120327224837.GC22371@google.com>
Date:	Tue, 27 Mar 2012 15:48:37 -0700
From:	Tejun Heo <tj@...nel.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Stephen Boyd <sboyd@...eaurora.org>, 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 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.

Thank you.

-- 
tejun
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