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

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Date:	Thu, 15 Mar 2012 23:31:14 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Christian Lamparter <chunkeey@...glemail.com>,
	linux-kernel@...r.kernel.org,
	Linux PM mailing list <linux-pm@...r.kernel.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	alan@...rguk.ukuu.org.uk,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Saravana Kannan <skannan@...eaurora.org>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	Kay Sievers <kay.sievers@...y.org>
Subject: Re: [PATCH] firmware_class: Move request_firmware_nowait() to workqueues

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 <sboyd@...eaurora.org>
> >> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> >> Cc: Kay Sievers <kay.sievers@...y.org>
> >> Cc: Rafael J. Wysocki <rjw@...k.pl>
> >> ---
> >>
> >> 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,
Rafael
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