linux-kernel - Re: [RFD] Automatic suspend

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Message-Id: <200902272154.03539.rjw@sisk.pl>
Date:	Fri, 27 Feb 2009 21:54:01 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	Pavel Machek <pavel@....cz>, "Arve Hj?nnev?g" <arve@...roid.com>,
	Alan Stern <stern@...land.harvard.edu>,
	"Woodruff, Richard" <r-woodruff2@...com>,
	Arjan van de Ven <arjan@...radead.org>,
	Kyle Moffett <kyle@...fetthome.net>,
	Oliver Neukum <oliver@...kum.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	mark gross <mgross@...ux.intel.com>,
	Uli Luckas <u.luckas@...d.de>,
	Igor Stoppa <igor.stoppa@...ia.com>,
	Brian Swetland <swetland@...gle.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [RFD] Automatic suspend

On Friday 27 February 2009, Matthew Garrett wrote:
> On Fri, Feb 27, 2009 at 03:22:39PM +0100, Rafael J. Wysocki wrote:
> > On Friday 27 February 2009, Pavel Machek wrote:
> > > Wakelocks done right are single atomic_t... and if you set it to 0,
> > > you just unblock "sleeper" thread or something. Zero polling and very
> > > simple...
> > 
> > Except that you have to check all of the wakelocks periodically in a loop =>
> > polling.  So?
> 
> Why do you need to check them? If you're taking this approach you just 
> have something like:
> 
> suspend_unblock() {
> 	if (atomc_dec_and_test(&suspend_lock))
> 		suspend();
> }
> 
> and then check that the lock count is still 0 after device_suspend(). 
> There's no need to poll.

I was talking about wakelocks as originally proposed.

Using a refcount along with per-driver and per-process flags (probably two
refcounts would be more efficient in fact) is the latest idea and I agree it
wouldn't require polling.  However, if you refer to that, please don't use the
name "wakelock". :-)

Thanks,
Rafael
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