linux-kernel - Re: [update] Re: [PATCH] PM: Make it possible to avoid wakeup events from being lost

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Date:	Wed, 30 Jun 2010 15:58:36 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	linux-pm@...ts.linux-foundation.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Neil Brown <neilb@...e.de>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	mark gross <640e9920@...il.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Florian Mickler <florian@...kler.org>,
	<linux-pci@...r.kernel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: [update] Re: [PATCH] PM: Make it possible to avoid wakeup events
 from being lost

On Wed, 30 Jun 2010, Rafael J. Wysocki wrote:

> > Since there's no longer any way to cancel a call to pm_wakeup_event()  
> > or close the "no suspend" period early, there is no need to use
> > dynamically-allocated delayed_work structures.  You can make do with a
> > single static timer; always keep it set to expire at the latest time
> > passed to pm_wakeup_event().
> 
> The decremenations of events_in_progress wouldn't be balanced with
> incrementations this way.  Or do you have any clever way of dealing with
> that in mind?

Keep track of the current expiration time in a static variable called
wakeup_timeout, and use 0 to indicate there is no timeout.

In pm_wakeup_event() (everything protected by the spinlock):

	unsigned long new_timeout = jiffies + msecs_to_jiffies(msecs);
	if (new_timeout == 0)
		new_timeout = 1;

	++event_count;
	if (!wakeup_timeout || time_after(new_timeout, wakeup_timeout)) {
		if (!wakeup_timeout)
			++events_in_progress;
		wakeup_timeout = new_timeout;
		mod_timer(&wakeup_timer, wakeup_timeout);
	}

In the timer routine:

	if (wakeup_timeout && time_before_eq(wakeup_timeout, jiffies)) {
		--events_in_progres;
		wakeup_timeout = 0;
	}

Alan Stern

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