linux-kernel - Re: [PATCH -mm 2/3] Freezer: Use wait queue instead of busy looping (updated)

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Message-ID: <20070802212307.GA521@tv-sign.ru>
Date:	Fri, 3 Aug 2007 01:23:07 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Pavel Machek <pavel@....cz>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [PATCH -mm 2/3] Freezer: Use wait queue instead of busy looping (updated)

On 08/02, Rafael J. Wysocki wrote:
>
> On Thursday, 2 August 2007 20:40, Oleg Nesterov wrote:
> > On 08/02, Rafael J. Wysocki wrote:
> > >
> > > @@ -171,6 +186,10 @@ static int try_to_freeze_tasks(int freez
> > >  
> > >  	end_time = jiffies + TIMEOUT;
> > >  	do {
> > > +		DEFINE_WAIT(wait);
> > > +
> > > +		add_wait_queue(&refrigerator_waitq, &wait);
> > 
> > Hmm. In that case I'd sugest to use prepare_to_wait(). This means that
> > multiple wakeups from refrigerator() won't do unnecessary work,
> 
> I'm not sure what you mean.
> 
> Do you mean that if we are TASK_UNINTERRUPTIBLE, then the first wake up
> should remove us from the queue?

No, not because we are TASK_UNINTERRUPTIBLE, but yes, first wake up will
remove us because DEFINE_WAIT() uses autoremove_wake_function().

Oleg.

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