linux-kernel - Re: Async resume patch (was: Re: [GIT PULL] PM updates for 2.6.33)

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Message-Id: <200912082152.21910.rjw@sisk.pl>
Date:	Tue, 8 Dec 2009 21:52:21 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Zhang Rui <rui.zhang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: Async resume patch (was: Re: [GIT PULL] PM updates for 2.6.33)

On Tuesday 08 December 2009, Alan Stern wrote:
> On Tue, 8 Dec 2009, Rafael J. Wysocki wrote:
> 
> > > This is a little more awkward because it requires the parent to iterate 
> > > through its children.
> > 
> > I can live with that.
> > 
> > > But it does solve the off-tree dependency  problem for suspends.
> > 
> > That's a plus, but I still think we're trying to create a barrier-alike
> > mechanism using lock.
> > 
> > There's one more possibility to consider, though.  What if we use a completion
> > instead of the flag + wait queue?  It surely is a standard synchronization
> > mechanism and it seems it might work here.
> 
> You're right.  I should have thought of that.  Linus's original
> approach couldn't use a completion because during suspend it needed to
> make one task (the parent) wait for a bunch of others (the children).
> But if you iterate through the children by hand, that objection no
> longer applies.

BTW, is there a good reason why completion_done() doesn't use spin_lock_irqsave
and spin_unlock_irqrestore?  complete() and complete_all() use them, so why not
here?

Rafael
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