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

Rafael J. Wysocki
2009-12-08T20:51:42Z

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