linux-kernel - Re: [PATCH 0/8] Suspend block api (version 7)

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Date:	Tue, 18 May 2010 21:38:04 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Arve Hjønnevåg <arve@...roid.com>
Cc:	Brian Swetland <swetland@...gle.com>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/8] Suspend block api (version 7)

On Tuesday 18 May 2010, Arve Hjønnevåg wrote:
> On Mon, May 17, 2010 at 2:44 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > On Monday 17 May 2010, Brian Swetland wrote:
> >> On Mon, May 17, 2010 at 1:40 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> >> > On Monday 17 May 2010, Arve Hjønnevåg wrote:
> >> >>
> >> >> It should get out of that loop as soon as someone blocks suspend. If
> >> >> someone is constantly aborting suspend without using a suspend blocker
> >> >> it will be very inefficient, but it should still work.
> >> >
> >> > Well, the scenario I have in mind is the following.  Someone wants to check
> >> > the feature and simply writes "opportunistic" to /sys/power/policy and "mem" to
> >> > /sys/power/state without any drivers or apps that use suspend blockers.
> >> >
> >> > How in that case is the system supposed to break out of the suspend-resume loop
> >> > resulting from this?  I don't see right now, because the main blocker is
> >> > inactive, there are no other blockers that can be activated and it is next to
> >> > impossible to write to /sys/power/state again.
> >>
> >> I guess we could set a flag when a suspend blocker is registered and
> >> refuse to enter opportunistic mode if no blockers have ever been
> >> registered.
> >>
> >> It does seem like extra effort to go through to handle a "don't do
> >> that" type scenario (entering into opportunistic suspend without
> >> anything that will prevent it).
> >
> > I agree, but I think it's necessary.  We shouldn't add interfaces that hurt
> > users if not used with care.
> >
> 
> I'm not sure this can be "fixed".

Yes, it can, but perhaps a workaround would be sufficient (see below).

> The user asked that the system to suspend whenever possible, which is what it
> is doing. I don't think disabling opportunistic suspend if no suspend
> blockers have been registered will work. As soon as we register a suspend
> blocker we are back in the same situation.

Not really, because the new suspend blocker is not added by the _framework_ _itself_.

Now, to make it more "user-friendly", we can simply use
queue_delayed_work() with a reasonable delay instead of queue_work() to queue
the suspend work (the delay may be configurable via sysfs).

Thanks,
Rafael
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