linux-kernel - Re: suspend blockers & Android integration

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Date:	Sat, 5 Jun 2010 20:25:11 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Arve Hjønnevåg <arve@...roid.com>
Cc:	Matt Helsley <matthltc@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, tytso@....edu,
	Brian Swetland <swetland@...gle.com>,
	Neil Brown <neilb@...e.de>,
	Alan Stern <stern@...land.harvard.edu>,
	Felipe Balbi <felipe.balbi@...ia.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Florian Mickler <florian@...kler.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	James Bottomley <James.Bottomley@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kevin Hilman <khilman@...prootsystems.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: suspend blockers & Android integration

On Saturday 05 June 2010, Arve Hjønnevåg wrote:
> 2010/6/4 Matt Helsley <matthltc@...ibm.com>:
> > On Fri, Jun 04, 2010 at 05:39:17PM -0700, Arve Hjønnevåg wrote:
> >> On Fri, Jun 4, 2010 at 5:05 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> >> > On Sat, 5 Jun 2010, Rafael J. Wysocki wrote:
> >
> > <snip>
> >
> >>
> >> >     With the cgroup freezer you can "suspend" them right away and
> >> >     just keep the trusted background task(s) alive which allows us to
> >> >     go into deeper idle states instead of letting the crapplications
> >> >     run unconfined until the download finished and the suspend
> >> >     blocker goes away.
> >> >
> >>
> >> Yes this would be better, but I want it in addition to suspend, not
> >> instead of it. It is also unclear if our user-space code could easily
> >> make use of it since our trusted code calls into untrusted code.
> >>
> >
> > Perhaps I'm misunderstanding, but suspend and the cgroup freezer
> > interoperate well today -- you don't have to choose one or the other.
> > If you've discovered otherwise I'd consider it a bug and would like to
> > hear more about it.
> >
> 
> I'm not aware of any bug with combining both, but we cannot use
> suspend at all without suspend blockers in the kernel (since wakeup
> events may be ignored)

The more I think of it, the more it appears to me that the problem of
lost wakeup events can actually be solved without suspend blockers.
I'll send a bunch of patches to address this issue, probably tomorrow.

> and I don't know how we can safely freeze
> cgroups without funneling all potential wakeup events through a
> process that never gets frozen.

If your untrusted apps get called by the trusted ones, they aren't really
untrusted in the first place.

>From what you're saying it follows that you're not really willing to accept
any solution different to your suspend blockers.  Is that really the case?

Rafael
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