linux-kernel - Re: suspend blockers & Android integration

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Message-ID: <1275646439.27810.39540.camel@twins>
Date:	Fri, 04 Jun 2010 12:13:59 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Ingo Molnar <mingo@...e.hu>, tytso@....edu,
	Brian Swetland <swetland@...gle.com>,
	Neil Brown <neilb@...e.de>, Arve Hj?nnev?g <arve@...roid.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	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 Fri, 2010-06-04 at 12:11 +0200, Thomas Gleixner wrote:
> On Fri, 4 Jun 2010, Peter Zijlstra wrote:
> 
> > On Fri, 2010-06-04 at 11:43 +0200, Peter Zijlstra wrote:
> > > I still believe containment is a cgroup problem. The freeze/snapshot/resume
> > > container folks seem to face many of the same problems. Including the
> > > pending timer one I suspect. Lets solve it there. 
> > 
> > While talking to Thomas about this, we'd probably need a CLOCK_MONOTONIC
> > namespace to pull this off, so that resumed apps don't see the jump in
> > absolute time.
> > 
> > This would also help with locating the relevant timers, since they'd be
> > on the related timer base.
> > 
> > The only 'interesting' issue I can see here is that if you create 1000
> > CLOCK_MONOTONIC namepaces, we'd need to have a tree of trees in order to
> > efficiently find the leftmost timer.
> 
> We can do more clever than that. All CLOCK_MONOTONIC timers can live
> in the CLOCK_MONOTONIC rbtree, we just need proper annotation, i.e.:
> 
> struct hrtimer {
>        ktime_t expires;
>        ......
>        struct list_head namespace;
>        ktime_t base_offset;
> };
> 
> So expires would be on CLOCK_MONOTONIC as seen from the kernel, just
> the user space interfaces would take the base_offset into account.
> 
> On freeze we remove the timers from the rbtree (they are easy to
> find via the namespace list) and on thaw we set the base_offset
> accordingly and insert them again. So no surprise for user space and
> no tree of trees to walk through.

Ah indeed, much nicer.
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