Date: Fri, 4 Jun 2010 12:11:37 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
cc: Ingo Molnar <mingo@elte.hu>, tytso@mit.edu,
       Brian Swetland <swetland@google.com>, Neil Brown <neilb@suse.de>,
       Arve Hj?nnev?g <arve@android.com>, "Rafael J. Wysocki" <rjw@sisk.pl>,
       Alan Stern <stern@rowland.harvard.edu>,
       Felipe Balbi <felipe.balbi@nokia.com>,
       LKML <linux-kernel@vger.kernel.org>,
       Florian Mickler <florian@mickler.org>,
       Linux OMAP Mailing List <linux-omap@vger.kernel.org>,
       Linux PM <linux-pm@lists.linux-foundation.org>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>,
       James Bottomley <James.Bottomley@suse.de>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Kevin Hilman <khilman@deeprootsystems.com>,
       "H. Peter Anvin" <hpa@zytor.com>,
       Arjan van de Ven <arjan@infradead.org>
Subject: Re: suspend blockers & Android integration
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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.

Thanks,

	tglx
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