Re: suspend blockers & Android integration

[Thomas Gleixner]

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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