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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