Re: [PATCH 1/2] perf_events: add cgroup support (v8)

[Peter Zijlstra <peterz@infradead.org>]

On Thu, 2011-01-20 at 15:39 +0100, Peter Zijlstra wrote:
> On Thu, 2011-01-20 at 15:30 +0200, Stephane Eranian wrote:
> > @@ -4259,8 +4261,20 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks)
> >  
> >         /* Reassign the task to the init_css_set. */
> >         task_lock(tsk);
> > +       /*
> > +        * we mask interrupts to prevent:
> > +        * - timer tick to cause event rotation which
> > +        *   could schedule back in cgroup events after
> > +        *   they were switched out by perf_cgroup_sched_out()
> > +        *
> > +        * - preemption which could schedule back in cgroup events
> > +        */
> > +       local_irq_save(flags);
> > +       perf_cgroup_sched_out(tsk);
> >         cg = tsk->cgroups;
> >         tsk->cgroups = &init_css_set;
> > +       perf_cgroup_sched_in(tsk);
> > +       local_irq_restore(flags);
> >         task_unlock(tsk);
> >         if (cg)
> >                 put_css_set_taskexit(cg); 
> 
> So you too need a callback on cgroup change there.. Li, Paul, any chance
> we can fix this cgroup_subsys::exit callback? The scheduler code needs
> to do funny thing because its in the wrong place as well.

cgroup guys? Shall I just fix this exit thing since the only user seems
to be the scheduler and now perf for both of which its unfortunate at
best?

Balbir, memcontrol.c uses pre_destroy(), I pose that using this method
is broken per definition since it makes the cgroup empty notification
void.