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SubjectRe: [PATCH 1/2] perf_events: add cgroup support (v8)
* Peter Zijlstra <peterz@infradead.org> [2011-02-02 12:29:20]:

> 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?a

Are you suggesting that the cgroup_exit on task_exit notification should be
pulled out?

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

We use pre_destroy() to reclaim, so that delete/rmdir() will be able
to clean up the node/group. I am not sure what you mean by it makes
the empty notification void and why pre_destroy() is broken?

--
Three Cheers,
Balbir


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