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

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Date:	Wed, 2 Feb 2011 17:20:12 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	eranian@...gle.com, linux-kernel@...r.kernel.org, mingo@...e.hu,
	paulus@...ba.org, davem@...emloft.net, fweisbec@...il.com,
	perfmon2-devel@...ts.sf.net, eranian@...il.com,
	robert.richter@....com, acme@...hat.com, lizf@...fujitsu.com,
	Paul Menage <menage@...gle.com>
Subject: Re: [PATCH 1/2] perf_events: add cgroup support (v8)

* Peter Zijlstra <peterz@...radead.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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