From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Glauber Costa <glommer@parallels.com>
Cc: Balbir Singh <bsingharora@gmail.com>,
linux-kernel@vger.kernel.org, paul@paulmenage.org,
lizf@cn.fujitsu.com, daniel.lezcano@free.fr,
jbottomley@parallels.com
Subject: Re: [RFD 3/9] Display /proc/stat information per cgroup
Date: Wed, 28 Sep 2011 00:21:47 +0200 [thread overview]
Message-ID: <1317162107.21836.35.camel@twins> (raw)
In-Reply-To: <4E821920.3000509@parallels.com>
On Tue, 2011-09-27 at 15:42 -0300, Glauber Costa wrote:
> >> +static inline void task_cgroup_account_field(struct task_struct *p,
> >> + cputime64_t tmp, int index)
> >> +{
> >> + struct kernel_stat *kstat;
> >> + struct task_group *tg = task_group(p);
> >> +
> >> + do {
> >> + kstat = this_cpu_ptr(tg->cpustat);
> >> + kstat->cpustat[index] = cputime64_add(kstat->cpustat[index],
> >> + tmp);
> >> + tg = tg->parent;
> >> + } while (tg);
> >> +}
> >
> > What protects the walk (tg = tg->parent)? Could you please document it
> I think that the fact that the hierarchy only grows down, thus parent
> never changes (or am I wrong?)
>
> And since we run all this with preempt disabled and with the runqueue
> locked, we should have no problems.
>
> Do you agree?
Right, so the tg can't be destroyed unless its empty, us finding this
task in it means its not empty, we require rq->lock or p->pi_lock to
move the task.
However, afaict we don't actually have any of those locks.
That said, it should be sufficient to wrap the whole thing in
rcu_read_lock(), accounting one tick funny because a cgroup move race
isn't the end of the world and its really no different than moving the
task a little later anyway.
task_group() should complain about this if you compile a kernel with
CONFIG_PROVE_RCU.
next prev parent reply other threads:[~2011-09-27 22:22 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-23 22:20 [RFD 0/9] per-cgroup /proc/stat statistics Glauber Costa
2011-09-23 22:20 ` [RFD 1/9] Change cpustat fields to an array Glauber Costa
2011-09-27 21:00 ` Peter Zijlstra
2011-09-28 15:13 ` Glauber Costa
2011-09-28 15:23 ` Peter Zijlstra
2011-09-28 18:19 ` Glauber Costa
2011-09-28 19:09 ` Peter Zijlstra
2011-09-28 20:04 ` Glauber Costa
2011-10-01 17:47 ` Glauber Costa
2011-09-27 21:03 ` Peter Zijlstra
2011-09-28 15:14 ` Glauber Costa
2011-09-23 22:20 ` [RFD 2/9] Move /proc/stat logic inside sched.c Glauber Costa
2011-09-23 22:20 ` [RFD 3/9] Display /proc/stat information per cgroup Glauber Costa
2011-09-27 17:01 ` Balbir Singh
2011-09-27 18:42 ` Glauber Costa
2011-09-27 22:21 ` Peter Zijlstra [this message]
2011-09-28 15:22 ` Glauber Costa
2011-09-28 15:23 ` Glauber Costa
2011-09-27 21:48 ` Peter Zijlstra
2011-09-28 15:14 ` Glauber Costa
2011-09-27 21:52 ` Peter Zijlstra
2011-09-28 15:15 ` Glauber Costa
2011-09-23 22:20 ` [RFD 4/9] Make total_forks per-cgroup Glauber Costa
2011-09-27 22:00 ` Peter Zijlstra
2011-09-28 8:13 ` Martin Schwidefsky
2011-09-28 10:35 ` Peter Zijlstra
2011-09-28 12:42 ` Martin Schwidefsky
2011-09-28 12:53 ` Peter Zijlstra
2011-09-28 15:29 ` Glauber Costa
2011-09-28 15:33 ` Peter Zijlstra
2011-09-28 15:35 ` Glauber Costa
2011-09-28 15:37 ` Peter Zijlstra
2011-09-28 15:39 ` Glauber Costa
2011-09-28 15:28 ` Glauber Costa
2011-09-28 15:27 ` Glauber Costa
2011-09-28 15:26 ` Glauber Costa
2011-09-23 22:20 ` [RFD 5/9] per-cgroup boot time Glauber Costa
2011-09-23 22:20 ` [RFD 6/9] Report steal time for cgroup Glauber Costa
2011-09-23 22:20 ` [RFD 7/9] provide a version of cpuacct statistics inside cpu cgroup Glauber Costa
2011-09-23 22:20 ` [RFD 8/9] provide a version of cpuusage " Glauber Costa
2011-09-23 22:20 ` [RFD 9/9] Change CPUACCT to default n Glauber Costa
2011-09-27 22:11 ` [RFD 0/9] per-cgroup /proc/stat statistics Peter Zijlstra
2011-09-28 15:21 ` Glauber Costa
2011-09-28 15:27 ` Peter Zijlstra
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