From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <a.p.zijlstra-/NLkJaSkS4VmR6Xm/wNWPw@public.gmane.org>
Subject: Re: [PATCH v3 3/6] expose fine-grained per-cpu data for cpuacct
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Date: Wed, 30 May 2012 12:43:48 +0200
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To: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devel-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org, Paul Turner <pjt-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>, handai.szj-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, Andrew.Phillips-xheW4WVAX9Y@public.gmane.org, Serge Hallyn <serge.hallyn-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>

On Wed, 2012-05-30 at 14:34 +0400, Glauber Costa wrote:
> On 05/30/2012 02:34 PM, Peter Zijlstra wrote:
> > On Wed, 2012-05-30 at 13:48 +0400, Glauber Costa wrote:
> >
> >> +static int cpuacct_stats_percpu_show(struct cgroup *cgrp, struct cftype *cft,
> >> +				     struct cgroup_map_cb *cb)
> >> +{
> >> +	struct cpuacct *ca = cgroup_ca(cgrp);
> >> +	int cpu;
> >> +
> >> +	for_each_online_cpu(cpu) {
> >> +		do_fill_cb(cb, ca, "user", cpu, CPUTIME_USER);
> >> +		do_fill_cb(cb, ca, "nice", cpu, CPUTIME_NICE);
> >> +		do_fill_cb(cb, ca, "system", cpu, CPUTIME_SYSTEM);
> >> +		do_fill_cb(cb, ca, "irq", cpu, CPUTIME_IRQ);
> >> +		do_fill_cb(cb, ca, "softirq", cpu, CPUTIME_SOFTIRQ);
> >> +		do_fill_cb(cb, ca, "guest", cpu, CPUTIME_GUEST);
> >> +		do_fill_cb(cb, ca, "guest_nice", cpu, CPUTIME_GUEST_NICE);
> >> +	}
> >> +
> >> +	return 0;
> >> +}
> >
> > Uhm, hotplug anyone?
> What's with hotplug ?


Who's to say all cpus are online at this point? If you don't want to
make the files come and go with hotplug, one should use
for_each_possible_cpu().