linux-kernel - Re: [patch] export percpu cpuacct cgroup stats

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Message-Id: <20081206232714.4b34b2fc.akpm@linux-foundation.org>
Date:	Sat, 6 Dec 2008 23:27:14 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ken Chen <kenchen@...gle.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Li Zefan <lizf@...fujitsu.com>,
	Paul Menage <menage@...gle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [patch] export percpu cpuacct cgroup stats

On Fri, 5 Dec 2008 10:16:30 -0800 Ken Chen <kenchen@...gle.com> wrote:

> +static int cpuacct_percpu_seq_read(struct cgroup *cgroup, struct cftype *cft,
> +				   struct seq_file *m)
> +{
> +	struct cpuacct *ca = cgroup_ca(cgroup);
> +	u64 percpu;
> +	int i;
> +
> +	for_each_possible_cpu(i) {
> +		spin_lock_irq(&cpu_rq(i)->lock);
> +		percpu = *percpu_ptr(ca->cpuusage, i);
> +		spin_unlock_irq(&cpu_rq(i)->lock);
> +		seq_printf(m, "%llu ", (unsigned long long) percpu);
> +	}
> +	seq_printf(m, "\n");
> +	return 0;
> +}

The locking is only needed for 32-bit, I assume?

The iteration across all possible CPUs seems a bit lame - that code
looks pretty easy to convert to hotplug goodness.

(All of which pertains to existing code, not to this patch).
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