linux-kernel - Re: [PATCH 2/2] CFS CGroup: Report usage

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Message-ID: <20071023024036.GC3324@linux.vnet.ibm.com>
Date:	Tue, 23 Oct 2007 08:10:36 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Paul Menage <menage@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	containers@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] CFS CGroup: Report usage

On Mon, Oct 22, 2007 at 05:49:39PM -0700, Paul Menage wrote:
> +static u64 cpu_usage_read(struct cgroup *cgrp, struct cftype *cft)
> +{
> +	struct task_group *tg = cgroup_tg(cgrp);
> +	int i;
> +	u64 res = 0;
> +	for_each_possible_cpu(i) {
> +		unsigned long flags;
> +		spin_lock_irqsave(&tg->cfs_rq[i]->rq->lock, flags);

Is the lock absolutely required here?

Hmm .. I hope the cgroup code prevents a task group from being destroyed while 
we are still reading a task group's cpu usage. Is that so?

> +		res += tg->se[i]->sum_exec_runtime;
> +		spin_unlock_irqrestore(&tg->cfs_rq[i]->rq->lock, flags);
> +	}
> +	/* Convert from ns to ms */
> +	do_div(res, 1000000);
> +	return res;
> +}

-- 
Regards,
vatsa
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