linux-kernel - Re: [RFC][PATCH v5 07/14] sched: get CPU's activity statistic

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Message-ID: <20131112104129.GH4971@laptop.programming.kicks-ass.net>
Date:	Tue, 12 Nov 2013 11:41:29 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org, pjt@...gle.com,
	Morten.Rasmussen@....com, cmetcalf@...era.com, tony.luck@...el.com,
	alex.shi@...el.com, preeti@...ux.vnet.ibm.com,
	linaro-kernel@...ts.linaro.org, rjw@...k.pl,
	paulmck@...ux.vnet.ibm.com, corbet@....net, tglx@...utronix.de,
	len.brown@...el.com, arjan@...ux.intel.com,
	amit.kucheria@...aro.org, l.majewski@...sung.com
Subject: Re: [RFC][PATCH v5 07/14] sched: get CPU's activity statistic

On Fri, Oct 18, 2013 at 01:52:20PM +0200, Vincent Guittot wrote:
> +static int get_cpu_activity(int cpu)
> +{
> +	struct rq *rq = cpu_rq(cpu);
> +	u32 sum = rq->avg.runnable_avg_sum;
> +	u32 period = rq->avg.runnable_avg_period;
> +
> +	sum = min(sum, period);
> +
> +	if (sum == period) {
> +		u32 overload = rq->nr_running > 1 ? 1 : 0;
> +		return available_of(cpu) + overload;
> +	}
> +
> +	return (sum * available_of(cpu)) / period;

I'm thinking this has a fair potential to overflow our u32, no?

> +}
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