linux-kernel - Re: [RFC PATCH v3 4/6] sched: secure access to other CPU statistics

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Message-ID: <1364302242.5053.19.camel@laptop>
Date:	Tue, 26 Mar 2013 13:50:42 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org, mingo@...nel.org,
	linux@....linux.org.uk, pjt@...gle.com, santosh.shilimkar@...com,
	morten.rasmussen@....com, chander.kashyap@...aro.org,
	cmetcalf@...era.com, tony.luck@...el.com, alex.shi@...el.com,
	preeti@...ux.vnet.ibm.com, paulmck@...ux.vnet.ibm.com,
	tglx@...utronix.de, len.brown@...el.com, arjan@...ux.intel.com,
	amit.kucheria@...aro.org, corbet@....net
Subject: Re: [RFC PATCH v3 4/6] sched: secure access to other CPU statistics

On Fri, 2013-03-22 at 13:25 +0100, Vincent Guittot wrote:
> @@ -3364,13 +3364,16 @@ done:
>  static bool is_buddy_busy(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);

OK this makes sense; use a simple sanity constraint instead of going
overboard on serialization -- however, why is this a separate patch?

That is, this could easily be part of the patch that introduces
is_buddy_busy(); also you likely want part of this patch's changelog
to become a comment that goes right above this min() :-)

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