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Date: Thu, 14 Jan 2016 22:27:04 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Byungchul Park <byungchul.park@lge.com>,
        Chris Metcalf <cmetcalf@ezchip.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Luiz Capitulino <lcapitulino@redhat.com>,
        Christoph Lameter <cl@linux.com>,
        "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
        Mike Galbraith <efault@gmx.de>, Rik van Riel <riel@redhat.com>
Subject: Re: [RFC PATCH 0/4] sched: Improve cpu load accounting with nohz
Message-ID: <20160114212704.GJ6357@twins.programming.kicks-ass.net>
References: <1452700891-21807-1-git-send-email-fweisbec@gmail.com>
 <569810C4.7090900@arm.com>
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On Thu, Jan 14, 2016 at 09:19:00PM +0000, Dietmar Eggemann wrote:
> @@ -4346,7 +4346,10 @@ static void __update_cpu_load(struct rq *this_rq, unsigned long this_load,
> 
>                 /* scale is effectively 1 << i now, and >> i divides by scale */
> 
> -               old_load = this_rq->cpu_load[i] - tickless_load;
> +               if (this_rq->cpu_load[i] > tickless_load)
> +                       old_load = this_rq->cpu_load[i] - tickless_load;
> +               else
> +                       old_load = 0;

Yeah, yuck. That'd go bad quick.