linux-kernel - Re: [PATCH 1/2] sched: calculate_imbalance: Fix local->avg_load > sds->avg

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Date:	Mon, 16 Sep 2013 10:11:32 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	Ingo Molnar <mingo@...nel.org>, Paul Turner <pjt@...gle.com>,
	linux-kernel@...r.kernel.org, devel@...nvz.org
Subject: Re: [PATCH 1/2] sched: calculate_imbalance: Fix local->avg_load >
 sds->avg_load case

On Mon, Sep 16, 2013 at 12:06:08PM +0400, Vladimir Davydov wrote:
> On 09/16/2013 09:52 AM, Peter Zijlstra wrote:
> >On Sun, Sep 15, 2013 at 05:49:13PM +0400, Vladimir Davydov wrote:

> >>-	if (busiest->avg_load < sds->avg_load) {
> >>+	if (busiest->avg_load <= sds->avg_load ||
> >>+	    local->avg_load >= sds->avg_load) {
> >>  		env->imbalance = 0;
> >>  		return fix_small_imbalance(env, sds);
> >>  	}
> >Why the = part? Surely 'busiest->avg_load < sds->avg_load ||
> >local->avg_load > sds->avg_load' avoids both underflows?
> 
> Of course it does, but env->imbalance will be assigned to 0 anyway in =
> case, so why not go shortcut?

D'uh right.. hadn't had my morning juice yet.
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