linux-kernel - Re: load balancing regression since commit 367456c7

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Message-ID: <1334664553.28150.87.camel@twins>
Date:	Tue, 17 Apr 2012 14:09:13 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	Suresh Siddha <suresh.b.siddha@...el.com>,
	Alex Shi <alex.shi@...el.com>, Ying <ying.huang@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: load balancing regression since commit 367456c7

On Tue, 2012-04-10 at 18:06 -0700, Tim Chen wrote:
>                   |--56.52%-- load_balance
>                   |          idle_balance
>                   |          __schedule
>                   |          schedule 

Ahh, I know why I didn't see it, I have a CONFIG_PREEMPT kernel and
idle_balancing stops once its gotten a single task over instead of
achieving proper balance.

And since hackbench generates insanely long runqueues and the patch that
caused your regression 'fixed' the lock-breaking it will now iterate the
entire runqueue if needed to achieve balance, which hurts.

I think the patch I send ought to work, let me try disabling
CONFIG_PREEMPT.
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