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

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Date:	Tue, 17 Apr 2012 09:44:14 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
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, 2012-04-17 at 14:09 +0200, Peter Zijlstra wrote:
> 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.
> --

yes, CONFIG_PREEMPT is turned off on my side.  With the patch that you
sent, the slowed down went from a factor of 4 down to a factor 2. 

So the run time is now twice as long vs four time as long vs v3.3
kernel.

Tim

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