linux-kernel - Re: [PATCH] sched: revert load_balance

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Message-ID: <20080225155301.GA6787@osiris.boeblingen.de.ibm.com>
Date:	Mon, 25 Feb 2008 16:53:01 +0100
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Mike Galbraith <efault@....de>, Ingo Molnar <mingo@...e.hu>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: revert load_balance_monitor()

On Mon, Feb 25, 2008 at 04:28:02PM +0100, Peter Zijlstra wrote:
> On Mon, 2008-02-25 at 20:05 +0530, Dhaval Giani wrote:
> Subject: sched: fully revert load_balance_monitor()
> 
> The following commit causes a number of serious regressions:
> 
>   commit 6b2d7700266b9402e12824e11e0099ae6a4a6a79
>   Author: Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
>   Date:   Fri Jan 25 21:08:00 2008 +0100
>   sched: group scheduler, fix fairness of cpu bandwidth allocation for task groups
> 
> Namely:
>  - very frequent wakeups on SMP, reported by PowerTop users.
>  - cacheline trashing on (large) SMP
>  - some latencies larger than 500ms
> 
> While there is a mergeable patch to fix the latter, the former issues
> are IMHO not fixable in a manner suitable for .25 (we're at -rc3 now).
> Hence I propose to revert this patch and try again for .26.

I was just about to complain about the frequent wakeups caused by the
original patch.
It's responsible of 70% of wakeups on an otherwise idle system on s390.

Thanks :)
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