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

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Message-Id: <1203949799.4688.9.camel@homer.simson.net>
Date:	Mon, 25 Feb 2008 15:29:59 +0100
From:	Mike Galbraith <efault@....de>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>, Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: revert load_balance_monitor()


On Mon, 2008-02-25 at 13:22 +0100, Peter Zijlstra wrote:
> Subject: sched: 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.
> 
> ( minimal revert - leaves most of the code present, just removes the activation
>   and sysctl interface ).

top - 14:05:56 up 3 min, 16 users,  load average: 4.31, 2.14, 0.85
Tasks: 218 total,   5 running, 213 sleeping,   0 stopped,   0 zombie
Cpu(s): 35.5%us, 64.5%sy,  0.0%ni,  0.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  P COMMAND
 5294 mikeg     20   0  1464  364  304 R   99  0.0   1:00.08 0 chew-max
 5278 root      20   0  1464  364  304 R   32  0.0   0:27.86 1 chew-max
 5279 root      20   0  1464  360  304 R   32  0.0   0:35.53 1 chew-max
 5290 root      20   0  1464  364  304 R   31  0.0   0:29.00 1 chew-max

The minimal revert seems to leave group fairness in a worse state than
what the original patch meant to fix.  Maybe a full revert would be
better?

	-Mike

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