From: Lai Jiangshan <laijs@cn.fujitsu.com>
Date: Thu, 12 Jun 2008 08:43:07 +0000 (+0800)
Subject: sched: 64-bit: fix arithmetics overflow
X-Git-Tag: v2.6.26-rc6~2^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7a232e0350940d2664f4de5cc3f0f443bae5062d;p=pandora-kernel.git

sched: 64-bit: fix arithmetics overflow

(overflow means weight >= 2^32 here, because inv_weigh = 2^32/weight)

A weight of a cfs_rq is the sum of weights of which entities
are queued on this cfs_rq, so it will overflow when there are
too many entities.

Although, overflow occurs very rarely, but it break fairness when
it occurs. 64-bits systems have more memory than 32-bit systems
and 64-bit systems can create more process usually, so overflow may
occur more frequently.

This patch guarantees fairness when overflow happens on 64-bit systems.
Thanks to the optimization of compiler, it changes nothing on 32-bit.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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