sched: 64-bit: fix arithmetics overflow
authorLai Jiangshan <laijs@cn.fujitsu.com>
Thu, 12 Jun 2008 08:43:07 +0000 (16:43 +0800)
committerIngo Molnar <mingo@elte.hu>
Thu, 12 Jun 2008 12:29:54 +0000 (14:29 +0200)
commit7a232e0350940d2664f4de5cc3f0f443bae5062d
treebb91a53faab7bf6e92df127f8bdb2225cf808925
parent2e084786f6fe052274f1dfa7c675fe4a02cacd6e
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>
kernel/sched.c