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authorLai Jiangshan <laijs@cn.fujitsu.com>2008-06-12 16:43:07 +0800
committerIngo Molnar <mingo@elte.hu>2008-06-12 14:29:54 +0200
commit7a232e0350940d2664f4de5cc3f0f443bae5062d (patch)
treebb91a53faab7bf6e92df127f8bdb2225cf808925 /kernel/sched.c
parent2e084786f6fe052274f1dfa7c675fe4a02cacd6e (diff)
downloadlwn-7a232e0350940d2664f4de5cc3f0f443bae5062d.tar.gz
lwn-7a232e0350940d2664f4de5cc3f0f443bae5062d.zip
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>
Diffstat (limited to 'kernel/sched.c')
-rw-r--r--kernel/sched.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index 6c1ecbdc0db9..eaf6751e7612 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1340,8 +1340,13 @@ calc_delta_mine(unsigned long delta_exec, unsigned long weight,
{
u64 tmp;
- if (!lw->inv_weight)
- lw->inv_weight = 1 + (WMULT_CONST-lw->weight/2)/(lw->weight+1);
+ if (!lw->inv_weight) {
+ if (BITS_PER_LONG > 32 && unlikely(lw->weight >= WMULT_CONST))
+ lw->inv_weight = 1;
+ else
+ lw->inv_weight = 1 + (WMULT_CONST-lw->weight/2)
+ / (lw->weight+1);
+ }
tmp = (u64)delta_exec * weight;
/*