Messages in this thread Patch in this message | | | Date | Thu, 12 Jun 2008 16:43:07 +0800 | From | Lai Jiangshan <> | Subject | [PATCH 2/2] sched: 64bit: fix overflow(was: fix divide by zero) |
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(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 be overflow when entities are too many.
Although, overflow is very hardly occurred, but it break fairness when it is occurred. And 64bits system have more memory than 32bits system and 64bits system can create more process usually, so overflow many be occurred more.
This patch guarantee fairness when overflow in 64bits system. Thanks to the optimization of compiler, it change nothing in 32bits system.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> --- diff --git a/kernel/sched.c b/kernel/sched.c index bfb8ad8..e277533 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -1337,8 +1337,13 @@ 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; /*
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