Messages in this thread |  | | Date | Tue, 21 Oct 2014 11:21:12 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2] sched/fair: Care divide error in update_task_scan_period() |
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On Thu, Oct 16, 2014 at 06:48:15PM +0900, Yasuaki Ishimatsu wrote: > +++ b/kernel/sched/fair.c > @@ -1466,6 +1466,7 @@ static void update_task_scan_period(struct task_struct *p, > > unsigned long remote = p->numa_faults_locality[0]; > unsigned long local = p->numa_faults_locality[1]; > + unsigned long total_faults = shared + private; > > /* > * If there were no record hinting faults then either the task is > @@ -1496,6 +1497,14 @@ static void update_task_scan_period(struct task_struct *p, > slot = 1; > diff = slot * period_slot; > } else { > + /* > + * This is a rare case. total_faults might become 0 after > + * offlining node. In this case, total_faults is set to 1 > + * for avoiding divide error. > + */ > + if (unlikely(total_faults == 0)) > + total_faults = 1; > + > diff = -(NUMA_PERIOD_THRESHOLD - ratio) * period_slot; > > /* > @@ -1506,7 +1515,7 @@ static void update_task_scan_period(struct task_struct *p, > * scanning faster if shared accesses dominate as it may > * simply bounce migrations uselessly > */ > - ratio = DIV_ROUND_UP(private * NUMA_PERIOD_SLOTS, (private + shared)); > + ratio = DIV_ROUND_UP(private * NUMA_PERIOD_SLOTS, (total_faults)); > diff = (diff * ratio) / NUMA_PERIOD_SLOTS;
So what was wrong with the 'normal' unconditional +1 approach? Also you've got superfluous parenthese.
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