Messages in this thread |  | | Date | Wed, 22 Oct 2014 14:39:04 +0900 | From | Yasuaki Ishimatsu <> | Subject | Re: [PATCH v2] sched/fair: Care divide error in update_task_scan_period() |
| |
(2014/10/21 18:21), Peter Zijlstra wrote: > 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. >
When (private + shared) was not 0, I did not want to change behavior of update_task_scan_period(). But I understood your comment. I'll update it.
Thanks, Yasuaki Ishimatsu
|  |