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SubjectRe: [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



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