Re: [PATCH v2] sched/fair: Care divide error in update_task_scan_period()

[Yasuaki Ishimatsu]

(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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/