On Wed, Oct 08, 2014 at 03:43:11PM +0900, Yasuaki Ishimatsu wrote:
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index bfa3c86..fb7dc3f 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1496,18 +1496,26 @@ static void update_task_scan_period(struct
> task_struct *p,
> slot = 1;
> diff = slot * period_slot;
> } else {
> - diff = -(NUMA_PERIOD_THRESHOLD - ratio) * period_slot;
> + if (unlikely((private + shared) == 0))
> + /*
> + * This is a rare case. The trigger is node offline.
> + */
> + diff = 0;
> + else {
> + diff = -(NUMA_PERIOD_THRESHOLD - ratio) * period_slot;
>
> - /*
> - * Scale scan rate increases based on sharing. There is an
> - * inverse relationship between the degree of sharing and
> - * the adjustment made to the scanning period. Broadly
> - * speaking the intent is that there is little point
> - * scanning faster if shared accesses dominate as it may
> - * simply bounce migrations uselessly
> - */
> - ratio = DIV_ROUND_UP(private * NUMA_PERIOD_SLOTS, (private +
> shared));
> - diff = (diff * ratio) / NUMA_PERIOD_SLOTS;
> + /*
> + * Scale scan rate increases based on sharing. There is
> + * an inverse relationship between the degree of sharing
> + * and the adjustment made to the scanning period.
> + * Broadly speaking the intent is that there is little
> + * point scanning faster if shared accesses dominate as
> + * it may simply bounce migrations uselessly
> + */
> + ratio = DIV_ROUND_UP(private * NUMA_PERIOD_SLOTS,
> + (private + shared));
> + diff = (diff * ratio) / NUMA_PERIOD_SLOTS;
> + }
> }
>
> p->numa_scan_period = clamp(p->numa_scan_period + diff,
Yeah, so I don't like the patch nor do I really like the function as it
stands -- which I suppose is part of why I don't like the patch.
The problem I have with the function is that its very inconsistent in
behaviour. In the early return path it sets numa_scan_period and
numa_next_scan, in the later return path it sets numa_scan_period and
numa_faults_locality.
I feel both return paths should affect the same set of variables, esp.
the non clearing of numa_faults_locality in the early path seems weird.
The thing I suppose I don't like about the patch is its added
indentation and the fact that the simple +1 thing wasn't considered.
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