Re: [PATCH 21/40] autonuma: avoid CFS select_task_rq_fair to return-1

[Rik van Riel]

On 06/28/2012 08:56 AM, Andrea Arcangeli wrote:
> Fix to avoid -1 retval.
>
> Includes fixes from Hillf Danton<dhillf@xxxxxxxxx>.
>
> Signed-off-by: Andrea Arcangeli<aarcange@xxxxxxxxxx>
> ---
>   kernel/sched/fair.c |    4 ++++
>   1 files changed, 4 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c099cc6..fa96810 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -2789,6 +2789,9 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
>   		if (new_cpu == -1 || new_cpu == cpu) {
>   			/* Now try balancing at a lower domain level of cpu */
>   			sd = sd->child;
> +			if (new_cpu<  0)
> +				/* Return prev_cpu is find_idlest_cpu failed */
> +				new_cpu = prev_cpu;
>   			continue;
>   		}
>
> @@ -2807,6 +2810,7 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
>   unlock:
>   	rcu_read_unlock();
>
> +	BUG_ON(new_cpu<  0);
>   	return new_cpu;
>   }
>   #endif /* CONFIG_SMP */

Wait, what?

Either this is a scheduler bugfix, in which case you
are better off submitting it separately and reducing
the size of your autonuma patch queue, or this is a
behaviour change in the scheduler that needs better
arguments than a 1-line changelog.

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