linux-kernel - Re: [PATCH 21/40] autonuma: avoid CFS select_task_rq

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Date:	Fri, 29 Jun 2012 14:57:53 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Hillf Danton <dhillf@...il.com>, Dan Smith <danms@...ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Johannes Weiner <hannes@...xchg.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Alex Shi <alex.shi@...el.com>,
	Mauricio Faria de Oliveira <mauricfo@...ux.vnet.ibm.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Don Morris <don.morris@...com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 21/40] autonuma: avoid CFS select_task_rq_fair to return
 -1

On 06/28/2012 08:56 AM, Andrea Arcangeli wrote:
> Fix to avoid -1 retval.
>
> Includes fixes from Hillf Danton<dhillf@...il.com>.
>
> Signed-off-by: Andrea Arcangeli<aarcange@...hat.com>
> ---
>   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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