linux-kernel - Re: [PATCH 3/3] sched: terminate newidle balancing once at least one task has moved over

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Date:	Tue, 24 Jun 2008 12:13:26 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Gregory Haskins <ghaskins@...ell.com>
Cc:	mingo@...e.hu, rostedt@...dmis.org, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	dbahi@...ell.com
Subject: Re: [PATCH 3/3] sched: terminate newidle balancing once at least
	one task has moved over

On Mon, 2008-06-23 at 17:04 -0600, Gregory Haskins wrote:
> Inspired by Peter Zijlstra.
> 
> Signed-off-by: Gregory Haskins <ghaskins@...ell.com>
> ---
> 
>  kernel/sched.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 3efbbc5..c8e8520 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -2775,6 +2775,10 @@ static int move_tasks(struct rq *this_rq, int this_cpu, struct rq *busiest,
>  				max_load_move - total_load_moved,
>  				sd, idle, all_pinned, &this_best_prio);
>  		class = class->next;
> +
> +		if (idle == CPU_NEWLY_IDLE && this_rq->nr_running)
> +			break;
> +
>  	} while (class && max_load_move > total_load_moved);
>  
>  	return total_load_moved > 0;


right,.. uhm, except that you forgot all the other fixes and
generalizations I had,..

The LB_START/LB_COMPLETE stuff is needed to fix CFS load balancing. It
now always iterates the first sysctl_sched_nr_migrate tasks, and if it
doesn't find any there, just gives up - which isn't too big of a problem
with it set to 32, but if you drop it to 2/4 stuff starts valing apart.

And the break I had here, only checks classes above and equal to the
current class.

This again is needed when you have more classes.

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