linux-kernel - Re: [PATCH v5 6/7] sched: consider runnable load average in move

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Date:	Mon, 6 May 2013 01:53:44 -0700
From:	Paul Turner <pjt@...gle.com>
To:	Alex Shi <alex.shi@...el.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Namhyung Kim <namhyung@...nel.org>,
	Mike Galbraith <efault@....de>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Michael Wang <wangyun@...ux.vnet.ibm.com>
Subject: Re: [PATCH v5 6/7] sched: consider runnable load average in move_tasks

On Sun, May 5, 2013 at 6:45 PM, Alex Shi <alex.shi@...el.com> wrote:
> Except using runnable load average in background, move_tasks is also
> the key functions in load balance. We need consider the runnable load
> average in it in order to the apple to apple load comparison.
>
> Signed-off-by: Alex Shi <alex.shi@...el.com>
> ---
>  kernel/sched/fair.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 0bf88e8..790e23d 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3966,6 +3966,12 @@ static unsigned long task_h_load(struct task_struct *p);
>
>  static const unsigned int sched_nr_migrate_break = 32;
>
> +static unsigned long task_h_load_avg(struct task_struct *p)
> +{
> +       return div_u64(task_h_load(p) * (u64)p->se.avg.runnable_avg_sum,
> +                       p->se.avg.runnable_avg_period + 1);

Similarly, I think you also want to at least include blocked_load_avg here.

More fundamentally:
I suspect the instability from comparing these to an average taken on
them will not give a representative imbalance weight.  While we should
be no worse off than the present situation; we could be doing much
better.

Consider that by not consuming {runnable, blocked}_load_avg directly
you are "hiding" the movement from one load-balancer to the next.
> +}
> +
>  /*
>   * move_tasks tries to move up to imbalance weighted load from busiest to
>   * this_rq, as part of a balancing operation within domain "sd".
> @@ -4001,7 +4007,7 @@ static int move_tasks(struct lb_env *env)
>                 if (throttled_lb_pair(task_group(p), env->src_cpu, env->dst_cpu))
>                         goto next;
>
> -               load = task_h_load(p);
> +               load = task_h_load_avg(p);
>
>                 if (sched_feat(LB_MIN) && load < 16 && !env->sd->nr_balance_failed)
>                         goto next;
> --
> 1.7.12
>
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