linux-kernel - Re: [RFC PATCH] sched: Update cpu

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Date:	Fri, 21 Feb 2014 12:44:07 -0800
From:	Sai <sgurrappadi@...dia.com>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	"peterz@...radead.org" <peterz@...radead.org>,
	"mingo@...hat.com" <mingo@...hat.com>, <pboonstoppel@...dia.com>,
	<pwalmsley@...dia.com>, <fweisbec@...il.com>
Subject: Re: [RFC PATCH] sched: Update cpu_load before nohz ilb

+ More people.

On 02/20/2014 02:06 PM, Sai wrote:
> Update the cpu_load of the kickee in run_rebalance_domains before
> calling rebalance_domains if the kickee is in nohz_idle. This avoids
> using stale cpu_load for the subsequent load_balance.
> 
> cpu_load in the nohz path is updated on tick_nohz_idle_exit or if a
> kickee performances balancing on the behalf of tickless cpus in
> nohz_idle_balance. However, the kickee's cpu_load is never updated if it
> doesn't exit nohz_idle. This causes stale cpu_load to be used which
> causes incorrect load balancing decisions.
> 
> Tested on k3.10.
> 
> Signed-off-by: Sai Gurrappadi <sgurrappadi@...dia.com>
> ---
>  kernel/sched/fair.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 860a152..1d4eb4a 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7140,6 +7140,13 @@ static void run_rebalance_domains(struct
> softirq_action *h)
>         enum cpu_idle_type idle = this_rq->idle_balance ?
>                                                 CPU_IDLE : CPU_NOT_IDLE;
> 
> +       if (test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_rq->cpu))) {
> +               raw_spin_lock_irq(&this_rq->lock);
> +               update_rq_clock(this_rq);
> +               update_idle_cpu_load(this_rq);
> +               raw_spin_unlock_irq(&this_rq->lock);
> +       }
> +
>         rebalance_domains(this_rq, idle);
> 
>         /*
> 
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