linux-kernel - Re: [PATCH 2/4] sched/fair: Introduce idle enter/exit balance callbacks

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Date:	Mon, 20 Jun 2016 16:30:03 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jiri Olsa <jolsa@...nel.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	James Hartsock <hartsjc@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Kirill Tkhai <ktkhai@...allels.com>
Subject: Re: [PATCH 2/4] sched/fair: Introduce idle enter/exit balance
 callbacks

On Mon, Jun 20, 2016 at 02:15:12PM +0200, Jiri Olsa wrote:
> Introducing idle enter/exit balance callbacks to keep
> balance.idle_cpus_mask cpumask of current idle cpus
> in system.
> 
> It's used only when REBALANCE_AFFINITY feature is
> switched on. The code functionality of this feature
> is introduced in following patch.
> 
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  kernel/sched/fair.c  | 32 ++++++++++++++++++++++++++++++++
>  kernel/sched/idle.c  |  2 ++
>  kernel/sched/sched.h |  3 +++
>  3 files changed, 37 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index f19c9435c64d..78c4127f2f3a 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7802,6 +7802,37 @@ static inline int on_null_domain(struct rq *rq)
>  	return unlikely(!rcu_dereference_sched(rq->sd));
>  }
>  
> +static struct {
> +	cpumask_var_t	idle_cpus_mask;
> +	atomic_t	nr_cpus;
> +} balance ____cacheline_aligned;

How is this different from the nohz idle cpu mask?