linux-kernel - Re: [PATCH 2/2] sched: trigger_load

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Date:	Tue, 11 Sep 2012 11:36:12 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Alex Shi <alex.shi@...el.com>
Cc:	mingo@...hat.com, peterz@...radead.org, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, venki@...gle.com
Subject: Re: [PATCH 2/2] sched: trigger_load_balance clean up

On Mon, 2012-09-10 at 15:10 +0800, Alex Shi wrote:
> Remove a redundant check for on_null_domain(cpu), and rerange the code
> that make it more readable.

hmm, but we are now doing the on_null_domain() check always,
irrespective of whether we need the load balance or not.

do we really need the on_null_domain() check there? What happens if we
just remove it?

thanks,
suresh

> 
> Signed-off-by: Alex Shi <alex.shi@...el.com>
> ---
>  kernel/sched/fair.c |    8 +++++---
>  1 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 5bbc4bf..529092d 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4934,11 +4934,13 @@ static inline int on_null_domain(int cpu)
>  void trigger_load_balance(struct rq *rq, int cpu)
>  {
>  	/* Don't need to rebalance while attached to NULL domain */
> -	if (time_after_eq(jiffies, rq->next_balance) &&
> -	    likely(!on_null_domain(cpu)))
> +	if (unlikely(on_null_domain(cpu)))
> +		return;
> +
> +	if (time_after_eq(jiffies, rq->next_balance))
>  		raise_softirq(SCHED_SOFTIRQ);
>  #ifdef CONFIG_NO_HZ
> -	if (nohz_kick_needed(rq, cpu) && likely(!on_null_domain(cpu)))
> +	if (nohz_kick_needed(rq, cpu))
>  		nohz_balancer_kick(cpu);
>  #endif
>  }


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