linux-kernel - Re: sched: Improve load balancing in the presence of idle CPUs

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Message-ID: <1428438263.2556.74.camel@j-VirtualBox>
Date:	Tue, 07 Apr 2015 13:24:23 -0700
From:	Jason Low <jason.low2@...com>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	Morten Rasmussen <morten.rasmussen@....com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"riel@...hat.com" <riel@...hat.com>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"srikar@...ux.vnet.ibm.com" <srikar@...ux.vnet.ibm.com>,
	"pjt@...gle.com" <pjt@...gle.com>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	"efault@....de" <efault@....de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"iamjoonsoo.kim@....com" <iamjoonsoo.kim@....com>,
	"svaidy@...ux.vnet.ibm.com" <svaidy@...ux.vnet.ibm.com>,
	jason.low2@...com
Subject: Re: sched: Improve load balancing in the presence of idle CPUs

On Tue, 2015-04-07 at 12:39 -0700, Tim Chen wrote:

> How about consolidating the code for passing the
> nohz balancing and call it at both places.  
> Something like below.  Make the code more readable.
> 
> Tim
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 40667cb..16f6904 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7531,6 +7531,15 @@ out:
>  }
>  
>  #ifdef CONFIG_NO_HZ_COMMON
> +static inline int nohz_kick_needed(struct rq *rq);
> +
> +static void inline pass_nohz_balance(struct rq *this_rq, int this_cpu)
> +{
> +       clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu));
> +       if (nohz_kick_needed(this_rq))
> +               nohz_balancer_kick();
> +}
> +
>  /*
>   * In CONFIG_NO_HZ_COMMON case, the idle balance kickee will do the
>   * rebalancing for all the cpus for whom scheduler ticks are stopped.
> @@ -7542,8 +7551,10 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
>         int balance_cpu;
>  
>         if (idle != CPU_IDLE ||
> -           !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)))
> -               goto end;
> +           !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu))) {
> +               pass_nohz_balance(this_rq, this_cpu);
> +               return;
> +       }

Sure, this can make it more readable. This also avoids the need for the
goto, in addition to removing the done_balancing boolean.

Thanks,
Jason

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