linux-kernel - Re: [PATCH 1/2] nohz: clean up select_nohz_load

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Date:	Mon, 10 Sep 2012 17:26:14 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alex Shi <alex.shi@...el.com>
Cc:	mingo@...hat.com, tglx@...utronix.de, linux-kernel@...r.kernel.org,
	Venkatesh Pallipadi <venki@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [PATCH 1/2] nohz: clean up select_nohz_load_balancer()

On Mon, 2012-09-10 at 15:10 +0800, Alex Shi wrote:
> There is no load_balancer to be selected now. It just set state of
> nohz tick stopping.
> 
> So rename the function, pass the 'cpu' from parameter and then
> remove the useless calling from tick_nohz_restart_sched_tick().

Please check who wrote the code you're patching and attempt to CC them
as well, in this case Venki and Suresh.

I think the patch is fine, although I think we could have picked a
better name, how about nohz_balance_enter_idle() ?

> Signed-off-by: Alex Shi <alex.shi@...el.com>
> ---
>  include/linux/sched.h    |    4 ++--
>  kernel/sched/fair.c      |   19 +++++++------------
>  kernel/time/tick-sched.c |    3 +--
>  3 files changed, 10 insertions(+), 16 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index b8c8664..5cba49c 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -273,11 +273,11 @@ extern void init_idle_bootup_task(struct task_struct *idle);
>  extern int runqueue_is_locked(int cpu);
>  
>  #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ)
> -extern void select_nohz_load_balancer(int stop_tick);
> +extern void set_nohz_tick_stopped(int cpu);
>  extern void set_cpu_sd_state_idle(void);
>  extern int get_nohz_timer_target(void);
>  #else
> -static inline void select_nohz_load_balancer(int stop_tick) { }
> +static inline void set_nohz_tick_stopped(int cpu) { }
>  static inline void set_cpu_sd_state_idle(void) { }
>  #endif
>  
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c219bf8..5bbc4bf 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4674,28 +4674,23 @@ void set_cpu_sd_state_idle(void)
>  }
>  
>  /*
> - * This routine will record that this cpu is going idle with tick stopped.
> + * This routine will record that the cpu is going idle with tick stopped.
>   * This info will be used in performing idle load balancing in the future.
>   */
> -void select_nohz_load_balancer(int stop_tick)
> +void set_nohz_tick_stopped(int cpu)
>  {
> -	int cpu = smp_processor_id();
> -
>  	/*
>  	 * If this cpu is going down, then nothing needs to be done.
>  	 */
>  	if (!cpu_active(cpu))
>  		return;
>  
> -	if (stop_tick) {
> -		if (test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))
> -			return;
> +	if (test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))
> +		return;
>  
> -		cpumask_set_cpu(cpu, nohz.idle_cpus_mask);
> -		atomic_inc(&nohz.nr_cpus);
> -		set_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
> -	}
> -	return;
> +	cpumask_set_cpu(cpu, nohz.idle_cpus_mask);
> +	atomic_inc(&nohz.nr_cpus);
> +	set_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
>  }
>  
>  static int __cpuinit sched_ilb_notifier(struct notifier_block *nfb,
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index 024540f..eacde97 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -372,7 +372,7 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
>  		 * the scheduler tick in nohz_restart_sched_tick.
>  		 */
>  		if (!ts->tick_stopped) {
> -			select_nohz_load_balancer(1);
> +			set_nohz_tick_stopped(cpu);
>  			calc_load_enter_idle();
>  
>  			ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
> @@ -569,7 +569,6 @@ static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
>  static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
>  {
>  	/* Update jiffies first */
> -	select_nohz_load_balancer(0);
>  	tick_do_update_jiffies64(now);
>  	update_cpu_load_nohz();
>  

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