linux-kernel - Re: [PATCH RESEND] nohz: Affining unpinned timers

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Message-ID: <558A598D.5080900@linux.vnet.ibm.com>
Date:	Wed, 24 Jun 2015 12:47:33 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	Vatika Harlalka <vatikaharlalka@...il.com>, fweisbec@...il.com
CC:	mingo@...hat.com, peterz@...radead.org, rafael.j.wysocki@...el.com,
	tglx@...utronix.de, schwidefsky@...ibm.com,
	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	cl@...ux.com, cmetcalf@...hip.com, bitbucket@...ine.de
Subject: Re: [PATCH RESEND] nohz: Affining unpinned timers

On 06/23/2015 02:01 PM, Vatika Harlalka wrote:
> The problem addressed in this patch is about affining unpinned timers.
> Adaptive or Full Dynticks CPUs should not be disturbed by unnecessary
> jitter due to firing of such timers on them.
> This patch will affine timers to online CPUs which are not Full Dynticks
> in FULL_NOHZ configured systems. It will not bring about functional
> changes if NOHZ_FULL is not configured, because is_housekeeping_cpu()
> always returns true in CONFIG_NO_HZ_FULL=n.
> 
> Signed-off by: Vatika Harlalka <vatikaharlalka@...il.com>
> ---

Reviewed-by: Preeti U Murthy <preeti@...ux.vnet.ibm.com>

>  Changes: Patch sent to the right recipients.
> 
>  include/linux/tick.h | 9 ++++++++-
>  kernel/sched/core.c  | 9 +++++++--
>  2 files changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/tick.h b/include/linux/tick.h
> index f8492da5..145bcba 100644
> --- a/include/linux/tick.h
> +++ b/include/linux/tick.h
> @@ -133,13 +133,20 @@ static inline bool tick_nohz_full_cpu(int cpu)
> 
>  	return cpumask_test_cpu(cpu, tick_nohz_full_mask);
>  }
> -
> +static inline int housekeeping_any_cpu(void)
> +{
> +	return cpumask_any_and(housekeeping_mask, cpu_online_mask);
> +}
>  extern void __tick_nohz_full_check(void);
>  extern void tick_nohz_full_kick(void);
>  extern void tick_nohz_full_kick_cpu(int cpu);
>  extern void tick_nohz_full_kick_all(void);
>  extern void __tick_nohz_task_switch(struct task_struct *tsk);
>  #else
> +static inline int housekeeping_any_cpu(void)
> +{
> +	return smp_processor_id();
> +}
>  static inline bool tick_nohz_full_enabled(void) { return false; }
>  static inline bool tick_nohz_full_cpu(int cpu) { return false; }
>  static inline void __tick_nohz_full_check(void) { }
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 57bd333..acee856 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -599,18 +599,23 @@ int get_nohz_timer_target(int pinned)
>  	int i;
>  	struct sched_domain *sd;
> 
> -	if (pinned || !get_sysctl_timer_migration() || !idle_cpu(cpu))
> +	if (pinned || !get_sysctl_timer_migration() ||
> +		(!idle_cpu(cpu) && is_housekeeping_cpu(cpu)))
>  		return cpu;
> 
>  	rcu_read_lock();
>  	for_each_domain(cpu, sd) {
>  		for_each_cpu(i, sched_domain_span(sd)) {
> -			if (!idle_cpu(i)) {
> +			if (!idle_cpu(i) && is_housekeeping_cpu(cpu)) {
>  				cpu = i;
>  				goto unlock;
>  			}
>  		}
>  	}
> +
> +	if (!is_housekeeping_cpu(cpu))
> +		cpu = housekeeping_any_cpu();
> +
>  unlock:
>  	rcu_read_unlock();
>  	return cpu;
> 

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