linux-kernel - Re: [PATCH 1/3] sched: Add new API wake_up_if

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Message-ID: <20140903095148.GH4783@worktop.ger.corp.intel.com>
Date:	Wed, 3 Sep 2014 11:51:48 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Chuansheng Liu <chuansheng.liu@...el.com>
Cc:	luto@...capital.net, daniel.lezcano@...aro.org, rjw@...ysocki.net,
	mingo@...hat.com, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, changcheng.liu@...el.com,
	xiaoming.wang@...el.com, souvik.k.chakravarty@...el.com
Subject: Re: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the
 idle cpu

On Mon, Aug 18, 2014 at 04:37:30PM +0800, Chuansheng Liu wrote:
> Implementing one new API wake_up_if_idle(), which is used to
> wake up the idle CPU.
> 
> Suggested-by: Andy Lutomirski <luto@...capital.net>
> Signed-off-by: Chuansheng Liu <chuansheng.liu@...el.com>
> ---
>  include/linux/sched.h |    1 +
>  kernel/sched/core.c   |   16 ++++++++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 857ba40..3f89ac1 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1024,6 +1024,7 @@ struct sched_domain_topology_level {
>  extern struct sched_domain_topology_level *sched_domain_topology;
>  
>  extern void set_sched_topology(struct sched_domain_topology_level *tl);
> +extern void wake_up_if_idle(int cpu);
>  
>  #ifdef CONFIG_SCHED_DEBUG
>  # define SD_INIT_NAME(type)		.name = #type
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 1211575..adf104f 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1620,6 +1620,22 @@ static void ttwu_queue_remote(struct task_struct *p, int cpu)
>  	}
>  }
>  
> +void wake_up_if_idle(int cpu)
> +{
> +	struct rq *rq = cpu_rq(cpu);
> +	unsigned long flags;
> +
> +	if (set_nr_if_polling(rq->idle)) {
> +		trace_sched_wake_idle_without_ipi(cpu);
> +	} else {
> +		raw_spin_lock_irqsave(&rq->lock, flags);
> +		if (rq->curr == rq->idle)

That needs to be is_idle_task(), there might be other 'idle' tasks than
rq->idle :/

> +			smp_send_reschedule(cpu);
> +		/* Else cpu is not in idle, do nothing here */
> +		raw_spin_unlock_irqrestore(&rq->lock, flags);
> +	}
> +}
> +
>  bool cpus_share_cache(int this_cpu, int that_cpu)
>  {
>  	return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
> -- 
> 1.7.9.5
> 
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