linux-kernel - Re: [PATCH] sched: Do not stop cpu in set_cpus_allowed

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Date:	Sun, 14 Sep 2014 11:13:38 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Kirill Tkhai <ktkhai@...allels.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	tkhai@...dex.ru
Subject: Re: [PATCH] sched: Do not stop cpu in set_cpus_allowed_ptr() if task
 is not running

On Fri, Sep 12, 2014 at 03:03:34PM +0400, Kirill Tkhai wrote:
> 
> If a task is queued but not running on it rq, we can simply migrate
> it without migration thread and switching of context.
> 
> Signed-off-by: Kirill Tkhai <ktkhai@...allels.com>
> ---
>  kernel/sched/core.c |   47 ++++++++++++++++++++++++++++++++---------------
>  1 file changed, 32 insertions(+), 15 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index d4399b4..dbbba26 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4594,6 +4594,33 @@ void init_idle(struct task_struct *idle, int cpu)
>  }
>  
>  #ifdef CONFIG_SMP
> +/*
> + * move_queued_task - move a queued task to new rq.
> + *
> + * Returns (locked) new rq. Old rq's lock is released.
> + */
> +static struct rq *move_queued_task(struct task_struct *p, int new_cpu)
> +{
> +	struct rq *rq = task_rq(p);
> +
> +	lockdep_assert_held(&rq->lock);
> +
> +	dequeue_task(rq, p, 0);
> +	p->on_rq = TASK_ON_RQ_MIGRATING;
> +	set_task_cpu(p, new_cpu);
> +	raw_spin_unlock(&rq->lock);
> +
> +	rq = cpu_rq(new_cpu);
> +
> +	raw_spin_lock(&rq->lock);
> +	BUG_ON(task_cpu(p) != new_cpu);
> +	p->on_rq = TASK_ON_RQ_QUEUED;
> +	enqueue_task(rq, p, 0);
> +	check_preempt_curr(rq, p, 0);
> +
> +	return rq;
> +}

We have almost that exact code sequence in __migrate_task() could we
share some?
--
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