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

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Date:	Sun, 14 Sep 2014 13:20:32 +0400
From:	Kirill Tkhai <tkhai@...dex.ru>
To:	Peter Zijlstra <peterz@...radead.org>,
	Kirill Tkhai <ktkhai@...allels.com>
CC:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] sched: Do not stop cpu in set_cpus_allowed_ptr() if task
 is not running

On 14.09.2014 13:13, Peter Zijlstra wrote:
> 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?
> 

Peter, haven't I moved the sequence from __migrate_task??

Rechecked again; yes, patch makes __migrate_task using new move_queued_task.

Kirill
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