linux-kernel - Re: [PATCH 05/16] sched: add an rq migration call-back to sched

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Date:	Fri, 29 Jun 2012 10:32:30 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Paul Turner <pjt@...gle.com>
Cc:	linux-kernel@...r.kernel.org, Venki Pallipadi <venki@...gle.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com>,
	Mike Galbraith <efault@....de>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Ben Segall <bsegall@...gle.com>, Ingo Molnar <mingo@...e.hu>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Subject: Re: [PATCH 05/16] sched: add an rq migration call-back to sched_class

On Wed, 27 Jun 2012 19:24:14 -0700, Paul Turner wrote:
> Since we are now doing bottom up load accumulation we need explicit
> notification when a task has been re-parented so that the old hierarchy can be
> updated.
>
> Adds task_migrate_rq(struct rq *prev, struct *rq new_rq);

It should be:
	migrate_task_rq(struct task_struct *p, int next_cpu);


>
> (The alternative is to do this out of __set_task_cpu, but it was suggested that
> this would be a cleaner encapsulation.)
>
> Signed-off-by: Paul Turner <pjt@...gle.com>
> ---
>  include/linux/sched.h |    1 +
>  kernel/sched/core.c   |    2 ++
>  kernel/sched/fair.c   |   12 ++++++++++++
>  3 files changed, 15 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 842c4df..fdfdfab 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1102,6 +1102,7 @@ struct sched_class {
>  
>  #ifdef CONFIG_SMP
>  	int  (*select_task_rq)(struct task_struct *p, int sd_flag, int flags);
> +	void (*migrate_task_rq)(struct task_struct *p, int next_cpu);
>  
>  	void (*pre_schedule) (struct rq *this_rq, struct task_struct *task);
>  	void (*post_schedule) (struct rq *this_rq);
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index aeb8e56..c3686eb 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1109,6 +1109,8 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
>  	trace_sched_migrate_task(p, new_cpu);
>  
>  	if (task_cpu(p) != new_cpu) {
> +		if (p->sched_class->migrate_task_rq)
> +			p->sched_class->migrate_task_rq(p, new_cpu);
>  		p->se.nr_migrations++;
>  		perf_sw_event(PERF_COUNT_SW_CPU_MIGRATIONS, 1, NULL, 0);
>  	}
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 6200d20..33f582a 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3089,6 +3089,17 @@ unlock:
>  
>  	return new_cpu;
>  }
> +
> +/*
> + * Called immediately before a task is migrated to a new cpu; task_cpu(p) and
> + * cfs_rq_of(p) references at time of call are still valid and identify the
> + * previous cpu.  However, the caller only guarantees p->pi_lock is held; no
> + * other assumptions, including rq->lock state, should be made.
> + * Caller guarantees p->pi_lock held, but nothing else.

Duplicate sentence?


> + */
> +static void
> +migrate_task_rq_fair(struct task_struct *p, int next_cpu) {

The opening brace should start on the next line.

Thanks,
Namhyung

> +}
>  #endif /* CONFIG_SMP */
>  
>  static unsigned long
> @@ -5754,6 +5765,7 @@ const struct sched_class fair_sched_class = {
>  
>  #ifdef CONFIG_SMP
>  	.select_task_rq		= select_task_rq_fair,
> +	.migrate_task_rq	= migrate_task_rq_fair,
>  
>  	.rq_online		= rq_online_fair,
>  	.rq_offline		= rq_offline_fair,
--
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