Re: [RFC PATCH 1/2] sched: encapsulate priority changes in a sched_set_prio static function

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

----- On May 27, 2016, at 5:16 PM, Julien Desfossez jdesfossez@efficios.com wrote:

> Currently, the priority of tasks is modified directly in the scheduling
> functions. Encapsulate priority updates to enable instrumentation of
> priority changes. This will enable analysis of real-time scheduling
> delays per thread priority, which cannot be performed accurately if we
> only trace the priority of the currently scheduled processes.
> 
> The call sites that modify the priority of a task are mostly system
> calls: sched_setscheduler, sched_setattr, sched_process_fork and
> set_user_nice. Priority can also be dynamically boosted through
> priority inheritance of rt_mutex by rt_mutex_setprio.
> 
> Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

> ---
> include/linux/sched.h |  3 ++-
> kernel/sched/core.c   | 19 +++++++++++++------
> 2 files changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 52c4847..48b35c0 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1409,7 +1409,8 @@ struct task_struct {
> #endif
> 	int on_rq;
> 
> -	int prio, static_prio, normal_prio;
> +	int prio; /* Updated through sched_set_prio() */
> +	int static_prio, normal_prio;
> 	unsigned int rt_priority;
> 	const struct sched_class *sched_class;
> 	struct sched_entity se;
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index d1f7149..6946b8f 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2230,6 +2230,11 @@ int sysctl_schedstats(struct ctl_table *table, int write,
> #endif
> #endif
> 
> +static void sched_set_prio(struct task_struct *p, int prio)
> +{
> +	p->prio = prio;
> +}
> +
> /*
>  * fork()/clone()-time setup:
>  */
> @@ -2249,7 +2254,7 @@ int sched_fork(unsigned long clone_flags, struct
> task_struct *p)
> 	/*
> 	 * Make sure we do not leak PI boosting priority to the child.
> 	 */
> -	p->prio = current->normal_prio;
> +	sched_set_prio(p, current->normal_prio);
> 
> 	/*
> 	 * Revert to default priority/policy on fork if requested.
> @@ -2262,7 +2267,8 @@ int sched_fork(unsigned long clone_flags, struct
> task_struct *p)
> 		} else if (PRIO_TO_NICE(p->static_prio) < 0)
> 			p->static_prio = NICE_TO_PRIO(0);
> 
> -		p->prio = p->normal_prio = __normal_prio(p);
> +		p->normal_prio = __normal_prio(p);
> +		sched_set_prio(p, p->normal_prio);
> 		set_load_weight(p);
> 
> 		/*
> @@ -3477,7 +3483,7 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
> 		p->sched_class = &fair_sched_class;
> 	}
> 
> -	p->prio = prio;
> +	sched_set_prio(p, prio);
> 
> 	if (running)
> 		p->sched_class->set_curr_task(rq);
> @@ -3524,7 +3530,7 @@ void set_user_nice(struct task_struct *p, long nice)
> 	p->static_prio = NICE_TO_PRIO(nice);
> 	set_load_weight(p);
> 	old_prio = p->prio;
> -	p->prio = effective_prio(p);
> +	sched_set_prio(p, effective_prio(p));
> 	delta = p->prio - old_prio;
> 
> 	if (queued) {
> @@ -3731,9 +3737,10 @@ static void __setscheduler(struct rq *rq, struct
> task_struct *p,
> 	 * sched_setscheduler().
> 	 */
> 	if (keep_boost)
> -		p->prio = rt_mutex_get_effective_prio(p, normal_prio(p));
> +		sched_set_prio(p, rt_mutex_get_effective_prio(p,
> +					normal_prio(p)));
> 	else
> -		p->prio = normal_prio(p);
> +		sched_set_prio(p, normal_prio(p));
> 
> 	if (dl_prio(p->prio))
> 		p->sched_class = &dl_sched_class;
> --
> 1.9.1

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com