Commit a0e813f2 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched/core: Further clarify sched_class::set_next_task() 



It turns out there really is something special to the first
set_next_task() invocation. In specific the 'change' pattern really
should not cause balance callbacks.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bsegall@google.com
Cc: dietmar.eggemann@arm.com
Cc: juri.lelli@redhat.com
Cc: ktkhai@virtuozzo.com
Cc: mgorman@suse.de
Cc: qais.yousef@arm.com
Cc: qperret@google.com
Cc: rostedt@goodmis.org
Cc: valentin.schneider@arm.com
Cc: vincent.guittot@linaro.org
Fixes: f95d4eae ("sched/{rt,deadline}: Fix set_next_task vs pick_next_task")
Link: https://lkml.kernel.org/r/20191108131909.775434698@infradead.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 2eeb01a2

kernel/sched/deadline.c

+5 −2
Original line number Diff line number Diff line
@@ -1743,13 +1743,16 @@ static void start_hrtick_dl(struct rq *rq, struct task_struct *p) 
}

#endif



static void set_next_task_dl(struct rq *rq, struct task_struct *p)

static void set_next_task_dl(struct rq *rq, struct task_struct *p, bool first)

{

	p->se.exec_start = rq_clock_task(rq);



	/* You can't push away the running task */

	dequeue_pushable_dl_task(rq, p);



	if (!first)

		return;



	if (hrtick_enabled(rq))

		start_hrtick_dl(rq, p);
@@ -1782,7 +1785,7 @@ static struct task_struct *pick_next_task_dl(struct rq *rq) 
	dl_se = pick_next_dl_entity(rq, dl_rq);

	BUG_ON(!dl_se);

	p = dl_task_of(dl_se);

	set_next_task_dl(rq, p);

	set_next_task_dl(rq, p, true);

	return p;

}

kernel/sched/fair.c

+1 −1
Original line number Diff line number Diff line
@@ -10344,7 +10344,7 @@ static void switched_to_fair(struct rq *rq, struct task_struct *p) 
 * This routine is mostly called to set cfs_rq->curr field when a task

 * migrates between groups/classes.

 */

static void set_next_task_fair(struct rq *rq, struct task_struct *p)

static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)

{

	struct sched_entity *se = &p->se;

kernel/sched/idle.c

+2 −2
Original line number Diff line number Diff line
@@ -385,7 +385,7 @@ static void put_prev_task_idle(struct rq *rq, struct task_struct *prev) 
{

}



static void set_next_task_idle(struct rq *rq, struct task_struct *next)

static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool first)

{

	update_idle_core(rq);

	schedstat_inc(rq->sched_goidle);
@@ -395,7 +395,7 @@ struct task_struct *pick_next_task_idle(struct rq *rq) 
{

	struct task_struct *next = rq->idle;



	set_next_task_idle(rq, next);

	set_next_task_idle(rq, next, true);



	return next;

}

kernel/sched/rt.c

+5 −2
Original line number Diff line number Diff line
@@ -1515,13 +1515,16 @@ static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p, int flag 
#endif

}



static inline void set_next_task_rt(struct rq *rq, struct task_struct *p)

static inline void set_next_task_rt(struct rq *rq, struct task_struct *p, bool first)

{

	p->se.exec_start = rq_clock_task(rq);



	/* The running task is never eligible for pushing */

	dequeue_pushable_task(rq, p);



	if (!first)

		return;



	/*

	 * If prev task was rt, put_prev_task() has already updated the

	 * utilization. We only care of the case where we start to schedule a
@@ -1572,7 +1575,7 @@ static struct task_struct *pick_next_task_rt(struct rq *rq) 
		return NULL;



	p = _pick_next_task_rt(rq);

	set_next_task_rt(rq, p);

	set_next_task_rt(rq, p, true);

	return p;

}

kernel/sched/sched.h

+2 −2
Original line number Diff line number Diff line
@@ -1716,7 +1716,7 @@ struct sched_class { 
	struct task_struct *(*pick_next_task)(struct rq *rq);



	void (*put_prev_task)(struct rq *rq, struct task_struct *p);

	void (*set_next_task)(struct rq *rq, struct task_struct *p);

	void (*set_next_task)(struct rq *rq, struct task_struct *p, bool first);



#ifdef CONFIG_SMP

	int (*balance)(struct rq *rq, struct task_struct *prev, struct rq_flags *rf);
@@ -1768,7 +1768,7 @@ static inline void put_prev_task(struct rq *rq, struct task_struct *prev) 
static inline void set_next_task(struct rq *rq, struct task_struct *next)

{

	WARN_ON_ONCE(rq->curr != next);

	next->sched_class->set_next_task(rq, next);

	next->sched_class->set_next_task(rq, next, false);

}



#ifdef CONFIG_SMP

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