Commit a4c2f00f authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched: fair scheduler should not resched rt tasks 



With use of ftrace Steven noticed that some RT tasks got rescheduled due
to sched_fair interaction.

What happens is that we reprogram the hrtick from enqueue/dequeue_fair_task()
because that can change nr_running, and thus a current tasks ideal runtime.
However, its possible the current task isn't a fair_sched_class task, and thus
doesn't have a hrtick set to change.

Fix this by wrapping those hrtick_start_fair() calls in a hrtick_update()
function, which will check for the right conditions.

Reported-by: default avatarSteven Rostedt <srostedt@redhat.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: default avatarSteven Rostedt <srostedt@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent ffda12a1

kernel/sched_fair.c

+24 −4
Original line number Diff line number Diff line
@@ -73,6 +73,8 @@ unsigned int sysctl_sched_wakeup_granularity = 5000000UL; 


const_debug unsigned int sysctl_sched_migration_cost = 500000UL;



static const struct sched_class fair_sched_class;



/**************************************************************

 * CFS operations on generic schedulable entities:

 */
@@ -848,11 +850,31 @@ static void hrtick_start_fair(struct rq *rq, struct task_struct *p) 
		hrtick_start(rq, delta);

	}

}



/*

 * called from enqueue/dequeue and updates the hrtick when the

 * current task is from our class and nr_running is low enough

 * to matter.

 */

static void hrtick_update(struct rq *rq)

{

	struct task_struct *curr = rq->curr;



	if (curr->sched_class != &fair_sched_class)

		return;



	if (cfs_rq_of(&curr->se)->nr_running < sched_nr_latency)

		hrtick_start_fair(rq, curr);

}

#else /* !CONFIG_SCHED_HRTICK */

static inline void

hrtick_start_fair(struct rq *rq, struct task_struct *p)

{

}



static inline void hrtick_update(struct rq *rq)

{

}

#endif



/*
@@ -873,7 +895,7 @@ static void enqueue_task_fair(struct rq *rq, struct task_struct *p, int wakeup) 
		wakeup = 1;

	}



	hrtick_start_fair(rq, rq->curr);

	hrtick_update(rq);

}



/*
@@ -895,7 +917,7 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int sleep) 
		sleep = 1;

	}



	hrtick_start_fair(rq, rq->curr);

	hrtick_update(rq);

}



/*
@@ -1001,8 +1023,6 @@ static inline int wake_idle(int cpu, struct task_struct *p) 


#ifdef CONFIG_SMP



static const struct sched_class fair_sched_class;



#ifdef CONFIG_FAIR_GROUP_SCHED

/*

 * effective_load() calculates the load change as seen from the root_task_group

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