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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: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2008-10-17 19:27:03 +02:00 committed by Ingo Molnar
parent ffda12a17a
commit a4c2f00f5c
1 changed files with 24 additions and 4 deletions
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28
kernel/sched_fair.c
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@ -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