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>
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@ -73,6 +73,8 @@ unsigned int sysctl_sched_wakeup_granularity = 5000000UL;
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const_debug unsigned int sysctl_sched_migration_cost = 500000UL;
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const_debug unsigned int sysctl_sched_migration_cost = 500000UL;
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static const struct sched_class fair_sched_class;
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/**************************************************************
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/**************************************************************
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* CFS operations on generic schedulable entities:
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* CFS operations on generic schedulable entities:
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*/
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*/
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@ -848,11 +850,31 @@ static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
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hrtick_start(rq, delta);
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hrtick_start(rq, delta);
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}
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}
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}
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}
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/*
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* called from enqueue/dequeue and updates the hrtick when the
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* current task is from our class and nr_running is low enough
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* to matter.
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*/
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static void hrtick_update(struct rq *rq)
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{
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struct task_struct *curr = rq->curr;
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if (curr->sched_class != &fair_sched_class)
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return;
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if (cfs_rq_of(&curr->se)->nr_running < sched_nr_latency)
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hrtick_start_fair(rq, curr);
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}
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#else /* !CONFIG_SCHED_HRTICK */
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#else /* !CONFIG_SCHED_HRTICK */
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static inline void
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static inline void
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hrtick_start_fair(struct rq *rq, struct task_struct *p)
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hrtick_start_fair(struct rq *rq, struct task_struct *p)
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{
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{
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}
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}
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static inline void hrtick_update(struct rq *rq)
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{
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}
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#endif
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#endif
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/*
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/*
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@ -873,7 +895,7 @@ static void enqueue_task_fair(struct rq *rq, struct task_struct *p, int wakeup)
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wakeup = 1;
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wakeup = 1;
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}
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}
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hrtick_start_fair(rq, rq->curr);
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hrtick_update(rq);
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}
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}
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/*
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/*
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@ -895,7 +917,7 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int sleep)
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sleep = 1;
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sleep = 1;
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}
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}
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hrtick_start_fair(rq, rq->curr);
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hrtick_update(rq);
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}
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}
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/*
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/*
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@ -1001,8 +1023,6 @@ static inline int wake_idle(int cpu, struct task_struct *p)
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#ifdef CONFIG_SMP
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#ifdef CONFIG_SMP
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static const struct sched_class fair_sched_class;
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#ifdef CONFIG_FAIR_GROUP_SCHED
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#ifdef CONFIG_FAIR_GROUP_SCHED
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/*
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/*
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* effective_load() calculates the load change as seen from the root_task_group
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* effective_load() calculates the load change as seen from the root_task_group
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