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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2008-10-17 13:27:03 -0400
committerIngo Molnar <mingo@elte.hu>2008-10-20 08:05:03 -0400
commita4c2f00f5cb848af7a8c816426b413c8e41834df (patch)
treef99d376ae43fe7e19db0f5f268c6925d8cda2107
parentffda12a17a324103e9900fa1035309811eecbfe5 (diff)
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>
-rw-r--r--kernel/sched_fair.c28
1 files changed, 24 insertions, 4 deletions
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 67084936b602..0c4bcac54761 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -73,6 +73,8 @@ unsigned int sysctl_sched_wakeup_granularity = 5000000UL;
73 73
74const_debug unsigned int sysctl_sched_migration_cost = 500000UL; 74const_debug unsigned int sysctl_sched_migration_cost = 500000UL;
75 75
76static const struct sched_class fair_sched_class;
77
76/************************************************************** 78/**************************************************************
77 * CFS operations on generic schedulable entities: 79 * CFS operations on generic schedulable entities:
78 */ 80 */
@@ -848,11 +850,31 @@ static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
848 hrtick_start(rq, delta); 850 hrtick_start(rq, delta);
849 } 851 }
850} 852}
853
854/*
855 * called from enqueue/dequeue and updates the hrtick when the
856 * current task is from our class and nr_running is low enough
857 * to matter.
858 */
859static void hrtick_update(struct rq *rq)
860{
861 struct task_struct *curr = rq->curr;
862
863 if (curr->sched_class != &fair_sched_class)
864 return;
865
866 if (cfs_rq_of(&curr->se)->nr_running < sched_nr_latency)
867 hrtick_start_fair(rq, curr);
868}
851#else /* !CONFIG_SCHED_HRTICK */ 869#else /* !CONFIG_SCHED_HRTICK */
852static inline void 870static inline void
853hrtick_start_fair(struct rq *rq, struct task_struct *p) 871hrtick_start_fair(struct rq *rq, struct task_struct *p)
854{ 872{
855} 873}
874
875static inline void hrtick_update(struct rq *rq)
876{
877}
856#endif 878#endif
857 879
858/* 880/*
@@ -873,7 +895,7 @@ static void enqueue_task_fair(struct rq *rq, struct task_struct *p, int wakeup)
873 wakeup = 1; 895 wakeup = 1;
874 } 896 }
875 897
876 hrtick_start_fair(rq, rq->curr); 898 hrtick_update(rq);
877} 899}
878 900
879/* 901/*
@@ -895,7 +917,7 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int sleep)
895 sleep = 1; 917 sleep = 1;
896 } 918 }
897 919
898 hrtick_start_fair(rq, rq->curr); 920 hrtick_update(rq);
899} 921}
900 922
901/* 923/*
@@ -1001,8 +1023,6 @@ static inline int wake_idle(int cpu, struct task_struct *p)
1001 1023
1002#ifdef CONFIG_SMP 1024#ifdef CONFIG_SMP
1003 1025
1004static const struct sched_class fair_sched_class;
1005
1006#ifdef CONFIG_FAIR_GROUP_SCHED 1026#ifdef CONFIG_FAIR_GROUP_SCHED
1007/* 1027/*
1008 * effective_load() calculates the load change as seen from the root_task_group 1028 * effective_load() calculates the load change as seen from the root_task_group