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authorVincent Guittot <vincent.guittot@linaro.org>2013-04-18 18:34:26 +0200
committerIngo Molnar <mingo@kernel.org>2013-04-21 11:22:52 +0200
commit642dbc39ab1ea00f47e0fee1b8e8a27da036d940 (patch)
tree337e3cd2be83a916577f78c4819fafe6d29c99c8 /kernel/sched/idle_task.c
parent9b89f6ba2ab56e4d9c00e7e591d6bc333137895e (diff)
downloadlinux-642dbc39ab1ea00f47e0fee1b8e8a27da036d940.tar.bz2
sched: Fix wrong rq's runnable_avg update with rt tasks
The current update of the rq's load can be erroneous when RT tasks are involved. The update of the load of a rq that becomes idle, is done only if the avg_idle is less than sysctl_sched_migration_cost. If RT tasks and short idle duration alternate, the runnable_avg will not be updated correctly and the time will be accounted as idle time when a CFS task wakes up. A new idle_enter function is called when the next task is the idle function so the elapsed time will be accounted as run time in the load of the rq, whatever the average idle time is. The function update_rq_runnable_avg is removed from idle_balance. When a RT task is scheduled on an idle CPU, the update of the rq's load is not done when the rq exit idle state because CFS's functions are not called. Then, the idle_balance, which is called just before entering the idle function, updates the rq's load and makes the assumption that the elapsed time since the last update, was only running time. As a consequence, the rq's load of a CPU that only runs a periodic RT task, is close to LOAD_AVG_MAX whatever the running duration of the RT task is. A new idle_exit function is called when the prev task is the idle function so the elapsed time will be accounted as idle time in the rq's load. Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Steven Rostedt <rostedt@goodmis.org> Cc: linaro-kernel@lists.linaro.org Cc: peterz@infradead.org Cc: pjt@google.com Cc: fweisbec@gmail.com Cc: efault@gmx.de Link: http://lkml.kernel.org/r/1366302867-5055-1-git-send-email-vincent.guittot@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched/idle_task.c')
-rw-r--r--kernel/sched/idle_task.c16
1 files changed, 16 insertions, 0 deletions
diff --git a/kernel/sched/idle_task.c b/kernel/sched/idle_task.c
index b6baf370cae9..b8ce77328341 100644
--- a/kernel/sched/idle_task.c
+++ b/kernel/sched/idle_task.c
@@ -13,6 +13,16 @@ select_task_rq_idle(struct task_struct *p, int sd_flag, int flags)
{
return task_cpu(p); /* IDLE tasks as never migrated */
}
+
+static void pre_schedule_idle(struct rq *rq, struct task_struct *prev)
+{
+ idle_exit_fair(rq);
+}
+
+static void post_schedule_idle(struct rq *rq)
+{
+ idle_enter_fair(rq);
+}
#endif /* CONFIG_SMP */
/*
* Idle tasks are unconditionally rescheduled:
@@ -25,6 +35,10 @@ static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int fl
static struct task_struct *pick_next_task_idle(struct rq *rq)
{
schedstat_inc(rq, sched_goidle);
+#ifdef CONFIG_SMP
+ /* Trigger the post schedule to do an idle_enter for CFS */
+ rq->post_schedule = 1;
+#endif
return rq->idle;
}
@@ -86,6 +100,8 @@ const struct sched_class idle_sched_class = {
#ifdef CONFIG_SMP
.select_task_rq = select_task_rq_idle,
+ .pre_schedule = pre_schedule_idle,
+ .post_schedule = post_schedule_idle,
#endif
.set_curr_task = set_curr_task_idle,