[PATCH] sched/rt: Don't pull tasks of throttled rt_rq in pre_schedule_rt()
From: Kirill Tkhai <hidden>
Date: 2012-12-25 08:20:59
Also in:
lkml
Subsystem:
scheduler, the rest · Maintainers:
Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot, Linus Torvalds
The patch aims not to pull tasks of throttled rt_rqs in pre_schedule_rt() because thay are not able to be picked in pick_next_task_rt(). There are three places where pull_rt_task() is used: 1)pre_schedule_rt() If we pull a task of a throttled rt_rq it won't be picked by pick_next_task_rt(), because throttled tasks are dequeued by sched_rt_runtime_exceeded(). So this action is unnecessary. 2)prio_changed_rt() A pulled task of higher priority leads to reschedule of current rq's task. The schedule() will occur with the first hw interrupt so there is possibility the throttled rt_rq will unthrottle and it will be queued during this time. (In case of preemptable kernel schedule() occurs during preempt_enable() in call of __task_rq_unlock(). But its lock is unlocked so there is no guarantee the rt_rq won't be queued). 3)switched_from_rt() The same as prio_changed_rt(). Signed-off-by: Kirill V Tkhai <redacted> CC: Steven Rostedt <rostedt@goodmis.org> CC: Ingo Molnar <mingo@kernel.org> CC: Peter Zijlstra <peterz@infradead.org> CC: linux-rt-users --- kernel/sched/rt.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 418feb0..567908a 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c@@ -1708,7 +1708,17 @@ static void push_rt_tasks(struct rq *rq) ; } -static int pull_rt_task(struct rq *this_rq) +static inline int remote_rt_rq_throttled(struct task_struct *p, int remote_cpu) +{ + struct rt_rq *rt_rq = rt_rq_of_se(&p->rt); + struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq); + + rt_rq = sched_rt_period_rt_rq(rt_b, remote_cpu); + + return rt_rq_throttled(rt_rq); +} + +static int pull_rt_task(struct rq *this_rq, bool unthrottled) { int this_cpu = this_rq->cpu, ret = 0, cpu; struct task_struct *p;
@@ -1768,6 +1778,9 @@ static int pull_rt_task(struct rq *this_rq) if (p->prio < src_rq->curr->prio) goto skip; + if (unthrottled && remote_rt_rq_throttled(p, this_cpu)) + goto skip; + ret = 1; deactivate_task(src_rq, p, 0);
@@ -1791,7 +1804,7 @@ static void pre_schedule_rt(struct rq *rq, struct task_struct *prev) { /* Try to pull RT tasks here if we lower this rq's prio */ if (rq->rt.highest_prio.curr > prev->prio) - pull_rt_task(rq); + pull_rt_task(rq, true); } static void post_schedule_rt(struct rq *rq)
@@ -1890,7 +1903,7 @@ static void switched_from_rt(struct rq *rq, struct task_struct *p) * now. */ if (p->on_rq && !rq->rt.rt_nr_running) - pull_rt_task(rq); + pull_rt_task(rq, false); } void init_sched_rt_class(void)
@@ -1949,7 +1962,7 @@ prio_changed_rt(struct rq *rq, struct task_struct *p, int oldprio) * may need to pull tasks to this runqueue. */ if (oldprio < p->prio) - pull_rt_task(rq); + pull_rt_task(rq, false); /* * If there's a higher priority task waiting to run * then reschedule. Note, the above pull_rt_task