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Date: Tue, 25 Dec 2012 12:20:52 +0400
From: Kirill Tkhai <tkhai@...dex.ru>
To: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
linux-rt-users <linux-rt-users@...r.kernel.org>
Subject: [PATCH] sched/rt: Don't pull tasks of throttled rt_rq in pre_schedule_rt()
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 <tkhai@...dex.ru>
CC: Steven Rostedt <rostedt@...dmis.org>
CC: Ingo Molnar <mingo@...nel.org>
CC: Peter Zijlstra <peterz@...radead.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
--
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