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Subject[PATCH] sched/rt: Fix pull_rt_task() skips not overloaded rqs
Date
The main patch profit is deletion of the following check
at the beginning of pull_rt_task():

if (likely(!rt_overloaded(this_rq)))
return 0;

This check makes pull_rt_task() nearly useless, because
it kills all cases like "last RT task has just gone away".
The check is better suitable for push_rt_task().

So, kill the check, now unusable rt_overloaded() and rto_count.

Move root_domain's refcount to the bottom of the structure
to keep its fields aligned.

Signed-off-by: Kirill Tkhai <tkhai@yandex.ru>
CC: Ingo Molnar <mingo@redhat.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Steven Rostedt <rostedt@goodmis.org>
---
kernel/sched/rt.c | 19 -------------------
kernel/sched/sched.h | 3 +--
2 files changed, 1 insertions(+), 21 deletions(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 01970c8..cf297a7 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -229,26 +229,12 @@ int alloc_rt_sched_group(struct task_group *tg, struct task_group *parent)

#ifdef CONFIG_SMP

-static inline int rt_overloaded(struct rq *rq)
-{
- return atomic_read(&rq->rd->rto_count);
-}
-
static inline void rt_set_overload(struct rq *rq)
{
if (!rq->online)
return;

cpumask_set_cpu(rq->cpu, rq->rd->rto_mask);
- /*
- * Make sure the mask is visible before we set
- * the overload count. That is checked to determine
- * if we should look at the mask. It would be a shame
- * if we looked at the mask, but the mask was not
- * updated yet.
- */
- wmb();
- atomic_inc(&rq->rd->rto_count);
}

static inline void rt_clear_overload(struct rq *rq)
@@ -256,8 +242,6 @@ static inline void rt_clear_overload(struct rq *rq)
if (!rq->online)
return;

- /* the order here really doesn't matter */
- atomic_dec(&rq->rd->rto_count);
cpumask_clear_cpu(rq->cpu, rq->rd->rto_mask);
}

@@ -1627,9 +1611,6 @@ static int pull_rt_task(struct rq *this_rq)
struct task_struct *p;
struct rq *src_rq;

- if (likely(!rt_overloaded(this_rq)))
- return 0;
-
for_each_cpu(cpu, this_rq->rd->rto_mask) {
if (this_cpu == cpu)
continue;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 4c1cb80..1f36afb 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -374,8 +374,6 @@ struct rt_rq {
*
*/
struct root_domain {
- atomic_t refcount;
- atomic_t rto_count;
struct rcu_head rcu;
cpumask_var_t span;
cpumask_var_t online;
@@ -386,6 +384,7 @@ struct root_domain {
*/
cpumask_var_t rto_mask;
struct cpupri cpupri;
+ atomic_t refcount;
};

extern struct root_domain def_root_domain;

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