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sched: Fix cross-sched-class wakeup preemption 

Instead of dealing with sched classes inside each check_preempt_curr()
implementation, pull out this logic into the generic wakeup preemption
path.

This fixes a hang in KVM (and others) where we are waiting for the
stop machine thread to run ...

Reported-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Tested-by: Marcelo Tosatti <mtosatti@redhat.com>
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1288891946.2039.31.camel@laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2010-10-31 12:37:04 +01:00 committed by Ingo Molnar
parent 2d46709082
commit 1e5a74059f
3 changed files with 27 additions and 18 deletions
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37
kernel/sched.c
View File

@ -560,18 +560,8 @@ struct rq {
static DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
static inline
void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
{
rq->curr->sched_class->check_preempt_curr(rq, p, flags);
/*
* A queue event has occurred, and we're going to schedule. In
* this case, we can save a useless back to back clock update.
*/
if (test_tsk_need_resched(p))
rq->skip_clock_update = 1;
}
static void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags);
static inline int cpu_of(struct rq *rq)
{
@ -2118,6 +2108,31 @@ static inline void check_class_changed(struct rq *rq, struct task_struct *p,
p->sched_class->prio_changed(rq, p, oldprio, running);
}
static void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
{
const struct sched_class *class;
if (p->sched_class == rq->curr->sched_class) {
rq->curr->sched_class->check_preempt_curr(rq, p, flags);
} else {
for_each_class(class) {
if (class == rq->curr->sched_class)
break;
if (class == p->sched_class) {
resched_task(rq->curr);
break;
}
}
}
/*
* A queue event has occurred, and we're going to schedule. In
* this case, we can save a useless back to back clock update.
*/
if (test_tsk_need_resched(rq->curr))
rq->skip_clock_update = 1;
}
#ifdef CONFIG_SMP
/*
* Is this task likely cache-hot:

6
kernel/sched_fair.c
View File

@ -1654,12 +1654,6 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
struct cfs_rq *cfs_rq = task_cfs_rq(curr);
int scale = cfs_rq->nr_running >= sched_nr_latency;
if (unlikely(rt_prio(p->prio)))
goto preempt;
if (unlikely(p->sched_class != &fair_sched_class))
return;
if (unlikely(se == pse))
return;

2
kernel/sched_stoptask.c
View File

@ -19,7 +19,7 @@ select_task_rq_stop(struct rq *rq, struct task_struct *p,
static void
check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
{
resched_task(rq->curr); /* we preempt everything */
/* we're never preempted */
}
static struct task_struct *pick_next_task_stop(struct rq *rq)