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sched/rtmutex: Refactor rt_mutex_setprio()

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With the introduction of SCHED_DEADLINE the whole notion that priority
is a single number is gone, therefore the @prio argument to
rt_mutex_setprio() doesn't make sense anymore.

So rework the code to pass a pi_task instead.

Note this also fixes a problem with pi_top_task caching; previously we
would not set the pointer (call rt_mutex_update_top_task) if the
priority didn't change, this could lead to a stale pointer.

As for the XXX, I think its fine to use pi_task->prio, because if it
differs from waiter->prio, a PI chain update is immenent.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170323150216.303827095@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Peter Zijlstra
2017-03-23 15:56:11 +01:00
committed by Thomas Gleixner
parent aa2bfe5536
commit acd58620e4
3 changed files with 91 additions and 111 deletions
Download Patch File Download Diff File Expand all files Collapse all files

66
kernel/sched/core.c
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@@ -3671,10 +3671,25 @@ EXPORT_SYMBOL(default_wake_function);
#ifdef CONFIG_RT_MUTEXES
static inline int __rt_effective_prio(struct task_struct *pi_task, int prio)
{
if (pi_task)
prio = min(prio, pi_task->prio);
return prio;
}
static inline int rt_effective_prio(struct task_struct *p, int prio)
{
struct task_struct *pi_task = rt_mutex_get_top_task(p);
return __rt_effective_prio(pi_task, prio);
}
/*
* rt_mutex_setprio - set the current priority of a task
* @p: task
* @prio: prio value (kernel-internal form)
* @p: task to boost
* @pi_task: donor task
*
* This function changes the 'effective' priority of a task. It does
* not touch ->normal_prio like __setscheduler().
@@ -3682,18 +3697,42 @@ EXPORT_SYMBOL(default_wake_function);
* Used by the rt_mutex code to implement priority inheritance
* logic. Call site only calls if the priority of the task changed.
*/
void rt_mutex_setprio(struct task_struct *p, int prio)
void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
{
int oldprio, queued, running, queue_flag =
int prio, oldprio, queued, running, queue_flag =
DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
const struct sched_class *prev_class;
struct rq_flags rf;
struct rq *rq;
BUG_ON(prio > MAX_PRIO);
/* XXX used to be waiter->prio, not waiter->task->prio */
prio = __rt_effective_prio(pi_task, p->normal_prio);
/*
* If nothing changed; bail early.
*/
if (p->pi_top_task == pi_task && prio == p->prio && !dl_prio(prio))
return;
rq = __task_rq_lock(p, &rf);
update_rq_clock(rq);
/*
* Set under pi_lock && rq->lock, such that the value can be used under
* either lock.
*
* Note that there is loads of tricky to make this pointer cache work
* right. rt_mutex_slowunlock()+rt_mutex_postunlock() work together to
* ensure a task is de-boosted (pi_task is set to NULL) before the
* task is allowed to run again (and can exit). This ensures the pointer
* points to a blocked task -- which guaratees the task is present.
*/
p->pi_top_task = pi_task;
/*
* For FIFO/RR we only need to set prio, if that matches we're done.
*/
if (prio == p->prio && !dl_prio(prio))
goto out_unlock;
/*
* Idle task boosting is a nono in general. There is one
@@ -3713,9 +3752,7 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
goto out_unlock;
}
rt_mutex_update_top_task(p);
trace_sched_pi_setprio(p, prio);
trace_sched_pi_setprio(p, prio); /* broken */
oldprio = p->prio;
if (oldprio == prio)
@@ -3739,7 +3776,6 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
* running task
*/
if (dl_prio(prio)) {
struct task_struct *pi_task = rt_mutex_get_top_task(p);
if (!dl_prio(p->normal_prio) ||
(pi_task && dl_entity_preempt(&pi_task->dl, &p->dl))) {
p->dl.dl_boosted = 1;
@@ -3777,6 +3813,11 @@ out_unlock:
balance_callback(rq);
preempt_enable();
}
#else
static inline int rt_effective_prio(struct task_struct *p, int prio)
{
return prio;
}
#endif
void set_user_nice(struct task_struct *p, long nice)
@@ -4023,10 +4064,9 @@ static void __setscheduler(struct rq *rq, struct task_struct *p,
* Keep a potential priority boosting if called from
* sched_setscheduler().
*/
p->prio = normal_prio(p);
if (keep_boost)
p->prio = rt_mutex_get_effective_prio(p, normal_prio(p));
else
p->prio = normal_prio(p);
p->prio = rt_effective_prio(p, p->prio);
if (dl_prio(p->prio))
p->sched_class = &dl_sched_class;
@@ -4313,7 +4353,7 @@ change:
* the runqueue. This will be done when the task deboost
* itself.
*/
new_effective_prio = rt_mutex_get_effective_prio(p, newprio);
new_effective_prio = rt_effective_prio(p, newprio);
if (new_effective_prio == oldprio)
queue_flags &= ~DEQUEUE_MOVE;
}