[RFC PATCH 1/2] sched: encapsulate priority changes in a sched_set_prio static function

Julien Desfossez
2016-05-27T15:26:25Z

Currently, the priority of tasks is modified directly in the scheduling
functions. Encapsulate priority updates to enable instrumentation of
priority changes. This will enable analysis of real-time scheduling
delays per thread priority, which cannot be performed accurately if we
only trace the priority of the currently scheduled processes.

The call sites that modify the priority of a task are mostly system
calls: sched_setscheduler, sched_setattr, sched_process_fork and
set_user_nice. Priority can also be dynamically boosted through
priority inheritance of rt_mutex by rt_mutex_setprio.

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
---
include/linux/sched.h | 3 ++-
kernel/sched/core.c | 19 +++++++++++++------
2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 52c4847..48b35c0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1409,7 +1409,8 @@ struct task_struct {
#endif
int on_rq;

- int prio, static_prio, normal_prio;
+ int prio; /* Updated through sched_set_prio() */
+ int static_prio, normal_prio;
unsigned int rt_priority;
const struct sched_class *sched_class;
struct sched_entity se;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d1f7149..6946b8f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2230,6 +2230,11 @@ int sysctl_schedstats(struct ctl_table *table, int write,
#endif
#endif

+static void sched_set_prio(struct task_struct *p, int prio)
+{
+ p->prio = prio;
+}
+
/*
* fork()/clone()-time setup:
*/
@@ -2249,7 +2254,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
/*
* Make sure we do not leak PI boosting priority to the child.
*/
- p->prio = current->normal_prio;
+ sched_set_prio(p, current->normal_prio);

/*
* Revert to default priority/policy on fork if requested.
@@ -2262,7 +2267,8 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
} else if (PRIO_TO_NICE(p->static_prio) < 0)
p->static_prio = NICE_TO_PRIO(0);

- p->prio = p->normal_prio = __normal_prio(p);
+ p->normal_prio = __normal_prio(p);
+ sched_set_prio(p, p->normal_prio);
set_load_weight(p);

/*
@@ -3477,7 +3483,7 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
p->sched_class = &fair_sched_class;
}

- p->prio = prio;
+ sched_set_prio(p, prio);

if (running)
p->sched_class->set_curr_task(rq);
@@ -3524,7 +3530,7 @@ void set_user_nice(struct task_struct *p, long nice)
p->static_prio = NICE_TO_PRIO(nice);
set_load_weight(p);
old_prio = p->prio;
- p->prio = effective_prio(p);
+ sched_set_prio(p, effective_prio(p));
delta = p->prio - old_prio;

if (queued) {
@@ -3731,9 +3737,10 @@ static void __setscheduler(struct rq *rq, struct task_struct *p,
* sched_setscheduler().
*/
if (keep_boost)
- p->prio = rt_mutex_get_effective_prio(p, normal_prio(p));
+ sched_set_prio(p, rt_mutex_get_effective_prio(p,
+ normal_prio(p)));
else
- p->prio = normal_prio(p);
+ sched_set_prio(p, normal_prio(p));

if (dl_prio(p->prio))
p->sched_class = &dl_sched_class;
--
1.9.1