sched: Simplify sys_sched_rr_get_interval() system call

By removing the need for it to know details of scheduling classes.

This allows PlugSched to define orthogonal scheduling classes.

Signed-off-by: Peter Williams <pwil3058@bigpond.net.au>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <06d1b89ee15a0eef82d7.1253496713@mudlark.pw.nest>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

5 files changed, 44 insertions, 16 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index cc37a3fa5065..239c8e0dba9f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1075,6 +1075,8 @@ struct sched_class {
         void (*prio_changed) (struct rq *this_rq, struct task_struct *task,
                              int oldprio, int running);
 
+        unsigned int (*get_rr_interval) (struct task_struct *task);
+
 #ifdef CONFIG_FAIR_GROUP_SCHED
         void (*moved_group) (struct task_struct *p);
 #endif
diff --git a/kernel/sched.c b/kernel/sched.c
index 1b900fb1c6e1..830967e18285 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6819,23 +6819,8 @@ SYSCALL_DEFINE2(sched_rr_get_interval, pid_t, pid,
         if (retval)
                 goto out_unlock;
 
-        /*
-         * Time slice is 0 for SCHED_FIFO tasks and for SCHED_OTHER
-         * tasks that are on an otherwise idle runqueue:
-         */
-        time_slice = 0;
-        if (p->policy == SCHED_RR) {
-                time_slice = DEF_TIMESLICE;
-        } else if (p->policy != SCHED_FIFO) {
-                struct sched_entity *se = &p->se;
-                unsigned long flags;
-                struct rq *rq;
+        time_slice = p->sched_class->get_rr_interval(p);
 
-                rq = task_rq_lock(p, &flags);
-                if (rq->cfs.load.weight)
-                        time_slice = NS_TO_JIFFIES(sched_slice(&rq->cfs, se));
-                task_rq_unlock(rq, &flags);
-        }
         read_unlock(&tasklist_lock);
         jiffies_to_timespec(time_slice, &t);
         retval = copy_to_user(interval, &t, sizeof(t)) ? -EFAULT : 0;
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 566e3bb78ed9..cd73738f0d5f 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1938,6 +1938,25 @@ static void moved_group_fair(struct task_struct *p)
 }
 #endif
 
+unsigned int get_rr_interval_fair(struct task_struct *task)
+{
+        struct sched_entity *se = &task->se;
+        unsigned long flags;
+        struct rq *rq;
+        unsigned int rr_interval = 0;
+
+        /*
+         * Time slice is 0 for SCHED_OTHER tasks that are on an otherwise
+         * idle runqueue:
+         */
+        rq = task_rq_lock(task, &flags);
+        if (rq->cfs.load.weight)
+                rr_interval = NS_TO_JIFFIES(sched_slice(&rq->cfs, se));
+        task_rq_unlock(rq, &flags);
+
+        return rr_interval;
+}
+
 /*
  * All the scheduling class methods:
  */
@@ -1966,6 +1985,8 @@ static const struct sched_class fair_sched_class = {
         .prio_changed           = prio_changed_fair,
         .switched_to            = switched_to_fair,
 
+        .get_rr_interval        = get_rr_interval_fair,
+
 #ifdef CONFIG_FAIR_GROUP_SCHED
         .moved_group            = moved_group_fair,
 #endif
diff --git a/kernel/sched_idletask.c b/kernel/sched_idletask.c
index a8b448af004b..b133a28fcde3 100644
--- a/kernel/sched_idletask.c
+++ b/kernel/sched_idletask.c
@@ -97,6 +97,11 @@ static void prio_changed_idle(struct rq *rq, struct task_struct *p,
                 check_preempt_curr(rq, p, 0);
 }
 
+unsigned int get_rr_interval_idle(struct task_struct *task)
+{
+        return 0;
+}
+
 /*
  * Simple, special scheduling class for the per-CPU idle tasks:
  */
@@ -122,6 +127,8 @@ static const struct sched_class idle_sched_class = {
         .set_curr_task          = set_curr_task_idle,
         .task_tick              = task_tick_idle,
 
+        .get_rr_interval        = get_rr_interval_idle,
+
         .prio_changed           = prio_changed_idle,
         .switched_to            = switched_to_idle,
 
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 13de7126a6ab..a4d790cddb19 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1734,6 +1734,17 @@ static void set_curr_task_rt(struct rq *rq)
         dequeue_pushable_task(rq, p);
 }
 
+unsigned int get_rr_interval_rt(struct task_struct *task)
+{
+        /*
+         * Time slice is 0 for SCHED_FIFO tasks
+         */
+        if (task->policy == SCHED_RR)
+                return DEF_TIMESLICE;
+        else
+                return 0;
+}
+
 static const struct sched_class rt_sched_class = {
         .next                   = &fair_sched_class,
         .enqueue_task           = enqueue_task_rt,
@@ -1762,6 +1773,8 @@ static const struct sched_class rt_sched_class = {
         .set_curr_task          = set_curr_task_rt,
         .task_tick              = task_tick_rt,
 
+        .get_rr_interval        = get_rr_interval_rt,
+
         .prio_changed           = prio_changed_rt,
         .switched_to            = switched_to_rt,
 };