Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...

[mirror_ubuntu-artful-kernel.git] / kernel / sched / core.c

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e628cb11b5606306e11f456471022fa65488976b..5eab11d4b747df5a5ff75a9e6558444c37b5c18a 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1814,6 +1814,10 @@ void __dl_clear_params(struct task_struct *p)
        dl_se->dl_period = 0;
        dl_se->flags = 0;
        dl_se->dl_bw = 0;
+
+       dl_se->dl_throttled = 0;
+       dl_se->dl_new = 1;
+       dl_se->dl_yielded = 0;
 }
 
 /*
@@ -1839,7 +1843,7 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
 #endif
 
        RB_CLEAR_NODE(&p->dl.rb_node);
-       hrtimer_init(&p->dl.dl_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+       init_dl_task_timer(&p->dl);
        __dl_clear_params(p);
 
        INIT_LIST_HEAD(&p->rt.run_list);
@@ -2049,6 +2053,9 @@ static inline int dl_bw_cpus(int i)
  * allocated bandwidth to reflect the new situation.
  *
  * This function is called while holding p's rq->lock.
+ *
+ * XXX we should delay bw change until the task's 0-lag point, see
+ * __setparam_dl().
  */
 static int dl_overflow(struct task_struct *p, int policy,
                       const struct sched_attr *attr)
@@ -3251,15 +3258,31 @@ __setparam_dl(struct task_struct *p, const struct sched_attr *attr)
 {
        struct sched_dl_entity *dl_se = &p->dl;
 
-       init_dl_task_timer(dl_se);
        dl_se->dl_runtime = attr->sched_runtime;
        dl_se->dl_deadline = attr->sched_deadline;
        dl_se->dl_period = attr->sched_period ?: dl_se->dl_deadline;
        dl_se->flags = attr->sched_flags;
        dl_se->dl_bw = to_ratio(dl_se->dl_period, dl_se->dl_runtime);
-       dl_se->dl_throttled = 0;
-       dl_se->dl_new = 1;
-       dl_se->dl_yielded = 0;
+
+       /*
+        * Changing the parameters of a task is 'tricky' and we're not doing
+        * the correct thing -- also see task_dead_dl() and switched_from_dl().
+        *
+        * What we SHOULD do is delay the bandwidth release until the 0-lag
+        * point. This would include retaining the task_struct until that time
+        * and change dl_overflow() to not immediately decrement the current
+        * amount.
+        *
+        * Instead we retain the current runtime/deadline and let the new
+        * parameters take effect after the current reservation period lapses.
+        * This is safe (albeit pessimistic) because the 0-lag point is always
+        * before the current scheduling deadline.
+        *
+        * We can still have temporary overloads because we do not delay the
+        * change in bandwidth until that time; so admission control is
+        * not on the safe side. It does however guarantee tasks will never
+        * consume more than promised.
+        */
 }
 
 /*
@@ -4642,6 +4665,9 @@ int cpuset_cpumask_can_shrink(const struct cpumask *cur,
        struct dl_bw *cur_dl_b;
        unsigned long flags;
 
+       if (!cpumask_weight(cur))
+               return ret;
+
        rcu_read_lock_sched();
        cur_dl_b = dl_bw_of(cpumask_any(cur));
        trial_cpus = cpumask_weight(trial);