From: Luca Abeni <luca.ab...@unitn.it>
This patch implements a more theoretically sound algorithm for
tracking active utilization: instead of decreasing it when a
task blocks, use a timer (the "inactive timer", named after the
"Inactive" task state of the GRUB algorithm) to decrease the
active utilization at the so called "0-lag time".
Signed-off-by: Luca Abeni <luca.ab...@unitn.it>
---
include/linux/sched.h | 18 +++++-
kernel/sched/core.c | 2 +
kernel/sched/deadline.c | 150 ++++++++++++++++++++++++++++++++++++++++++++----
kernel/sched/sched.h | 1 +
4 files changed, 158 insertions(+), 13 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4d19052..f34633c2 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1451,14 +1451,30 @@ struct sched_dl_entity {
*
* @dl_yielded tells if task gave up the cpu before consuming
* all its available runtime during the last job.
+ *
+ * @dl_non_contending tells if task is inactive while still
+ * contributing to the active utilization. In other words, it
+ * indicates if the inactive timer has been armed and its handler
+ * has not been executed yet. This flag is useful to avoid race
+ * conditions between the inactive timer handler and the wakeup
+ * code.
*/
- int dl_throttled, dl_boosted, dl_yielded;
+ int dl_throttled, dl_boosted, dl_yielded, dl_non_contending;
/*
* Bandwidth enforcement timer. Each -deadline task has its
* own bandwidth to be enforced, thus we need one timer per task.
*/
struct hrtimer dl_timer;
+
+ /*
+ * Inactive timer, responsible for decreasing the active utilization
+ * at the "0-lag time". When a -deadline task blocks, it contributes
+ * to GRUB's active utilization until the "0-lag time", hence a
+ * timer is needed to decrease the active utilization at the correct
+ * time.
+ */
+ struct hrtimer inactive_timer;
};
union rcu_special {
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c56fb57..98f9944 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2187,6 +2187,7 @@ void __dl_clear_params(struct task_struct *p)
dl_se->dl_throttled = 0;
dl_se->dl_yielded = 0;
+ dl_se->dl_non_contending = 0;
}
/*
@@ -2218,6 +2219,7 @@ static void __sched_fork(unsigned long clone_flags,
struct task_struct *p)
RB_CLEAR_NODE(&p->dl.rb_node);
init_dl_task_timer(&p->dl);
+ init_inactive_task_timer(&p->dl);
__dl_clear_params(p);
INIT_LIST_HEAD(&p->rt.run_list);
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 23c840e..cdb7274 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -65,6 +65,46 @@ void sub_running_bw(struct sched_dl_entity *dl_se, struct
dl_rq *dl_rq)
dl_rq->running_bw = 0;
}
+static void task_go_inactive(struct task_struct *p)
+{
+ struct sched_dl_entity *dl_se = &p->dl;
+ struct hrtimer *timer = &dl_se->inactive_timer;
+ struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
+ struct rq *rq = rq_of_dl_rq(dl_rq);
+ s64 zerolag_time;
+
+ WARN_ON(dl_se->dl_runtime == 0);
+
+ WARN_ON(hrtimer_active(&dl_se->inactive_timer));
+ WARN_ON(dl_se->dl_non_contending);
+
+ zerolag_time = dl_se->deadline -
+ div64_long((dl_se->runtime * dl_se->dl_period),
+ dl_se->dl_runtime);
+
+ /*
+ * Using relative times instead of the absolute "0-lag time"
+ * allows to simplify the code
+ */
+ zerolag_time -= rq_clock(rq);
+
+ /*
+ * If the "0-lag time" already passed, decrease the active
+ * utilization now, instead of starting a timer
+ */
+ if (zerolag_time < 0) {
+ sub_running_bw(dl_se, dl_rq);
+ if (!dl_task(p))
+ __dl_clear_params(p);
+
+ return;
+ }
+
+ dl_se->dl_non_contending = 1;
+ get_task_struct(p);
+ hrtimer_start(timer, ns_to_ktime(zerolag_time), HRTIMER_MODE_REL);
+}
+
static inline int is_leftmost(struct task_struct *p, struct dl_rq *dl_rq)
{
struct sched_dl_entity *dl_se = &p->dl;
@@ -610,10 +650,8 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer
*timer)
* The task might have changed its scheduling policy to something
* different than SCHED_DEADLINE (through switched_from_dl()).
*/
- if (!dl_task(p)) {
- __dl_clear_params(p);
+ if (!dl_task(p))
goto unlock;
- }
/*
* The task might have been boosted by someone else and might be in the
@@ -800,6 +838,48 @@ static void update_curr_dl(struct rq *rq)
}
}
+static enum hrtimer_restart inactive_task_timer(struct hrtimer *timer)
+{
+ struct sched_dl_entity *dl_se = container_of(timer,
+ struct sched_dl_entity,
+ inactive_timer);
+ struct task_struct *p = dl_task_of(dl_se);
+ struct rq_flags rf;
+ struct rq *rq;
+
+ rq = task_rq_lock(p, &rf);
+
+ if (!dl_task(p) || p->state == TASK_DEAD) {
+ if (p->state == TASK_DEAD && dl_se->dl_non_contending)
+ sub_running_bw(&p->dl, dl_rq_of_se(&p->dl));
+
+ __dl_clear_params(p);
+
+ goto unlock;
+ }
+ if (dl_se->dl_non_contending == 0)
+ goto unlock;
+
+ sched_clock_tick();
+ update_rq_clock(rq);
+
+ sub_running_bw(dl_se, &rq->dl);
+ dl_se->dl_non_contending = 0;
+unlock:
+ task_rq_unlock(rq, p, &rf);
+ put_task_struct(p);
+
+ return HRTIMER_NORESTART;
+}
+
+void init_inactive_task_timer(struct sched_dl_entity *dl_se)
+{
+ struct hrtimer *timer = &dl_se->inactive_timer;
+
+ hrtimer_init(timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+ timer->function = inactive_task_timer;
+}
+
#ifdef CONFIG_SMP
static void inc_dl_deadline(struct dl_rq *dl_rq, u64 deadline)
@@ -934,7 +1014,28 @@ enqueue_dl_entity(struct sched_dl_entity *dl_se,
if (flags & ENQUEUE_WAKEUP) {
struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
- add_running_bw(dl_se, dl_rq);
+ if (dl_se->dl_non_contending) {
+ /*
+ * If the timer handler is currently running and the
+ * timer cannot be cancelled, inactive_task_timer()
+ * will see that dl_not_contending is not set, and
+ * will do nothing, so we are still safe.
+ */
+ if (hrtimer_try_to_cancel(&dl_se->inactive_timer) == 1)
+ put_task_struct(dl_task_of(dl_se));
+ WARN_ON(dl_task_of(dl_se)->nr_cpus_allowed > 1);
+ dl_se->dl_non_contending = 0;
+ } else {
+ /*
+ * Since "dl_non_contending" is not set, the
+ * task's utilization has already been removed from
+ * active utilization (either when the task blocked,
+ * when the "inactive timer" fired, or when it has
+ * been cancelled in select_task_rq_dl()).
+ * So, add it back.
+ */
+ add_running_bw(dl_se, dl_rq);
+ }
update_dl_entity(dl_se, pi_se);
}
else if (flags & ENQUEUE_REPLENISH)
@@ -1023,7 +1124,7 @@ static void dequeue_task_dl(struct rq *rq, struct
task_struct *p, int flags)
* or "inactive")
*/
if (flags & DEQUEUE_SLEEP)
- sub_running_bw(&p->dl, &rq->dl);
+ task_go_inactive(p);
}
/*
@@ -1097,6 +1198,22 @@ select_task_rq_dl(struct task_struct *p, int cpu, int
sd_flag, int flags)
}
rcu_read_unlock();
+ rq = task_rq(p);
+ raw_spin_lock(&rq->lock);
+ if (p->dl.dl_non_contending) {
+ sub_running_bw(&p->dl, &rq->dl);
+ p->dl.dl_non_contending = 0;
+ /*
+ * If the timer handler is currently running and the
+ * timer cannot be cancelled, inactive_task_timer()
+ * will see that dl_not_contending is not set, and
+ * will do nothing, so we are still safe.
+ */
+ if (hrtimer_try_to_cancel(&p->dl.inactive_timer) == 1)
+ put_task_struct(p);
+ }
+ raw_spin_unlock(&rq->lock);
+
out:
return cpu;
}
@@ -1743,16 +1860,25 @@ void __init init_sched_dl_class(void)
static void switched_from_dl(struct rq *rq, struct task_struct *p)
{
/*
- * Start the deadline timer; if we switch back to dl before this we'll
- * continue consuming our current CBS slice. If we stay outside of
- * SCHED_DEADLINE until the deadline passes, the timer will reset the
- * task.
+ * task_go_inactive() can start the "inactive timer" (if the 0-lag
+ * time is in the future). If the task switches back to dl before
+ * the "inactive timer" fires, it can continue to consume its current
+ * runtime using its current deadline. If it stays outside of
+ * SCHED_DEADLINE until the 0-lag time passes, inactive_task_timer()
+ * will reset the task parameters.
*/
- if (!start_dl_timer(p))
- __dl_clear_params(p);
+ if (task_on_rq_queued(p) && p->dl.dl_runtime)
+ task_go_inactive(p);
- if (task_on_rq_queued(p))
+ /*
+ * We cannot use inactive_task_timer() to invoke sub_running_bw()
+ * at the 0-lag time, because the task could have been migrated
+ * while SCHED_OTHER in the meanwhile.
+ */
+ if (p->dl.dl_non_contending) {
sub_running_bw(&p->dl, &rq->dl);
+ p->dl.dl_non_contending = 0;
+ }
/*
* Since this might be the only -deadline task on the rq,
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 0659772..e422803 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1367,6 +1367,7 @@ extern void init_rt_bandwidth(struct rt_bandwidth *rt_b,
u64 period, u64 runtime
extern struct dl_bandwidth def_dl_bandwidth;
extern void init_dl_bandwidth(struct dl_bandwidth *dl_b, u64 period, u64
runtime);
extern void init_dl_task_timer(struct sched_dl_entity *dl_se);
+extern void init_inactive_task_timer(struct sched_dl_entity *dl_se);
unsigned long to_ratio(u64 period, u64 runtime);
--
2.7.4
