linux-kernel - [RFC 1/8] Track the active utilisation

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Date:	Thu, 14 Jan 2016 16:24:46 +0100
From:	Luca Abeni <luca.abeni@...tn.it>
To:	linux-kernel@...r.kernel.org
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@....com>,
	Luca Abeni <luca.abeni@...tn.it>
Subject: [RFC 1/8] Track the active utilisation

The active utilisation here is defined as the total utilisation of the
active (TASK_RUNNING) tasks queued on a runqueue. Hence, it is increased
when a task wakes up and is decreased when a task blocks.
This might need to be fixed / improved by decreasing the active
utilisation at the so-called "0-lag time" instead of when the task blocks.

Signed-off-by: Juri Lelli <juri.lelli@....com>
---
 kernel/sched/deadline.c | 36 +++++++++++++++++++++++++++++++++++-
 kernel/sched/sched.h    |  5 +++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index cd64c97..e779cce 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -43,6 +43,24 @@ static inline int on_dl_rq(struct sched_dl_entity *dl_se)
 	return !RB_EMPTY_NODE(&dl_se->rb_node);
 }
 
+static void add_running_bw(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
+{
+	u64 se_bw = dl_se->dl_bw;
+
+	dl_rq->running_bw += se_bw;
+}
+
+static void clear_running_bw(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
+{
+	u64 se_bw = dl_se->dl_bw;
+
+	dl_rq->running_bw -= se_bw;
+	if (dl_rq->running_bw < 0) {
+		WARN_ON(1);
+		dl_rq->running_bw = 0;
+	}
+}
+
 static inline int is_leftmost(struct task_struct *p, struct dl_rq *dl_rq)
 {
 	struct sched_dl_entity *dl_se = &p->dl;
@@ -500,6 +518,8 @@ static void update_dl_entity(struct sched_dl_entity *dl_se,
 	struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
 	struct rq *rq = rq_of_dl_rq(dl_rq);
 
+	add_running_bw(dl_se, dl_rq);
+
 	/*
 	 * The arrival of a new instance needs special treatment, i.e.,
 	 * the actual scheduling parameters have to be "renewed".
@@ -961,8 +981,10 @@ static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
 	 * its rq, the bandwidth timer callback (which clearly has not
 	 * run yet) will take care of this.
 	 */
-	if (p->dl.dl_throttled && !(flags & ENQUEUE_REPLENISH))
+	if (p->dl.dl_throttled && !(flags & ENQUEUE_REPLENISH)) {
+		add_running_bw(&p->dl, &rq->dl);
 		return;
+	}
 
 	enqueue_dl_entity(&p->dl, pi_se, flags);
 
@@ -980,6 +1002,8 @@ static void dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags)
 {
 	update_curr_dl(rq);
 	__dequeue_task_dl(rq, p, flags);
+	if (flags & DEQUEUE_SLEEP)
+		clear_running_bw(&p->dl, &rq->dl);
 }
 
 /*
@@ -1218,6 +1242,8 @@ static void task_fork_dl(struct task_struct *p)
 static void task_dead_dl(struct task_struct *p)
 {
 	struct dl_bw *dl_b = dl_bw_of(task_cpu(p));
+	struct dl_rq *dl_rq = dl_rq_of_se(&p->dl);
+	struct rq *rq = rq_of_dl_rq(dl_rq);
 
 	/*
 	 * Since we are TASK_DEAD we won't slip out of the domain!
@@ -1226,6 +1252,10 @@ static void task_dead_dl(struct task_struct *p)
 	/* XXX we should retain the bw until 0-lag */
 	dl_b->total_bw -= p->dl.dl_bw;
 	raw_spin_unlock_irq(&dl_b->lock);
+
+	if (task_on_rq_queued(p)) {
+		clear_running_bw(&p->dl, &rq->dl);
+	}
 }
 
 static void set_curr_task_dl(struct rq *rq)
@@ -1705,6 +1735,10 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
 	if (!start_dl_timer(p))
 		__dl_clear_params(p);
 
+	if (task_on_rq_queued(p)) {
+		clear_running_bw(&p->dl, &rq->dl);
+	}
+
 	/*
 	 * Since this might be the only -deadline task on the rq,
 	 * this is the right place to try to pull some other one
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 10f1637..826ca6a 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -519,6 +519,11 @@ struct dl_rq {
 #else
 	struct dl_bw dl_bw;
 #endif
+	/* This is the "active utilization" for this runqueue.
+	 * Increased when a task wakes up (becomes TASK_RUNNING)
+	 * and decreased when a task blocks
+	 */
+	s64 running_bw;
 };
 
 #ifdef CONFIG_SMP
-- 
1.9.1