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From:   Yiwei Lin <s921975628@gmail.com>
To:     mingo@redhat.com, peterz@infradead.org
Cc:     vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        wuyun.abel@bytedance.com, linux-kernel@vger.kernel.org,
        s921975628@gmail.com
Subject: [PATCH v3 1/1] sched/fair: Track current se's EEVDF parameters
Date:   Sat,  4 Nov 2023 02:44:32 +0800
Message-Id: <20231103184432.9247-2-s921975628@gmail.com>
In-Reply-To: <20231103184432.9247-1-s921975628@gmail.com>
References: <20231103184432.9247-1-s921975628@gmail.com>
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Precedence: bulk

After dequeuing the current-picked scheduling entity with
`__dequeue_entity`, its contribution to the EEVDF parameters
cfs_rq->avg_vruntime and cfs_rq->avg_load are also removed.
Because these should in fact be considered for the EEVDF algorithm,
we took curr as the special case and inserted back the contributions
when requests for cfs_rq->avg_vruntime and cfs_rq->avg_load.

Functions like `entity_eligible` which is called inside a loop may
therefore recalculate these statistics repeatly and require more effort.
Instead, we could just avoid to remove these statistics from
cfs_rq->avg_vruntime and cfs_rq->avg_load directly.

Signed-off-by: Yiwei Lin <s921975628@gmail.com>
---
 kernel/sched/fair.c | 40 ++++++++++++----------------------------
 1 file changed, 12 insertions(+), 28 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 876798824..cb915fe42 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -655,17 +655,9 @@ void avg_vruntime_update(struct cfs_rq *cfs_rq, s64 delta)
  */
 u64 avg_vruntime(struct cfs_rq *cfs_rq)
 {
-	struct sched_entity *curr = cfs_rq->curr;
 	s64 avg = cfs_rq->avg_vruntime;
 	long load = cfs_rq->avg_load;
 
-	if (curr && curr->on_rq) {
-		unsigned long weight = scale_load_down(curr->load.weight);
-
-		avg += entity_key(cfs_rq, curr) * weight;
-		load += weight;
-	}
-
 	if (load) {
 		/* sign flips effective floor / ceil */
 		if (avg < 0)
@@ -722,17 +714,9 @@ static void update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se)
  */
 int entity_eligible(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	struct sched_entity *curr = cfs_rq->curr;
 	s64 avg = cfs_rq->avg_vruntime;
 	long load = cfs_rq->avg_load;
 
-	if (curr && curr->on_rq) {
-		unsigned long weight = scale_load_down(curr->load.weight);
-
-		avg += entity_key(cfs_rq, curr) * weight;
-		load += weight;
-	}
-
 	return avg >= entity_key(cfs_rq, se) * load;
 }
 
@@ -815,7 +799,6 @@ RB_DECLARE_CALLBACKS(static, min_deadline_cb, struct sched_entity,
  */
 static void __enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	avg_vruntime_add(cfs_rq, se);
 	se->min_deadline = se->deadline;
 	rb_add_augmented_cached(&se->run_node, &cfs_rq->tasks_timeline,
 				__entity_less, &min_deadline_cb);
@@ -825,7 +808,6 @@ static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	rb_erase_augmented_cached(&se->run_node, &cfs_rq->tasks_timeline,
 				  &min_deadline_cb);
-	avg_vruntime_sub(cfs_rq, se);
 }
 
 struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
@@ -1137,6 +1119,7 @@ static void update_curr(struct cfs_rq *cfs_rq)
 	struct sched_entity *curr = cfs_rq->curr;
 	u64 now = rq_clock_task(rq_of(cfs_rq));
 	u64 delta_exec;
+	u64 delta_fair;
 
 	if (unlikely(!curr))
 		return;
@@ -1158,7 +1141,9 @@ static void update_curr(struct cfs_rq *cfs_rq)
 	curr->sum_exec_runtime += delta_exec;
 	schedstat_add(cfs_rq->exec_clock, delta_exec);
 
-	curr->vruntime += calc_delta_fair(delta_exec, curr);
+	delta_fair = calc_delta_fair(delta_exec, curr);
+	curr->vruntime += delta_fair;
+	cfs_rq->avg_vruntime += delta_fair * scale_load_down(curr->load.weight);
 	update_deadline(cfs_rq, curr);
 	update_min_vruntime(cfs_rq);
 
@@ -3675,8 +3660,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
 		/* commit outstanding execution time */
 		if (cfs_rq->curr == se)
 			update_curr(cfs_rq);
-		else
-			avg_vruntime_sub(cfs_rq, se);
+		avg_vruntime_sub(cfs_rq, se);
 		update_load_sub(&cfs_rq->load, se->load.weight);
 	}
 	dequeue_load_avg(cfs_rq, se);
@@ -3712,8 +3696,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
 	enqueue_load_avg(cfs_rq, se);
 	if (se->on_rq) {
 		update_load_add(&cfs_rq->load, se->load.weight);
-		if (cfs_rq->curr != se)
-			avg_vruntime_add(cfs_rq, se);
+		avg_vruntime_add(cfs_rq, se);
 	}
 }
 
@@ -5023,7 +5006,6 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 	 * EEVDF: placement strategy #1 / #2
 	 */
 	if (sched_feat(PLACE_LAG) && cfs_rq->nr_running) {
-		struct sched_entity *curr = cfs_rq->curr;
 		unsigned long load;
 
 		lag = se->vlag;
@@ -5081,8 +5063,6 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 		 *   vl_i = (W + w_i)*vl'_i / W
 		 */
 		load = cfs_rq->avg_load;
-		if (curr && curr->on_rq)
-			load += scale_load_down(curr->load.weight);
 
 		lag *= load + scale_load_down(se->load.weight);
 		if (WARN_ON_ONCE(!load))
@@ -5158,8 +5138,10 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 
 	check_schedstat_required();
 	update_stats_enqueue_fair(cfs_rq, se, flags);
-	if (!curr)
+	if (!curr) {
+		avg_vruntime_add(cfs_rq, se);
 		__enqueue_entity(cfs_rq, se);
+	}
 	se->on_rq = 1;
 
 	if (cfs_rq->nr_running == 1) {
@@ -5228,8 +5210,10 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 	clear_buddies(cfs_rq, se);
 
 	update_entity_lag(cfs_rq, se);
-	if (se != cfs_rq->curr)
+	if (se != cfs_rq->curr) {
 		__dequeue_entity(cfs_rq, se);
+		avg_vruntime_sub(cfs_rq, se);
+	}
 	se->on_rq = 0;
 	account_entity_dequeue(cfs_rq, se);
 
-- 
2.34.1