[PATCH v3] sched/fair: fix unthrottle_cfs_rq for leaf_cfs_rq list

[PATCH v3] sched/fair: fix unthrottle_cfs_rq for leaf_cfs_rq list

[Vincent Guittot]

Although not exactly identical, unthrottle_cfs_rq() and enqueue_task_fair()
are quite close and follow the same sequence for enqueuing an entity in the
cfs hierarchy. Modify unthrottle_cfs_rq() to use the same pattern as
enqueue_task_fair(). This fixes a problem already faced with the latter and
add an optimization in the last for_each_sched_entity loop.

Reported-by Tao Zhou <zohooouoto@zoho.com.cn>
Reviewed-by: Phil Auld <pauld@redhat.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---

v3 changes:
  - remove the unused enqueue variable

 kernel/sched/fair.c | 42 ++++++++++++++++++++++++++++++------------
 1 file changed, 30 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4e12ba882663..9a58874ef104 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4792,7 +4792,6 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 	struct rq *rq = rq_of(cfs_rq);
 	struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
 	struct sched_entity *se;
-	int enqueue = 1;
 	long task_delta, idle_task_delta;
 
 	se = cfs_rq->tg->se[cpu_of(rq)];
@@ -4816,26 +4815,44 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 	idle_task_delta = cfs_rq->idle_h_nr_running;
 	for_each_sched_entity(se) {
 		if (se->on_rq)
-			enqueue = 0;
+			break;
+		cfs_rq = cfs_rq_of(se);
+		enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
 
+		cfs_rq->h_nr_running += task_delta;
+		cfs_rq->idle_h_nr_running += idle_task_delta;
+
+		/* end evaluation on encountering a throttled cfs_rq */
+		if (cfs_rq_throttled(cfs_rq))
+			goto unthrottle_throttle;
+	}
+
+	for_each_sched_entity(se) {
 		cfs_rq = cfs_rq_of(se);
-		if (enqueue) {
-			enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
-		} else {
-			update_load_avg(cfs_rq, se, 0);
-			se_update_runnable(se);
-		}
+
+		update_load_avg(cfs_rq, se, UPDATE_TG);
+		se_update_runnable(se);
 
 		cfs_rq->h_nr_running += task_delta;
 		cfs_rq->idle_h_nr_running += idle_task_delta;
 
+
+		/* end evaluation on encountering a throttled cfs_rq */
 		if (cfs_rq_throttled(cfs_rq))
-			break;
+			goto unthrottle_throttle;
+
+		/*
+		 * One parent has been throttled and cfs_rq removed from the
+		 * list. Add it back to not break the leaf list.
+		 */
+		if (throttled_hierarchy(cfs_rq))
+			list_add_leaf_cfs_rq(cfs_rq);
 	}
 
-	if (!se)
-		add_nr_running(rq, task_delta);
+	/* At this point se is NULL and we are at root level*/
+	add_nr_running(rq, task_delta);
 
+unthrottle_throttle:
 	/*
 	 * The cfs_rq_throttled() breaks in the above iteration can result in
 	 * incomplete leaf list maintenance, resulting in triggering the
@@ -4844,7 +4861,8 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 	for_each_sched_entity(se) {
 		cfs_rq = cfs_rq_of(se);
 
-		list_add_leaf_cfs_rq(cfs_rq);
+		if (list_add_leaf_cfs_rq(cfs_rq))
+			break;
 	}
 
 	assert_list_leaf_cfs_rq(rq);
-- 
2.17.1

Re: [PATCH v3] sched/fair: fix unthrottle_cfs_rq for leaf_cfs_rq list

[bsegall]

Vincent Guittot <vincent.guittot@linaro.org> writes:

> Although not exactly identical, unthrottle_cfs_rq() and enqueue_task_fair()
> are quite close and follow the same sequence for enqueuing an entity in the
> cfs hierarchy. Modify unthrottle_cfs_rq() to use the same pattern as
> enqueue_task_fair(). This fixes a problem already faced with the latter and
> add an optimization in the last for_each_sched_entity loop.
>
> Reported-by Tao Zhou <zohooouoto@zoho.com.cn>
> Reviewed-by: Phil Auld <pauld@redhat.com>

Reveiewed-by: Ben Segall <bsegall@google.com>

> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
>
> v3 changes:
>   - remove the unused enqueue variable
>
>  kernel/sched/fair.c | 42 ++++++++++++++++++++++++++++++------------
>  1 file changed, 30 insertions(+), 12 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 4e12ba882663..9a58874ef104 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4792,7 +4792,6 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
>  	struct rq *rq = rq_of(cfs_rq);
>  	struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
>  	struct sched_entity *se;
> -	int enqueue = 1;
>  	long task_delta, idle_task_delta;
>  
>  	se = cfs_rq->tg->se[cpu_of(rq)];
> @@ -4816,26 +4815,44 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
>  	idle_task_delta = cfs_rq->idle_h_nr_running;
>  	for_each_sched_entity(se) {
>  		if (se->on_rq)
> -			enqueue = 0;
> +			break;
> +		cfs_rq = cfs_rq_of(se);
> +		enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
>  
> +		cfs_rq->h_nr_running += task_delta;
> +		cfs_rq->idle_h_nr_running += idle_task_delta;
> +
> +		/* end evaluation on encountering a throttled cfs_rq */
> +		if (cfs_rq_throttled(cfs_rq))
> +			goto unthrottle_throttle;
> +	}
> +
> +	for_each_sched_entity(se) {
>  		cfs_rq = cfs_rq_of(se);
> -		if (enqueue) {
> -			enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
> -		} else {
> -			update_load_avg(cfs_rq, se, 0);
> -			se_update_runnable(se);
> -		}
> +
> +		update_load_avg(cfs_rq, se, UPDATE_TG);
> +		se_update_runnable(se);
>  
>  		cfs_rq->h_nr_running += task_delta;
>  		cfs_rq->idle_h_nr_running += idle_task_delta;
>  
> +
> +		/* end evaluation on encountering a throttled cfs_rq */
>  		if (cfs_rq_throttled(cfs_rq))
> -			break;
> +			goto unthrottle_throttle;
> +
> +		/*
> +		 * One parent has been throttled and cfs_rq removed from the
> +		 * list. Add it back to not break the leaf list.
> +		 */
> +		if (throttled_hierarchy(cfs_rq))
> +			list_add_leaf_cfs_rq(cfs_rq);
>  	}
>  
> -	if (!se)
> -		add_nr_running(rq, task_delta);
> +	/* At this point se is NULL and we are at root level*/
> +	add_nr_running(rq, task_delta);
>  
> +unthrottle_throttle:
>  	/*
>  	 * The cfs_rq_throttled() breaks in the above iteration can result in
>  	 * incomplete leaf list maintenance, resulting in triggering the
> @@ -4844,7 +4861,8 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
>  	for_each_sched_entity(se) {
>  		cfs_rq = cfs_rq_of(se);
>  
> -		list_add_leaf_cfs_rq(cfs_rq);
> +		if (list_add_leaf_cfs_rq(cfs_rq))
> +			break;
>  	}
>  
>  	assert_list_leaf_cfs_rq(rq);

[tip: sched/urgent] sched/fair: Fix unthrottle_cfs_rq() for leaf_cfs_rq list

[tip-bot2 for Vincent Guittot]

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     39f23ce07b9355d05a64ae303ce20d1c4b92b957
Gitweb:        https://git.kernel.org/tip/39f23ce07b9355d05a64ae303ce20d1c4b92b957
Author:        Vincent Guittot <vincent.guittot@linaro.org>
AuthorDate:    Wed, 13 May 2020 15:55:28 +02:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 19 May 2020 20:34:10 +02:00

sched/fair: Fix unthrottle_cfs_rq() for leaf_cfs_rq list

Although not exactly identical, unthrottle_cfs_rq() and enqueue_task_fair()
are quite close and follow the same sequence for enqueuing an entity in the
cfs hierarchy. Modify unthrottle_cfs_rq() to use the same pattern as
enqueue_task_fair(). This fixes a problem already faced with the latter and
add an optimization in the last for_each_sched_entity loop.

Fixes: fe61468b2cb (sched/fair: Fix enqueue_task_fair warning)
Reported-by Tao Zhou <zohooouoto@zoho.com.cn>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Phil Auld <pauld@redhat.com>
Reviewed-by: Ben Segall <bsegall@google.com>
Link: https://lkml.kernel.org/r/20200513135528.4742-1-vincent.guittot@linaro.org
---
 kernel/sched/fair.c | 42 ++++++++++++++++++++++++++++++------------
 1 file changed, 30 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c6d57c3..538ba5d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4774,7 +4774,6 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 	struct rq *rq = rq_of(cfs_rq);
 	struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
 	struct sched_entity *se;
-	int enqueue = 1;
 	long task_delta, idle_task_delta;
 
 	se = cfs_rq->tg->se[cpu_of(rq)];
@@ -4798,26 +4797,44 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 	idle_task_delta = cfs_rq->idle_h_nr_running;
 	for_each_sched_entity(se) {
 		if (se->on_rq)
-			enqueue = 0;
+			break;
+		cfs_rq = cfs_rq_of(se);
+		enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
 
+		cfs_rq->h_nr_running += task_delta;
+		cfs_rq->idle_h_nr_running += idle_task_delta;
+
+		/* end evaluation on encountering a throttled cfs_rq */
+		if (cfs_rq_throttled(cfs_rq))
+			goto unthrottle_throttle;
+	}
+
+	for_each_sched_entity(se) {
 		cfs_rq = cfs_rq_of(se);
-		if (enqueue) {
-			enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
-		} else {
-			update_load_avg(cfs_rq, se, 0);
-			se_update_runnable(se);
-		}
+
+		update_load_avg(cfs_rq, se, UPDATE_TG);
+		se_update_runnable(se);
 
 		cfs_rq->h_nr_running += task_delta;
 		cfs_rq->idle_h_nr_running += idle_task_delta;
 
+
+		/* end evaluation on encountering a throttled cfs_rq */
 		if (cfs_rq_throttled(cfs_rq))
-			break;
+			goto unthrottle_throttle;
+
+		/*
+		 * One parent has been throttled and cfs_rq removed from the
+		 * list. Add it back to not break the leaf list.
+		 */
+		if (throttled_hierarchy(cfs_rq))
+			list_add_leaf_cfs_rq(cfs_rq);
 	}
 
-	if (!se)
-		add_nr_running(rq, task_delta);
+	/* At this point se is NULL and we are at root level*/
+	add_nr_running(rq, task_delta);
 
+unthrottle_throttle:
 	/*
 	 * The cfs_rq_throttled() breaks in the above iteration can result in
 	 * incomplete leaf list maintenance, resulting in triggering the
@@ -4826,7 +4843,8 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 	for_each_sched_entity(se) {
 		cfs_rq = cfs_rq_of(se);
 
-		list_add_leaf_cfs_rq(cfs_rq);
+		if (list_add_leaf_cfs_rq(cfs_rq))
+			break;
 	}
 
 	assert_list_leaf_cfs_rq(rq);