linux-kernel - [PATCH v2 3/3] sched/fair: fix unnecessary increase of balance interval

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Date:   Fri, 14 Dec 2018 17:01:57 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     peterz@...radead.org, mingo@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     valentin.schneider@....com, Morten.Rasmussen@....com,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH v2 3/3] sched/fair: fix unnecessary increase of balance interval

In case of active balance, we increase the balance interval to cover
pinned tasks cases not covered by all_pinned logic. Neverthless, the active
migration triggered by asym packing should be treated as the normal
unbalanced case and reset the interval to default value otherwise active
migration for asym_packing can be easily delayed for hundreds of ms
because of this all_pinned detection mecanism.

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/fair.c | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9591e7a..487287e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8857,21 +8857,24 @@ static struct rq *find_busiest_queue(struct lb_env *env,
  */
 #define MAX_PINNED_INTERVAL	512
 
+static inline bool
+asym_active_balance(struct lb_env *env)
+{
+	/*
+	 * ASYM_PACKING needs to force migrate tasks from busy but
+	 * lower priority CPUs in order to pack all tasks in the
+	 * highest priority CPUs.
+	 */
+	return env->idle != CPU_NOT_IDLE && (env->sd->flags & SD_ASYM_PACKING) &&
+	       sched_asym_prefer(env->dst_cpu, env->src_cpu);
+}
+
 static int need_active_balance(struct lb_env *env)
 {
 	struct sched_domain *sd = env->sd;
 
-	if (env->idle != CPU_NOT_IDLE) {
-
-		/*
-		 * ASYM_PACKING needs to force migrate tasks from busy but
-		 * lower priority CPUs in order to pack all tasks in the
-		 * highest priority CPUs.
-		 */
-		if ((sd->flags & SD_ASYM_PACKING) &&
-		    sched_asym_prefer(env->dst_cpu, env->src_cpu))
-			return 1;
-	}
+	if (asym_active_balance(env))
+		return 1;
 
 	/*
 	 * The dst_cpu is idle and the src_cpu CPU has only 1 CFS task.
@@ -9150,7 +9153,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
 	} else
 		sd->nr_balance_failed = 0;
 
-	if (likely(!active_balance)) {
+	if (likely(!active_balance) || asym_active_balance(&env)) {
 		/* We were unbalanced, so reset the balancing interval */
 		sd->balance_interval = sd->min_interval;
 	} else {
-- 
2.7.4