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

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Date:   Tue,  7 Aug 2018 17:56:27 +0200
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 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, 19 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5f1b6c6..ceb6bed 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8360,22 +8360,32 @@ static struct rq *find_busiest_queue(struct lb_env *env,
  */
 #define MAX_PINNED_INTERVAL	512
 
-static int need_active_balance(struct lb_env *env)
+static inline bool
+asym_active_balance(enum cpu_idle_type idle, unsigned int flags, int dst, int src)
 {
-	struct sched_domain *sd = env->sd;
-
-	if (env->idle != CPU_NOT_IDLE) {
+	if (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 ((flags & SD_ASYM_PACKING) &&
+		    sched_asym_prefer(dst, src))
+			return true;
 	}
 
+	return false;
+}
+
+static int need_active_balance(struct lb_env *env)
+{
+	struct sched_domain *sd = env->sd;
+
+
+	if (asym_active_balance(env->idle, sd->flags, env->dst_cpu, env->src_cpu))
+		return 1;
+
 	/*
 	 * The dst_cpu is idle and the src_cpu CPU has only 1 CFS task.
 	 * It's worth migrating the task if the src_cpu's capacity is reduced
@@ -8650,7 +8660,8 @@ 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.idle, sd->flags, env.dst_cpu, env.src_cpu)) {
 		/* We were unbalanced, so reset the balancing interval */
 		sd->balance_interval = sd->min_interval;
 	} else {
-- 
2.7.4