linux-kernel - [PATCH v3 06/10] sched/fair: use load instead of runnable load in load

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Date:   Thu, 19 Sep 2019 09:33:37 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        peterz@...radead.org
Cc:     pauld@...hat.com, valentin.schneider@....com,
        srikar@...ux.vnet.ibm.com, quentin.perret@....com,
        dietmar.eggemann@....com, Morten.Rasmussen@....com,
        hdanton@...a.com, Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH v3 06/10] sched/fair: use load instead of runnable load in load_balance

runnable load has been introduced to take into account the case
where blocked load biases the load balance decision which was selecting
underutilized group with huge blocked load whereas other groups were
overloaded.

The load is now only used when groups are overloaded. In this case,
it's worth being conservative and taking into account the sleeping
tasks that might wakeup on the cpu.

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/fair.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7e74836..15ec38c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5385,6 +5385,11 @@ static unsigned long cpu_runnable_load(struct rq *rq)
 	return cfs_rq_runnable_load_avg(&rq->cfs);
 }
 
+static unsigned long cpu_load(struct rq *rq)
+{
+	return cfs_rq_load_avg(&rq->cfs);
+}
+
 static unsigned long capacity_of(int cpu)
 {
 	return cpu_rq(cpu)->cpu_capacity;
@@ -8070,7 +8075,7 @@ static inline void update_sg_lb_stats(struct lb_env *env,
 		if ((env->flags & LBF_NOHZ_STATS) && update_nohz_stats(rq, false))
 			env->flags |= LBF_NOHZ_AGAIN;
 
-		sgs->group_load += cpu_runnable_load(rq);
+		sgs->group_load += cpu_load(rq);
 		sgs->group_util += cpu_util(i);
 		sgs->sum_h_nr_running += rq->cfs.h_nr_running;
 
@@ -8512,7 +8517,7 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
 	init_sd_lb_stats(&sds);
 
 	/*
-	 * Compute the various statistics relavent for load balancing at
+	 * Compute the various statistics relevant for load balancing at
 	 * this level.
 	 */
 	update_sd_lb_stats(env, &sds);
@@ -8672,10 +8677,10 @@ static struct rq *find_busiest_queue(struct lb_env *env,
 		switch (env->balance_type) {
 		case migrate_load:
 			/*
-			 * When comparing with load imbalance, use cpu_runnable_load()
+			 * When comparing with load imbalance, use cpu_load()
 			 * which is not scaled with the CPU capacity.
 			 */
-			load = cpu_runnable_load(rq);
+			load = cpu_load(rq);
 
 			if (nr_running == 1 && load > env->imbalance &&
 			    !check_cpu_capacity(rq, env->sd))
@@ -8683,7 +8688,7 @@ static struct rq *find_busiest_queue(struct lb_env *env,
 
 			/*
 			 * For the load comparisons with the other CPU's, consider
-			 * the cpu_runnable_load() scaled with the CPU capacity, so
+			 * the cpu_load() scaled with the CPU capacity, so
 			 * that the load can be moved away from the CPU that is
 			 * potentially running at a lower capacity.
 			 *
-- 
2.7.4