sched/fair: Use load instead of runnable load in load_balance()

'runnable load' was originally introduced to take into account the case
where blocked load biases the load balance decision which was selecting
underutilized groups 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 wake up on the CPU.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Morten.Rasmussen@arm.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: hdanton@sina.com
Cc: parth@linux.ibm.com
Cc: pauld@redhat.com
Cc: quentin.perret@arm.com
Cc: riel@surriel.com
Cc: srikar@linux.vnet.ibm.com
Cc: valentin.schneider@arm.com
Link: https://lkml.kernel.org/r/1571405198-27570-7-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/fair.c

@@ -5375,6 +5375,11 @@ 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;
@@ -8049,7 +8054,7 @@ 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;
 
@@ -8507,7 +8512,7 @@ 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);
@@ -8667,22 +8672,21 @@ static struct rq *find_busiest_queue(struct lb_env *env,
 		switch (env->migration_type) {
 		case migrate_load:
 			/*
-			 * When comparing with load imbalance, use
-			 * cpu_runnable_load() which is not scaled with the CPU
-			 * capacity.
+			 * 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))
 				break;
 
 			/*
 			 * For the load comparisons with the other CPUs,
-			 * consider the cpu_runnable_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.
+			 * consider 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.
 			 *
 			 * Thus we're looking for max(load_i / capacity_i),
 			 * crosswise multiplication to rid ourselves of the