linux-kernel - [PATCH v5 3/3] sched/fair: Combine EAS check with overutilized access

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Message-Id: <20240306102454.341014-4-sshegde@linux.ibm.com>
Date: Wed,  6 Mar 2024 15:54:54 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: mingo@...nel.org, peterz@...radead.org, vincent.guittot@...aro.org
Cc: sshegde@...ux.ibm.com, yu.c.chen@...el.com, dietmar.eggemann@....com,
        linux-kernel@...r.kernel.org, nysal@...ux.ibm.com,
        aboorvad@...ux.ibm.com, srikar@...ux.ibm.com, vschneid@...hat.com,
        pierre.gondois@....com, qyousef@...alina.io
Subject: [PATCH v5 3/3] sched/fair: Combine EAS check with overutilized access

Access to overutilized is always used with sched_energy_enabled in
the pattern:

if (sched_energy_enabled && !overutilized)
       do something

So modify the helper function to return this pattern. This is more
readable code as it would say, do something when root domain is not
overutilized.

No change in functionality intended.

Suggested-by: Vincent Guittot <vincent.guittot@...aro.org>
Signed-off-by: Shrikanth Hegde <sshegde@...ux.ibm.com>
---
 kernel/sched/fair.c | 26 ++++++++++----------------
 1 file changed, 10 insertions(+), 16 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e3086c8930ea..62f247bdec86 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6676,12 +6676,11 @@ static inline bool cpu_overutilized(int cpu)
 }

 /*
- * Ensure that caller can do EAS. overutilized value
- * make sense only if EAS is enabled
+ * overutilized value make sense only if EAS is enabled
  */
-static inline int is_rd_overutilized(struct root_domain *rd)
+static inline int is_rd_not_overutilized(struct root_domain *rd)
 {
-	return READ_ONCE(rd->overutilized);
+	return sched_energy_enabled() && !READ_ONCE(rd->overutilized);
 }

 static inline void set_rd_overutilized_status(struct root_domain *rd,
@@ -6700,10 +6699,8 @@ static inline void check_update_overutilized_status(struct rq *rq)
 	 * overutilized field is used for load balancing decisions only
 	 * if energy aware scheduler is being used
 	 */
-	if (!sched_energy_enabled())
-		return;

-	if (!is_rd_overutilized(rq->rd) && cpu_overutilized(rq->cpu))
+	if (is_rd_not_overutilized(rq->rd) && cpu_overutilized(rq->cpu))
 		set_rd_overutilized_status(rq->rd, SG_OVERUTILIZED);
 }
 #else
@@ -6718,7 +6715,7 @@ static inline void set_rd_overutilized_status(struct root_domain *rd,
 	return 0;
 }

-static inline int is_rd_overutilized(struct root_domain *rd)
+static inline int is_rd_not_overutilized(struct root_domain *rd)
 {
 	return 0;
 }
@@ -8003,7 +8000,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)

 	rcu_read_lock();
 	pd = rcu_dereference(rd->pd);
-	if (!pd || is_rd_overutilized(rd))
+	if (!pd)
 		goto unlock;

 	/*
@@ -8206,7 +8203,7 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags)
 		    cpumask_test_cpu(cpu, p->cpus_ptr))
 			return cpu;

-		if (sched_energy_enabled()) {
+		if (is_rd_not_overutilized(this_rq()->rd)) {
 			new_cpu = find_energy_efficient_cpu(p, prev_cpu);
 			if (new_cpu >= 0)
 				return new_cpu;
@@ -10883,12 +10880,9 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
 	if (busiest->group_type == group_misfit_task)
 		goto force_balance;

-	if (sched_energy_enabled()) {
-		struct root_domain *rd = env->dst_rq->rd;
-
-		if (rcu_dereference(rd->pd) && !is_rd_overutilized(rd))
-			goto out_balanced;
-	}
+	if (is_rd_not_overutilized(env->dst_rq->rd) &&
+	    rcu_dereference(env->dst_rq->rd->pd))
+		goto out_balanced;

 	/* ASYM feature bypasses nice load balance check */
 	if (busiest->group_type == group_asym_packing)
--
2.39.3