linux-kernel - [PATCH 2/2] sched/core: Optimize the order of scanning CPU

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Date:   Fri, 21 Oct 2022 14:15:58 +0800
From:   Hao Jia <jiahao.os@...edance.com>
To:     mingo@...hat.com, peterz@...radead.org, mingo@...nel.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        mgorman@...hsingularity.net
Cc:     linux-kernel@...r.kernel.org, Hao Jia <jiahao.os@...edance.com>
Subject: [PATCH 2/2] sched/core: Optimize the order of scanning CPU

When select_idle_capacity() starts scanning for an idle CPU, it starts
with target CPU that has already been checked in select_idle_sibling().
So, we finally try the target CPU. Similarly for task_numa_assign(),
we have just checked numa_migrate_on of dst_cpu, so start from the
next CPU. This also works for steal_cookie_task(), the first scan
must fail and start directly from the next one.

Signed-off-by: Hao Jia <jiahao.os@...edance.com>
---
 kernel/sched/core.c | 2 +-
 kernel/sched/fair.c | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5800b0623ff3..f6ad68714546 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6154,7 +6154,7 @@ static bool steal_cookie_task(int cpu, struct sched_domain *sd)
 {
 	int i;
 
-	for_each_cpu_wrap(i, sched_domain_span(sd), cpu) {
+	for_each_cpu_wrap(i, sched_domain_span(sd), cpu + 1) {
 		if (i == cpu)
 			continue;
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b7cbec539c77..d95ee285734e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1824,7 +1824,7 @@ static void task_numa_assign(struct task_numa_env *env,
 		int start = env->dst_cpu;
 
 		/* Find alternative idle CPU. */
-		for_each_cpu_wrap(cpu, cpumask_of_node(env->dst_nid), start) {
+		for_each_cpu_wrap(cpu, cpumask_of_node(env->dst_nid), start + 1) {
 			if (cpu == env->best_cpu || !idle_cpu(cpu) ||
 			    !cpumask_test_cpu(cpu, env->p->cpus_ptr)) {
 				continue;
@@ -6663,7 +6663,7 @@ select_idle_capacity(struct task_struct *p, struct sched_domain *sd, int target)
 
 	task_util = uclamp_task_util(p);
 
-	for_each_cpu_wrap(cpu, cpus, target) {
+	for_each_cpu_wrap(cpu, cpus, target + 1) {
 		unsigned long cpu_cap = capacity_of(cpu);
 
 		if (!available_idle_cpu(cpu) && !sched_idle_cpu(cpu))
-- 
2.37.0