sched/fair: Avoid a second scan of target in select_idle_cpu

gormanm · Peter Zijlstra · commit 56498cfb045d · 2021-08-04T15:16:44.000+02:00
When select_idle_cpu starts scanning for an idle CPU, it starts with a target CPU that has already been checked by select_idle_sibling. This patch starts with the next CPU instead. Signed-off-by: Mel Gorman <mgorman@techsingularity.net> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20210804115857.6253-3-mgorman@techsingularity.net
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
@@ -6220,7 +6220,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
 		time = cpu_clock(this);
 	}
 
-	for_each_cpu_wrap(cpu, cpus, target) {
+	for_each_cpu_wrap(cpu, cpus, target + 1) {
 		if (has_idle_core) {
 			i = select_idle_core(p, cpu, cpus, &idle_cpu);
 			if ((unsigned int)i < nr_cpumask_bits)

Original file line number	Diff line number	Diff line change
`@@ -6220,7 +6220,7 @@ static int select_idle_cpu(struct task_struct p, struct sched_domain sd, bool`
`6220`	`6220`	`time = cpu_clock(this);`
`6221`	`6221`	`}`
`6222`	`6222`
`6223`		`- for_each_cpu_wrap(cpu, cpus, target) {`
	`6223`	`+ for_each_cpu_wrap(cpu, cpus, target + 1) {`
`6224`	`6224`	`if (has_idle_core) {`
`6225`	`6225`	`i = select_idle_core(p, cpu, cpus, &idle_cpu);`
`6226`	`6226`	`if ((unsigned int)i < nr_cpumask_bits)`