linux-kernel - [PATCH 06/10] sched/fair: Clear the target CPU from the cpumask of CPUs searched

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Date:   Thu,  3 Dec 2020 14:11:20 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Aubrey Li <aubrey.li@...ux.intel.com>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Ziljstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Linux-ARM <linux-arm-kernel@...ts.infradead.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 06/10] sched/fair: Clear the target CPU from the cpumask of CPUs searched

The target CPU is definitely not idle in both select_idle_core and
select_idle_cpu. For select_idle_core(), the SMT is potentially
checked unnecessarily as the core is definitely not idle if the
target is busy. For select_idle_cpu(), the first CPU checked is
simply a waste.

Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
---
 kernel/sched/fair.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 68dd9cd62fbd..1d8f5c4b4936 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6077,6 +6077,7 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int
 		return -1;
 
 	cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
+	__cpumask_clear_cpu(target, cpus);
 
 	for_each_cpu_wrap(core, cpus, target) {
 		bool idle = true;
@@ -6181,6 +6182,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
 	time = cpu_clock(this);
 
 	cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
+	__cpumask_clear_cpu(target, cpus);
 
 	for_each_cpu_wrap(cpu, cpus, target) {
 		schedstat_inc(this_rq()->sis_scanned);
-- 
2.26.2