linux-kernel - [PATCH v4 1/5] sched/fair: Remove redundant check in select_idle

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Date:   Wed,  7 Sep 2022 19:19:56 +0800
From:   Abel Wu <wuyun.abel@...edance.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Josh Don <joshdon@...gle.com>, Chen Yu <yu.c.chen@...el.com>,
        Yicong Yang <yangyicong@...wei.com>,
        linux-kernel@...r.kernel.org, Abel Wu <wuyun.abel@...edance.com>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH v4 1/5] sched/fair: Remove redundant check in select_idle_smt()

If two cpus share LLC cache, then the two cores they belong to
are also in the same LLC domain.

Signed-off-by: Abel Wu <wuyun.abel@...edance.com>
Reviewed-by: Josh Don <joshdon@...gle.com>
Acked-by: Mel Gorman <mgorman@...hsingularity.net>
---
 kernel/sched/fair.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index efceb670e755..9657c7de5f57 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6350,14 +6350,11 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
 /*
  * Scan the local SMT mask for idle CPUs.
  */
-static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
+static int select_idle_smt(struct task_struct *p, int target)
 {
 	int cpu;
 
-	for_each_cpu(cpu, cpu_smt_mask(target)) {
-		if (!cpumask_test_cpu(cpu, p->cpus_ptr) ||
-		    !cpumask_test_cpu(cpu, sched_domain_span(sd)))
-			continue;
+	for_each_cpu_and(cpu, cpu_smt_mask(target), p->cpus_ptr) {
 		if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
 			return cpu;
 	}
@@ -6381,7 +6378,7 @@ static inline int select_idle_core(struct task_struct *p, int core, struct cpuma
 	return __select_idle_cpu(core, p);
 }
 
-static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
+static inline int select_idle_smt(struct task_struct *p, int target)
 {
 	return -1;
 }
@@ -6615,7 +6612,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
 		has_idle_core = test_idle_cores(target, false);
 
 		if (!has_idle_core && cpus_share_cache(prev, target)) {
-			i = select_idle_smt(p, sd, prev);
+			i = select_idle_smt(p, prev);
 			if ((unsigned int)i < nr_cpumask_bits)
 				return i;
 		}
-- 
2.37.3