linux-kernel - [PATCH v2 07/10] sched/fair: Provide can_migrate_task

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Date:   Mon,  5 Nov 2018 12:08:06 -0800
From:   Steve Sistare <steven.sistare@...cle.com>
To:     mingo@...hat.com, peterz@...radead.org
Cc:     subhra.mazumdar@...cle.com, dhaval.giani@...cle.com,
        daniel.m.jordan@...cle.com, pavel.tatashin@...rosoft.com,
        matt@...eblueprint.co.uk, umgwanakikbuti@...il.com,
        riel@...hat.com, jbacik@...com, juri.lelli@...hat.com,
        valentin.schneider@....com, vincent.guittot@...aro.org,
        quentin.perret@....com, steven.sistare@...cle.com,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 07/10] sched/fair: Provide can_migrate_task_llc

Define a simpler version of can_migrate_task called can_migrate_task_llc
which does not require a struct lb_env argument, and judges whether a
migration from one CPU to another within the same LLC should be allowed.

Signed-off-by: Steve Sistare <steven.sistare@...cle.com>
---
 kernel/sched/fair.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index eb6e6cd..6b08383 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7166,6 +7166,34 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
 }
 
 /*
+ * Return true if task @p can migrate from @rq to @dst_rq in the same LLC.
+ * No need to test for co-locality, and no need to test task_hot(), as sharing
+ * LLC provides cache warmth at that level.
+ */
+static bool
+can_migrate_task_llc(struct task_struct *p, struct rq *rq, struct rq *dst_rq)
+{
+	int dst_cpu = dst_rq->cpu;
+
+	lockdep_assert_held(&rq->lock);
+
+	if (throttled_lb_pair(task_group(p), cpu_of(rq), dst_cpu))
+		return false;
+
+	if (!cpumask_test_cpu(dst_cpu, &p->cpus_allowed)) {
+		schedstat_inc(p->se.statistics.nr_failed_migrations_affine);
+		return false;
+	}
+
+	if (task_running(rq, p)) {
+		schedstat_inc(p->se.statistics.nr_failed_migrations_running);
+		return false;
+	}
+
+	return true;
+}
+
+/*
  * detach_task() -- detach the task for the migration from @src_rq to @dst_cpu.
  */
 static void detach_task(struct task_struct *p, struct rq *src_rq, int dst_cpu)
-- 
1.8.3.1