[RFC][PATCH 2/4] sched: Make sched_class::set_cpus_allowed() unconditional

[Peter Zijlstra]

Give every class a set_cpus_allowed() method, this enables some small
optimization in the rt,dl implementation by avoiding a double
cpumask_weight() call.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 kernel/sched/core.c      |   17 +++++++++++------
 kernel/sched/deadline.c  |   20 ++++++++++++--------
 kernel/sched/fair.c      |    1 +
 kernel/sched/idle_task.c |    1 +
 kernel/sched/rt.c        |   12 ++++++++----
 kernel/sched/sched.h     |    2 ++
 kernel/sched/stop_task.c |    1 +
 7 files changed, 36 insertions(+), 18 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4791,17 +4791,22 @@ static struct rq *move_queued_task(struc
 	return rq;
 }
 
-void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
+/*
+ * sched_class::set_cpus_allowed must do the below, but is not required to
+ * actually call this function.
+ */
+void set_cpus_allowed_common(struct task_struct *p, const struct cpumask *new_mask)
 {
-	lockdep_assert_held(&p->pi_lock);
-
-	if (p->sched_class->set_cpus_allowed)
-		p->sched_class->set_cpus_allowed(p, new_mask);
-
 	cpumask_copy(&p->cpus_allowed, new_mask);
 	p->nr_cpus_allowed = cpumask_weight(new_mask);
 }
 
+void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
+{
+	lockdep_assert_held(&p->pi_lock);
+	p->sched_class->set_cpus_allowed(p, new_mask);
+}
+
 /*
  * This is how migration works:
  *
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1597,13 +1597,6 @@ static void set_cpus_allowed_dl(struct t
 		raw_spin_unlock(&src_dl_b->lock);
 	}
 
-	/*
-	 * Update only if the task is actually running (i.e.,
-	 * it is on the rq AND it is not throttled).
-	 */
-	if (!on_dl_rq(&p->dl))
-		return;
-
 	weight = cpumask_weight(new_mask);
 
 	/*
@@ -1611,7 +1604,14 @@ static void set_cpus_allowed_dl(struct t
 	 * can migrate or not.
 	 */
 	if ((p->nr_cpus_allowed > 1) == (weight > 1))
-		return;
+		goto done;
+
+	/*
+	 * Update only if the task is actually running (i.e.,
+	 * it is on the rq AND it is not throttled).
+	 */
+	if (!on_dl_rq(&p->dl))
+		goto done;
 
 	/*
 	 * The process used to be able to migrate OR it can now migrate
@@ -1628,6 +1628,10 @@ static void set_cpus_allowed_dl(struct t
 	}
 
 	update_dl_migration(&rq->dl);
+
+done:
+	cpumask_copy(&p->cpus_allowed, new_mask);
+	p->nr_cpus_allowed = weight;
 }
 
 /* Assumes rq->lock is held */
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8406,6 +8406,7 @@ const struct sched_class fair_sched_clas
 	.rq_offline		= rq_offline_fair,
 
 	.task_waking		= task_waking_fair,
+	.set_cpus_allowed	= set_cpus_allowed_common,
 #endif
 
 	.set_curr_task          = set_curr_task_fair,
--- a/kernel/sched/idle_task.c
+++ b/kernel/sched/idle_task.c
@@ -96,6 +96,7 @@ const struct sched_class idle_sched_clas
 
 #ifdef CONFIG_SMP
 	.select_task_rq		= select_task_rq_idle,
+	.set_cpus_allowed	= set_cpus_allowed_common,
 #endif
 
 	.set_curr_task          = set_curr_task_idle,
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2065,9 +2065,6 @@ static void set_cpus_allowed_rt(struct t
 
 	BUG_ON(!rt_task(p));
 
-	if (!task_on_rq_queued(p))
-		return;
-
 	weight = cpumask_weight(new_mask);
 
 	/*
@@ -2075,7 +2072,10 @@ static void set_cpus_allowed_rt(struct t
 	 * can migrate or not.
 	 */
 	if ((p->nr_cpus_allowed > 1) == (weight > 1))
-		return;
+		goto done;
+
+	if (!task_on_rq_queued(p))
+		goto done;
 
 	rq = task_rq(p);
 
@@ -2094,6 +2094,10 @@ static void set_cpus_allowed_rt(struct t
 	}
 
 	update_rt_migration(&rq->rt);
+
+done:
+	cpumask_copy(&p->cpus_allowed, new_mask);
+	p->nr_cpus_allowed = weight;
 }
 
 /* Assumes rq->lock is held */
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1252,6 +1252,8 @@ extern void trigger_load_balance(struct
 extern void idle_enter_fair(struct rq *this_rq);
 extern void idle_exit_fair(struct rq *this_rq);
 
+extern void set_cpus_allowed_common(struct task_struct *p, const struct cpumask *new_mask);
+
 #else
 
 static inline void idle_enter_fair(struct rq *rq) { }
--- a/kernel/sched/stop_task.c
+++ b/kernel/sched/stop_task.c
@@ -123,6 +123,7 @@ const struct sched_class stop_sched_clas
 
 #ifdef CONFIG_SMP
 	.select_task_rq		= select_task_rq_stop,
+	.set_cpus_allowed	= set_cpus_allowed_common,
 #endif
 
 	.set_curr_task          = set_curr_task_stop,


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