sched/cpufreq: Provide migration hint

It was suggested that a migration hint might be usefull for the
CPU-freq governors.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/sched/cpufreq.h

@@ -9,6 +9,7 @@
  */
 
 #define SCHED_CPUFREQ_IOWAIT	(1U << 0)
+#define SCHED_CPUFREQ_MIGRATION	(1U << 1)
 
 #ifdef CONFIG_CPU_FREQ
 struct update_util_data {

kernel/sched/fair.c

@@ -772,7 +772,7 @@ void post_init_entity_util_avg(struct sched_entity *se)
 			 * For !fair tasks do:
 			 *
 			update_cfs_rq_load_avg(now, cfs_rq);
-			attach_entity_load_avg(cfs_rq, se);
+			attach_entity_load_avg(cfs_rq, se, 0);
 			switched_from_fair(rq, p);
 			 *
 			 * such that the next switched_to_fair() has the
@@ -3009,11 +3009,11 @@ static inline void update_cfs_group(struct sched_entity *se)
 }
 #endif /* CONFIG_FAIR_GROUP_SCHED */
 
-static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq)
+static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq, int flags)
 {
 	struct rq *rq = rq_of(cfs_rq);
 
-	if (&rq->cfs == cfs_rq) {
+	if (&rq->cfs == cfs_rq || (flags & SCHED_CPUFREQ_MIGRATION)) {
 		/*
 		 * There are a few boundary cases this might miss but it should
 		 * get called often enough that that should (hopefully) not be
@@ -3028,7 +3028,7 @@ static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq)
 		 *
 		 * See cpu_util().
 		 */
-		cpufreq_update_util(rq, 0);
+		cpufreq_update_util(rq, flags);
 	}
 }
 
@@ -3686,7 +3686,7 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
 #endif
 
 	if (decayed)
-		cfs_rq_util_change(cfs_rq);
+		cfs_rq_util_change(cfs_rq, 0);
 
 	return decayed;
 }
@@ -3699,7 +3699,7 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
  * Must call update_cfs_rq_load_avg() before this, since we rely on
  * cfs_rq->avg.last_update_time being current.
  */
-static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
+static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
 	u32 divider = LOAD_AVG_MAX - 1024 + cfs_rq->avg.period_contrib;
 
@@ -3735,7 +3735,7 @@ static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 
 	add_tg_cfs_propagate(cfs_rq, se->avg.load_sum);
 
-	cfs_rq_util_change(cfs_rq);
+	cfs_rq_util_change(cfs_rq, flags);
 }
 
 /**
@@ -3754,7 +3754,7 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 
 	add_tg_cfs_propagate(cfs_rq, -se->avg.load_sum);
 
-	cfs_rq_util_change(cfs_rq);
+	cfs_rq_util_change(cfs_rq, 0);
 }
 
 /*
@@ -3784,7 +3784,14 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 
 	if (!se->avg.last_update_time && (flags & DO_ATTACH)) {
 
-		attach_entity_load_avg(cfs_rq, se);
+		/*
+		 * DO_ATTACH means we're here from enqueue_entity().
+		 * !last_update_time means we've passed through
+		 * migrate_task_rq_fair() indicating we migrated.
+		 *
+		 * IOW we're enqueueing a task on a new CPU.
+		 */
+		attach_entity_load_avg(cfs_rq, se, SCHED_CPUFREQ_MIGRATION);
 		update_tg_load_avg(cfs_rq, 0);
 
 	} else if (decayed && (flags & UPDATE_TG))
@@ -3880,13 +3887,13 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
 
 static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int not_used1)
 {
-	cfs_rq_util_change(cfs_rq);
+	cfs_rq_util_change(cfs_rq, 0);
 }
 
 static inline void remove_entity_load_avg(struct sched_entity *se) {}
 
 static inline void
-attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
+attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) {}
 static inline void
 detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
 
@@ -9726,7 +9733,7 @@ static void attach_entity_cfs_rq(struct sched_entity *se)
 
 	/* Synchronize entity with its cfs_rq */
 	update_load_avg(cfs_rq, se, sched_feat(ATTACH_AGE_LOAD) ? 0 : SKIP_AGE_LOAD);
-	attach_entity_load_avg(cfs_rq, se);
+	attach_entity_load_avg(cfs_rq, se, 0);
 	update_tg_load_avg(cfs_rq, false);
 	propagate_entity_cfs_rq(se);
 }