From bc3fae5a8ae7fd519f25a9e6fc4005c642a45892 Mon Sep 17 00:00:00 2001
From: Vincent Guittot <vincent.guittot@linaro.org>
Date: Wed, 15 Jan 2020 11:20:20 +0100
Subject: [PATCH] sched/fair: Remove redundant call to cpufreq_update_util()

References: bnc#1155798 (CPU scheduler functional and performance backports)
Patch-mainline: v5.6-rc1
Git-commit: a4f9a0e51bbf89cb461b1985a1a570e6b87da3b5

With commit

  bef69dd87828 ("sched/cpufreq: Move the cfs_rq_util_change() call to cpufreq_update_util()")

update_load_avg() has become the central point for calling cpufreq
(not including the update of blocked load). This change helps to
simplify further the number of calls to cpufreq_update_util() and to
remove last redundant ones. With update_load_avg(), we are now sure
that cpufreq_update_util() will be called after every task attachment
to a cfs_rq and especially after propagating this event down to the
util_avg of the root cfs_rq, which is the level that is used by
cpufreq governors like schedutil to set the frequency of a CPU.

The SCHED_CPUFREQ_MIGRATION flag forces an early call to cpufreq when
the migration happens in a cgroup whereas util_avg of root cfs_rq is
not yet updated and this call is duplicated with the one that happens
immediately after when the migration event reaches the root cfs_rq.
The dedicated flag SCHED_CPUFREQ_MIGRATION is now useless and can be
removed. The interface of attach_entity_load_avg() can also be
simplified accordingly.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lkml.kernel.org/r/1579083620-24943-1-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 include/linux/sched/cpufreq.h |    1 -
 kernel/sched/fair.c           |   14 +++++++-------
 2 files changed, 7 insertions(+), 8 deletions(-)

--- a/include/linux/sched/cpufreq.h
+++ b/include/linux/sched/cpufreq.h
@@ -9,7 +9,6 @@
  */
 
 #define SCHED_CPUFREQ_IOWAIT	(1U << 0)
-#define SCHED_CPUFREQ_MIGRATION	(1U << 1)
 
 #ifdef CONFIG_CPU_FREQ
 struct cpufreq_policy;
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -802,7 +802,7 @@ void post_init_entity_util_avg(struct ta
 		 * For !fair tasks do:
 		 *
 		update_cfs_rq_load_avg(now, cfs_rq);
-		attach_entity_load_avg(cfs_rq, se, 0);
+		attach_entity_load_avg(cfs_rq, se);
 		switched_from_fair(rq, p);
 		 *
 		 * such that the next switched_to_fair() has the
@@ -3115,7 +3115,7 @@ static inline void cfs_rq_util_change(st
 {
 	struct rq *rq = rq_of(cfs_rq);
 
-	if (&rq->cfs == cfs_rq || (flags & SCHED_CPUFREQ_MIGRATION)) {
+	if (&rq->cfs == cfs_rq) {
 		/*
 		 * There are a few boundary cases this might miss but it should
 		 * get called often enough that that should (hopefully) not be
@@ -3522,7 +3522,7 @@ update_cfs_rq_load_avg(u64 now, struct c
  * 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, int flags)
+static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	u32 divider = LOAD_AVG_MAX - 1024 + cfs_rq->avg.period_contrib;
 
@@ -3558,7 +3558,7 @@ static void attach_entity_load_avg(struc
 
 	add_tg_cfs_propagate(cfs_rq, se->avg.load_sum);
 
-	cfs_rq_util_change(cfs_rq, flags);
+	cfs_rq_util_change(cfs_rq, 0);
 
 	trace_pelt_cfs_tp(cfs_rq);
 }
@@ -3616,7 +3616,7 @@ static inline void update_load_avg(struc
 		 *
 		 * IOW we're enqueueing a task on a new CPU.
 		 */
-		attach_entity_load_avg(cfs_rq, se, SCHED_CPUFREQ_MIGRATION);
+		attach_entity_load_avg(cfs_rq, se);
 		update_tg_load_avg(cfs_rq, 0);
 
 	} else if (decayed) {
@@ -3859,7 +3859,7 @@ static inline void update_load_avg(struc
 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, int flags) {}
+attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
 static inline void
 detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
 
@@ -10430,7 +10430,7 @@ static void attach_entity_cfs_rq(struct
 
 	/* 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, 0);
+	attach_entity_load_avg(cfs_rq, se);
 	update_tg_load_avg(cfs_rq, false);
 	propagate_entity_cfs_rq(se);
 }