linux-kernel - [PATCH v2 05/10] sched/fair: Hoist idle_stamp up from idle

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Message-Id: <1541448489-19692-6-git-send-email-steven.sistare@oracle.com>
Date:   Mon,  5 Nov 2018 12:08:04 -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 05/10] sched/fair: Hoist idle_stamp up from idle_balance

Move the update of idle_stamp from idle_balance to the call site in
pick_next_task_fair, to prepare for a future patch that adds work to
pick_next_task_fair which must be included in the idle_stamp interval.
No functional change.

Signed-off-by: Steve Sistare <steven.sistare@...cle.com>
---
 kernel/sched/fair.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c623338..305edf8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3724,6 +3724,8 @@ static inline bool within_margin(int value, int margin)
 	WRITE_ONCE(p->se.avg.util_est, ue);
 }
 
+#define IF_SMP(statement)	statement
+
 static void overload_clear(struct rq *rq)
 {
 	struct sparsemask *overload_cpus;
@@ -3769,6 +3771,8 @@ static inline int idle_balance(struct rq *rq, struct rq_flags *rf)
 	return 0;
 }
 
+#define IF_SMP(statement)	/* empty */
+
 static inline void overload_clear(struct rq *rq) {}
 static inline void overload_set(struct rq *rq) {}
 
@@ -6740,8 +6744,17 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
 	return p;
 
 idle:
+	/*
+	 * We must set idle_stamp _before_ calling idle_balance(), such that we
+	 * measure the duration of idle_balance() as idle time.
+	 */
+	IF_SMP(rq->idle_stamp = rq_clock(rq);)
+
 	new_tasks = idle_balance(rq, rf);
 
+	if (new_tasks)
+		IF_SMP(rq->idle_stamp = 0;)
+
 	/*
 	 * Because idle_balance() releases (and re-acquires) rq->lock, it is
 	 * possible for any higher priority task to appear. In that case we
@@ -9504,12 +9517,6 @@ static int idle_balance(struct rq *this_rq, struct rq_flags *rf)
 	u64 curr_cost = 0;
 
 	/*
-	 * We must set idle_stamp _before_ calling idle_balance(), such that we
-	 * measure the duration of idle_balance() as idle time.
-	 */
-	this_rq->idle_stamp = rq_clock(this_rq);
-
-	/*
 	 * Do not pull tasks towards !active CPUs...
 	 */
 	if (!cpu_active(this_cpu))
@@ -9600,9 +9607,6 @@ static int idle_balance(struct rq *this_rq, struct rq_flags *rf)
 	if (this_rq->nr_running != this_rq->cfs.h_nr_running)
 		pulled_task = -1;
 
-	if (pulled_task)
-		this_rq->idle_stamp = 0;
-
 	rq_repin_lock(this_rq, rf);
 
 	return pulled_task;
-- 
1.8.3.1