linux-kernel - [PATCH v3 2/3] sched: factor out the code getting cfs_rq's last_update

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Message-ID: <1444899676-5852-3-git-send-email-byungchul.park@lge.com>
Date:	Thu, 15 Oct 2015 18:01:15 +0900
From:	<byungchul.park@....com>
To:	mingo@...nel.org, peterz@...radead.org
CC:	linux-kernel@...r.kernel.org, yuyang.du@...el.com, pjt@...gle.com,
	efault@....de, tglx@...utronix.de,
	Byungchul Park <byungchul.park@....com>
Subject: [PATCH v3 2/3] sched: factor out the code getting cfs_rq's last_update_time

From: Byungchul Park <byungchul.park@....com>

In the case that rq->lock may not be held, care must be taken to get a
cfs_rq's last_update_time instead of just reading the variable. Since
it can happen at serveral places in the code in future, this patch
factors it out to a helper function.

Signed-off-by: Byungchul Park <byungchul.park@....com>
---
 kernel/sched/fair.c |   20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0f76903..08589a0 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2809,15 +2809,10 @@ dequeue_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 		max_t(s64,  cfs_rq->runnable_load_sum - se->avg.load_sum, 0);
 }
 
-/*
- * Task first catches up with cfs_rq, and then subtract
- * itself from the cfs_rq (task must be off the queue now).
- */
-void remove_entity_load_avg(struct sched_entity *se)
+/* This function is useful for the case that rq->lock may not be held */
+static inline u64 get_last_update_time(struct cfs_rq *cfs_rq)
 {
-	struct cfs_rq *cfs_rq = cfs_rq_of(se);
 	u64 last_update_time;
-
 #ifndef CONFIG_64BIT
 	u64 last_update_time_copy;
 
@@ -2829,6 +2824,17 @@ void remove_entity_load_avg(struct sched_entity *se)
 #else
 	last_update_time = cfs_rq->avg.last_update_time;
 #endif
+	return last_update_time;
+}
+
+/*
+ * Task first catches up with cfs_rq, and then subtract
+ * itself from the cfs_rq (task must be off the queue now).
+ */
+void remove_entity_load_avg(struct sched_entity *se)
+{
+	struct cfs_rq *cfs_rq = cfs_rq_of(se);
+	u64 last_update_time = get_last_update_time(cfs_rq);
 
 	__update_load_avg(last_update_time, cpu_of(rq_of(cfs_rq)), &se->avg, 0, 0, NULL);
 	atomic_long_add(se->avg.load_avg, &cfs_rq->removed_load_avg);
-- 
1.7.9.5

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