[tip:sched/core] sched/fair: Update task group' s load_avg after task migration

[tip-bot for Yuyang Du <tipbot@zytor.com>]

Commit-ID:  3e386d56bafbb6d2540b49367444997fc671ea69
Gitweb:     http://git.kernel.org/tip/3e386d56bafbb6d2540b49367444997fc671ea69
Author:     Yuyang Du <yuyang.du@intel.com>
AuthorDate: Tue, 13 Oct 2015 09:18:23 +0800
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 20 Oct 2015 10:13:35 +0200

sched/fair: Update task group's load_avg after task migration

When cfs_rq has cfs_rq->removed_load_avg set (when a task migrates from
this cfs_rq), we need to update its contribution to the group's load_avg.

This should not increase tg's update too much, because in most cases, the
cfs_rq has already decayed its load_avg.

Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Yuyang Du <yuyang.du@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1444699103-20272-2-git-send-email-yuyang.du@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/fair.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bc62c50..9a5e60f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2664,13 +2664,14 @@ static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq);
 /* Group cfs_rq's load_avg is used for task_h_load and update_cfs_share */
 static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
 {
-	int decayed;
 	struct sched_avg *sa = &cfs_rq->avg;
+	int decayed, removed = 0;
 
 	if (atomic_long_read(&cfs_rq->removed_load_avg)) {
 		long r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
 		sa->load_avg = max_t(long, sa->load_avg - r, 0);
 		sa->load_sum = max_t(s64, sa->load_sum - r * LOAD_AVG_MAX, 0);
+		removed = 1;
 	}
 
 	if (atomic_long_read(&cfs_rq->removed_util_avg)) {
@@ -2688,7 +2689,7 @@ static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
 	cfs_rq->load_last_update_time_copy = sa->last_update_time;
 #endif
 
-	return decayed;
+	return decayed || removed;
 }
 
 /* Update task and its cfs_rq load average */