[tip:sched/core] sched/fair: Fix sched_entity::avg:: decay_count initialization

[tip-bot for Kirill Tkhai <tipbot@zytor.com>]

Commit-ID:  bb04159df99fa353d0fb524574aca03ce2c6515b
Gitweb:     http://git.kernel.org/tip/bb04159df99fa353d0fb524574aca03ce2c6515b
Author:     Kirill Tkhai <ktkhai@parallels.com>
AuthorDate: Mon, 15 Dec 2014 14:56:58 +0300
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 14 Jan 2015 13:34:16 +0100

sched/fair: Fix sched_entity::avg::decay_count initialization

Child has the same decay_count as parent. If it's not zero,
we add it to parent's cfs_rq->removed_load:

wake_up_new_task()->set_task_cpu()->migrate_task_rq_fair().

Child's load is a just garbade after copying of parent,
it hasn't been on cfs_rq yet, and it must not be added to
cfs_rq::removed_load in migrate_task_rq_fair().

The patch moves sched_entity::avg::decay_count intialization
in sched_fork(). So, migrate_task_rq_fair() does not change
removed_load.

Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ben Segall <bsegall@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1418644618.6074.13.camel@tkhai
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/core.c | 3 +++
 kernel/sched/fair.c | 1 -
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 816c172..95ac795 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1832,6 +1832,9 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
 	p->se.prev_sum_exec_runtime	= 0;
 	p->se.nr_migrations		= 0;
 	p->se.vruntime			= 0;
+#ifdef CONFIG_SMP
+	p->se.avg.decay_count		= 0;
+#endif
 	INIT_LIST_HEAD(&p->se.group_node);
 
 #ifdef CONFIG_SCHEDSTATS
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 97000a9..2a0b302 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -676,7 +676,6 @@ void init_task_runnable_average(struct task_struct *p)
 {
 	u32 slice;
 
-	p->se.avg.decay_count = 0;
 	slice = sched_slice(task_cfs_rq(p), &p->se) >> 10;
 	p->se.avg.runnable_avg_sum = slice;
 	p->se.avg.runnable_avg_period = slice;