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>

2 files changed, 3 insertions, 1 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 816c17203c16..95ac795ab3d3 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 97000a99a293..2a0b302e51de 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;