sched: retain vruntime

Kei Tokunaga reported an interactivity problem when moving tasks
between control groups.

Tasks would retain their old vruntime when moved between groups, this
can cause funny lags. Re-set the vruntime on group move to fit within
the new tree.

Reported-by: Kei Tokunaga <tokunaga.keiich@jp.fujitsu.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 23 insertions, 0 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 9ae4030067a9..11d8e9a74eff 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -899,6 +899,10 @@ struct sched_class {
                              int running);
         void (*prio_changed) (struct rq *this_rq, struct task_struct *task,
                              int oldprio, int running);
+
+#ifdef CONFIG_FAIR_GROUP_SCHED
+        void (*moved_group) (struct task_struct *p);
+#endif
 };
 
 struct load_weight {
diff --git a/kernel/sched.c b/kernel/sched.c
index dcd553cc4ee8..0b949c4e73ad 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -7625,6 +7625,11 @@ void sched_move_task(struct task_struct *tsk)
 
         set_task_rq(tsk, task_cpu(tsk));
 
+#ifdef CONFIG_FAIR_GROUP_SCHED
+        if (tsk->sched_class->moved_group)
+                tsk->sched_class->moved_group(tsk);
+#endif
+
         if (on_rq) {
                 if (unlikely(running))
                         tsk->sched_class->set_curr_task(rq);
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 3df4d46994ca..e2a530515619 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1353,6 +1353,16 @@ static void set_curr_task_fair(struct rq *rq)
                 set_next_entity(cfs_rq_of(se), se);
 }
 
+#ifdef CONFIG_FAIR_GROUP_SCHED
+static void moved_group_fair(struct task_struct *p)
+{
+        struct cfs_rq *cfs_rq = task_cfs_rq(p);
+
+        update_curr(cfs_rq);
+        place_entity(cfs_rq, &p->se, 1);
+}
+#endif
+
 /*
  * All the scheduling class methods:
  */
@@ -1381,6 +1391,10 @@ static const struct sched_class fair_sched_class = {
 
         .prio_changed           = prio_changed_fair,
         .switched_to            = switched_to_fair,
+
+#ifdef CONFIG_FAIR_GROUP_SCHED
+        .moved_group            = moved_group_fair,
+#endif
 };
 
 #ifdef CONFIG_SCHED_DEBUG