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SubjectRe: broken behavior in cfs when moving threads between cgroups
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On Wed, 2010-09-29 at 04:53 +0200, Mike Galbraith wrote:

> ..but, as you noted, moving out then _back_ at forced 0 lag would result
> in bogus vruntime deltas, so lag must be preserved. The sleeper's
> vruntime has to be set to relative before it's cfs_rq is changed, then
> back to absolute in moved_group_fair() I suppose.

I bent it up like so.

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 53eb33c..d2b06a9 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1073,7 +1073,7 @@ struct sched_class {
struct task_struct *task);

#ifdef CONFIG_FAIR_GROUP_SCHED
- void (*moved_group) (struct task_struct *p, int on_rq);
+ void (*moved_group) (struct task_struct *p, int on_rq, int leaving);
#endif
};

diff --git a/kernel/sched.c b/kernel/sched.c
index 1ab8394..7001d5a 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -8358,11 +8358,16 @@ void sched_move_task(struct task_struct *tsk)
if (unlikely(running))
tsk->sched_class->put_prev_task(rq, tsk);

+#ifdef CONFIG_FAIR_GROUP_SCHED
+ if (tsk->sched_class->moved_group)
+ tsk->sched_class->moved_group(tsk, on_rq, 1);
+#endif
+
set_task_rq(tsk, task_cpu(tsk));

#ifdef CONFIG_FAIR_GROUP_SCHED
if (tsk->sched_class->moved_group)
- tsk->sched_class->moved_group(tsk, on_rq);
+ tsk->sched_class->moved_group(tsk, on_rq, 0);
#endif

if (unlikely(running))
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 9b5b4f8..81885ae 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -3824,13 +3824,23 @@ static void set_curr_task_fair(struct rq *rq)
}

#ifdef CONFIG_FAIR_GROUP_SCHED
-static void moved_group_fair(struct task_struct *p, int on_rq)
+static void moved_group_fair(struct task_struct *p, int on_rq, int leaving)
{
struct cfs_rq *cfs_rq = task_cfs_rq(p);

update_curr(cfs_rq);
- if (!on_rq)
- place_entity(cfs_rq, &p->se, 1);
+
+ /*
+ * For runnable tasks, vruntime normalization is handled globally by
+ * dequeue_entity(). task_waking_fair() normalizes sleepers in the
+ * wakeup path (to allow lag to grow while sleeping), so we have to
+ * normalize before the task exits it's old cfs_rq, and prepare for
+ * the impending normalization before that happens.
+ */
+ if (!on_rq && leaving)
+ p->se.vruntime -= cfs_rq->min_vruntime;
+ else if (!on_rq)
+ p->se.vruntime += cfs_rq->min_vruntime;
}
#endif




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