Re: A strange behavior of sched_fair

Kei Tokunaga
2008-02-29T20:23:19Z

Ingo Molnar wrote, (2008/02/29 14:42):
> * Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
>
>>> Seems the vruntime doesn't get re-set if you move tasks between
>>> groups. sched_move_task() should call place_entity() in the context
>>> of the new cfs_rq.
>> This should do I guess - uncompiled, untested
>
> if someone tests it and if it solves the problem i'll apply it to the
> scheduler tree.

Hi Ingo, Peter,

Thanks for the patch, Peter. I modified it a bit to compile and
confirmed the issue did not occur on my ia64 box. I am attaching
the revised patch below.

Thanks,
Kei

Subject: sched: fair-group: fixup tasks on group move

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.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

---

linux-2.6.25-rc3-cgroup-kei/include/linux/sched.h | 4 ++++
linux-2.6.25-rc3-cgroup-kei/kernel/sched.c | 3 +++
linux-2.6.25-rc3-cgroup-kei/kernel/sched_fair.c | 14 ++++++++++++++
3 files changed, 21 insertions(+)

diff -puN include/linux/sched.h~sched_fair include/linux/sched.h
--- linux-2.6.25-rc3-cgroup/include/linux/sched.h~sched_fair 2008-02-29 12:26:47.000000000 -0500
+++ linux-2.6.25-rc3-cgroup-kei/include/linux/sched.h 2008-02-29 12:26:47.000000000 -0500
@@ -898,6 +898,10 @@ 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 -puN kernel/sched.c~sched_fair kernel/sched.c
--- linux-2.6.25-rc3-cgroup/kernel/sched.c~sched_fair 2008-02-29 12:26:47.000000000 -0500
+++ linux-2.6.25-rc3-cgroup-kei/kernel/sched.c 2008-02-29 12:26:47.000000000 -0500
@@ -7825,6 +7825,9 @@ void sched_move_task(struct task_struct

set_task_rq(tsk, task_cpu(tsk));

+ if (tsk->sched_class->moved_group)
+ tsk->sched_class->moved_group(tsk);
+
if (on_rq) {
if (unlikely(running))
tsk->sched_class->set_curr_task(rq);
diff -puN kernel/sched_fair.c~sched_fair kernel/sched_fair.c
--- linux-2.6.25-rc3-cgroup/kernel/sched_fair.c~sched_fair 2008-02-29 12:26:47.000000000 -0500
+++ linux-2.6.25-rc3-cgroup-kei/kernel/sched_fair.c 2008-02-29 13:49:15.000000000 -0500
@@ -1403,6 +1403,16 @@ static void set_curr_task_fair(struct 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:
*/
@@ -1431,6 +1441,10 @@ static const struct sched_class fair_sch

.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

_