[PATCH v3] sched: sync with the prev cfs when changing cgroup within a cpu

[PATCH v3] sched: sync with the prev cfs when changing cgroup within a cpu

[byungchul.park]

From: Byungchul Park <byungchul.park@lge.com>

change from v2 to v3
* rebase to tip git

change from v1 to v2
* use #ifdef CONFIG_SMP to load tracking code
* make commit message compact which made confused

----->8-----
>From 31c4509d09cd43bf52c12ef85716aa4c3b729b57 Mon Sep 17 00:00:00 2001
From: Byungchul Park <byungchul.park@lge.com>
Date: Wed, 12 Aug 2015 15:51:21 +0900
Subject: [PATCH v3] sched: sync with the prev cfs when changing cgroup within
 a cpu

current code seems to be wrong with cfs_rq's avg loads when changing
a task's cgroup(=cfs_rq) to another. i tested with "echo pid > cgroup" and
found that e.g. cfs_rq->avg.load_avg became larger and larger whenever i
changed a cgroup to another again and again.

we have to sync se's average load with both *prev* cfs_rq and next cfs_rq
when changing its group.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
 kernel/sched/fair.c |   24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2a33d7b..25028b9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8017,8 +8017,28 @@ static void task_move_group_fair(struct task_struct *p, int queued)
 	if (!queued && (!se->sum_exec_runtime || p->state == TASK_WAKING))
 		queued = 1;
 
-	if (!queued)
-		se->vruntime -= cfs_rq_of(se)->min_vruntime;
+	if (!queued) {
+		cfs_rq = cfs_rq_of(se);
+		se->vruntime -= cfs_rq->min_vruntime;
+
+#ifdef CONFIG_SMP
+		/*
+		 * synchronize task with its prev cfs_rq
+		 * remove our load when we leave
+		 */
+		__update_load_avg(cfs_rq->avg.last_update_time, cpu_of(rq_of(cfs_rq)), &se->avg,
+				se->on_rq * scale_load_down(se->load.weight), cfs_rq->curr == se, NULL);
+
+		cfs_rq->avg.load_avg =
+			max_t(long, cfs_rq->avg.load_avg - se->avg.load_avg, 0);
+		cfs_rq->avg.load_sum =
+			max_t(s64, cfs_rq->avg.load_sum - se->avg.load_sum, 0);
+		cfs_rq->avg.util_avg =
+			max_t(long, cfs_rq->avg.util_avg - se->avg.util_avg, 0);
+		cfs_rq->avg.util_sum =
+			max_t(s32, cfs_rq->avg.util_sum - se->avg.util_sum, 0);
+#endif
+	}
 	set_task_rq(p, task_cpu(p));
 	se->depth = se->parent ? se->parent->depth + 1 : 0;
 	if (!queued) {
-- 
1.7.9.5

Re: [PATCH v3] sched: sync with the prev cfs when changing cgroup within a cpu

[Yuyang Du]

On Wed, Aug 12, 2015 at 04:05:15PM +0900, byungchul.park@lge.com wrote:
> 
> current code seems to be wrong with cfs_rq's avg loads when changing
> a task's cgroup(=cfs_rq) to another. i tested with "echo pid > cgroup" and
> found that e.g. cfs_rq->avg.load_avg became larger and larger whenever i
> changed a cgroup to another again and again.
> 
> we have to sync se's average load with both *prev* cfs_rq and next cfs_rq
> when changing its group.
> 

I think you are right in general, it has nothing to do with
migrate_task_rq_fair() and the load should be carried to new cfs_rq.

But whether it is queued or not should be doing the same thing, so what about:

/* if queued, the previous dequeue_task() should have already done it */
if (!queued)
	__upload_load_avg()

remove_from_old_cfs_rq();

/* virtually catch up because of the skew between cfs_rqs */
task's last_update_time = cfs_rq's last_update_time;
add_to_new_cfs_rq();

Thanks,
Yuyang

Re: [PATCH v3] sched: sync with the prev cfs when changing cgroup within a cpu

[Byungchul Park]

On Wed, Aug 12, 2015 at 09:05:48AM +0800, Yuyang Du wrote:
> On Wed, Aug 12, 2015 at 04:05:15PM +0900, byungchul.park@lge.com wrote:
> > 
> > current code seems to be wrong with cfs_rq's avg loads when changing
> > a task's cgroup(=cfs_rq) to another. i tested with "echo pid > cgroup" and
> > found that e.g. cfs_rq->avg.load_avg became larger and larger whenever i
> > changed a cgroup to another again and again.
> > 
> > we have to sync se's average load with both *prev* cfs_rq and next cfs_rq
> > when changing its group.
> > 
> 
> I think you are right in general, it has nothing to do with
> migrate_task_rq_fair() and the load should be carried to new cfs_rq.
> 
> But whether it is queued or not should be doing the same thing, so what about:

hello yuyang,

i worked with code based on torvalds git, but now.. in tip git where sched
code is renewed much, i think you are right. i will fix it.

thank you much. :)
Byungchul

> 
> /* if queued, the previous dequeue_task() should have already done it */
> if (!queued)
> 	__upload_load_avg()
> 
> remove_from_old_cfs_rq();
> 
> /* virtually catch up because of the skew between cfs_rqs */
> task's last_update_time = cfs_rq's last_update_time;
> add_to_new_cfs_rq();
> 
> Thanks,
> Yuyang
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