This is a note to let you know that I've just added the patch titled
sched/fair: Ensure _sum and _avg values stay consistent
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-fair-ensure-_sum-and-_avg-values-stay-consiste.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 1d1ea92e3af733f0c41e47594d507a815a871a71
Author: Odin Ugedal <odin@xxxxxxx>
Date: Thu Jun 24 13:18:15 2021 +0200
sched/fair: Ensure _sum and _avg values stay consistent
[ Upstream commit 1c35b07e6d3986474e5635be566e7bc79d97c64d ]
The _sum and _avg values are in general sync together with the PELT
divider. They are however not always completely in perfect sync,
resulting in situations where _sum gets to zero while _avg stays
positive. Such situations are undesirable.
This comes from the fact that PELT will increase period_contrib, also
increasing the PELT divider, without updating _sum and _avg values to
stay in perfect sync where (_sum == _avg * divider). However, such PELT
change will never lower _sum, making it impossible to end up in a
situation where _sum is zero and _avg is not.
Therefore, we need to ensure that when subtracting load outside PELT,
that when _sum is zero, _avg is also set to zero. This occurs when
(_sum < _avg * divider), and the subtracted (_avg * divider) is bigger
or equal to the current _sum, while the subtracted _avg is smaller than
the current _avg.
Reported-by: Sachin Sant <sachinp@xxxxxxxxxxxxxxxxxx>
Reported-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
Signed-off-by: Odin Ugedal <odin@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Tested-by: Sachin Sant <sachinp@xxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210624111815.57937-1-odin@xxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3d92de7909bf..32c0905bca84 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3672,15 +3672,15 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
r = removed_load;
sub_positive(&sa->load_avg, r);
- sub_positive(&sa->load_sum, r * divider);
+ sa->load_sum = sa->load_avg * divider;
r = removed_util;
sub_positive(&sa->util_avg, r);
- sub_positive(&sa->util_sum, r * divider);
+ sa->util_sum = sa->util_avg * divider;
r = removed_runnable;
sub_positive(&sa->runnable_avg, r);
- sub_positive(&sa->runnable_sum, r * divider);
+ sa->runnable_sum = sa->runnable_avg * divider;
/*
* removed_runnable is the unweighted version of removed_load so we
