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authorOdin Ugedal <[email protected]>2021-06-24 13:18:15 +0200
committerPeter Zijlstra <[email protected]>2021-06-28 15:42:24 +0200
commit1c35b07e6d3986474e5635be566e7bc79d97c64d (patch)
tree95af2f2d1be9845eb884cb67312b5a64fc80b80a
parentadf3c31e18b765ea24eba7b0c1efc076b8ee3d55 (diff)
sched/fair: Ensure _sum and _avg values stay consistent
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 <[email protected]> Reported-by: Naresh Kamboju <[email protected]> Signed-off-by: Odin Ugedal <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Reviewed-by: Vincent Guittot <[email protected]> Tested-by: Sachin Sant <[email protected]> Link: https://lore.kernel.org/r/[email protected]
-rw-r--r--kernel/sched/fair.c6
1 files changed, 3 insertions, 3 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4a3e61a88acc..45edf61eed73 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3657,15 +3657,15 @@ 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