From: Odin Ugedal <odin@xxxxxxx> [ 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> --- kernel/sched/fair.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 47fcc3fe9dc5..b4fa8b16c69c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3665,15 +3665,15 @@ 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 -- 2.30.2
