From: Odin Ugedal odin@uged.al
[ 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@linux.vnet.ibm.com Reported-by: Naresh Kamboju naresh.kamboju@linaro.org Signed-off-by: Odin Ugedal odin@uged.al Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Vincent Guittot vincent.guittot@linaro.org Tested-by: Sachin Sant sachinp@linux.vnet.ibm.com Link: https://lore.kernel.org/r/20210624111815.57937-1-odin@uged.al Signed-off-by: Sasha Levin sashal@kernel.org --- 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 d6e1c90de570..78f4ebc6ac98 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