Srikar had an automatic NUMA balancing series merged during the 4.19 window and there some issues I missed during review that this series addresses.
Patches 1-2 are simply removing redundant code and calculations that are never used. Patch 3 makes the observation that we can call select_idle_sibling during NUMA placement several times for each idle CPU on a socket. The patch stops the search on the first idle CPU. While there is the risk that parallel callers will stack on the same idle CPU, the current code has the same problem. Patch 4 is the one that needs the most examination. I believe intent of load_too_imbalanced was to stop automatic NUMA balancing fighting the load balancer. Unfortunately, when a machine is lightly utilised there are idle CPUs and tasks are allowed to migrate even though the load is imbalanced. In some cases, this limits memory bandwidth and can perform worse even if data locality is fine. The patch corrects the condition. If they pass review, I think it would suggest considering them a fix for 4.19 instead of deferring to 4.20. kernel/sched/fair.c | 35 ++++++++--------------------------- 1 file changed, 8 insertions(+), 27 deletions(-) -- 2.16.4