When NUMA and CPU balancing were reconciled, there was an attempt to allow a degree of imbalance but it caused more problems than it solved. Instead, imbalance was only allowed with an almost idle NUMA domain. A lot of the problems have since been addressed so it's time for a revisit. There is also an issue with how fork is balanced across threads. It's mentioned in this context as patch 2 and 3 should share similar behaviour in terms of a nodes utilisation.
Patch 1 is just a cosmetic rename Patch 2 allows a "floating" imbalance to exist so communicating tasks can remain on the same domain until utilisation is higher. It aims to balance compute availability with memory bandwidth. Patch 3 is the interesting one. Currently fork can allow a NUMA node to be completely utilised as long as there are idle CPUs until the load balancer gets involved. This caused serious problems with a real workload that unfortunately I cannot share many details about but there is a proxy reproducer. kernel/sched/fair.c | 41 ++++++++++++++++++++++++----------------- 1 file changed, 24 insertions(+), 17 deletions(-)