Changelog since v2
o Build fix for !NUMA_BALANCING configurations
Changelog since v1
o Split out patch that moves imbalance calculation
o Strongly connect fork imbalance considerations with adjust_numa_imbalance
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 3 and 4 should share similar behaviour in terms
of a nodes utilisation.
Patch 1 is just a cosmetic rename
Patch 2 moves an imbalance calculation. It is both a micro-optimisation
and avoids confusing what imbalance means for different group
types.
Patch 3 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 4 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.
--
2.26.2
Mel Gorman (4):
sched/numa: Rename nr_running and break out the magic number
sched: Avoid unnecessary calculation of load imbalance at clone time
sched/numa: Allow a floating imbalance between NUMA nodes
sched: Limit the amount of NUMA imbalance that can exist at fork time
kernel/sched/fair.c | 44 +++++++++++++++++++++++++++++++-------------
1 file changed, 31 insertions(+), 13 deletions(-)
--
2.26.2
