Nick Piggin wrote:
Hello Nick & all,Right. It may make more sense to have the setup based on some maximum distance between nodes. Eg. all nodes less than distance 10 away from node0 are to be in node0's first level NUMA domain (the next level is always global, IIRC).
Then you would still need some configuration option, but it would appear to be a more useful metric to use.
Do you mean that there should ever be only one NUMA sched-domain level ?
On a 2x4x4 cpus machine, we could in theory have SD_NODES_PER_DOMAIN=4, thus providing a 2 level NUMA sched-domain (domain 0 spans 4 cpus, domain 1 spans 16, domain 2 is global and spans 32).
But it is true that this configuration does not show evident performance gains upon SD_NODES_PER_DOMAIN=8 (domain 0 spans 4 cpus, domain 1 is global and spans 32), at least on parallel compilation of the kernel.
Providing SD_NODES_PER_DOMAIN as a boot parameter was also intended to choose between a multilevel sched-domains or not.
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Sinc�res salutations.
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