Since providers can be nested a provider can be a strucutral element in a nested tree without providing resources.
This. I wouldn't get too hung up on "a resource provider that doesn't provide resources". "Resource provider" is just a name of a thing. It doesn't (can't) exhaustively define what the thing is and does.
To avoid the trait on an empty RP problem in this case all the traits are added to the device RPs even if some of the traits (CUSTOM_VNIC_TYPE_XXX) are more logically belong to the agnet RP.
Noting that I have at best a cursory understanding of all things network, this seems okay to me; I can get my brain around a "network device" having a "VNIC type" trait. However...
I think the possible solution to move the trait down to the RP that provides the resources that has a capability described by the trait
In Matt's patch, the traits represent capabilities of the virt driver. I *suppose* you could argue to attach traits like COMPUTE_NET_ATTACH_INTERFACE to providers of network resources, or COMPUTE_VOLUME_EXTEND to providers of disk resources (even those are pretty awkward). But where would you put COMPUTE_TRUSTED_CERTS? And let's please not contrive non-resource resources to satisfy architectural purity.
I think this work should be driven by a specific need, like the NUMA modelling in placement by nova. What is the timeline of NUMA modelling in placement?
Proposes NUMA topology with RPs: https://review.openstack.org/552924 Proposes NUMA affinity for vGPUs: https://review.openstack.org/650963 Spec: Allocation Candidates: Subtree Affinity: https://review.openstack.org/650476 and a bunch of the other specs in flight are affected by NUMA modeling. We've been building up to this for years. If it doesn't happen in Train, it'll happen in U. While I agree we shouldn't solve a problem until it's a problem, I also don't want to another situation like reshaper, where suddenly at the end of the cycle we realize/remember this nontrivial thing we need to handle. efried .