[nova] Do we need to copy pci_devices to target cell DB during cross-cell resize?

Matt Riedemann mriedemos at gmail.com
Tue Jan 22 22:47:36 UTC 2019

On 1/22/2019 12:19 PM, Sean Mooney wrote:
> you are specifically doing a resize so you dont need to regenerate a new xml
> on the source node before starting a live migration sice its not a live migration
> but you might want to premtpvily allcoate the pci devices on the destination
> if you want to prevent a race with other hosts. That said for stien it may be better
> to declare that out of scope. its really not any more racy then spawning an instace
> as we dont claim the device untill we get to the compute node anyway today.

Correct, and the plan for cross-cell resize is to do the same 
RT.resize_claim on the target host in the target cell before trying to 
move anything, which is the same thing we do in 
ComputeManager.prep_resize for a normal resize within the same cell.

> the instance.numa_topology shoudl really be recalulated for the target host also.
> you do not want to require the destination host to place the vm with the original
> numa toptolgy from the source node. so i think you need to propagate the numa related
> request which are all in the flavor/image but i dont think you need to copy
> the instance numa_topology object. its not a live migration so provided the

The instance.numa_topology is calculated from the flavor and image 
during the initial server create:


And during the MoveClaim:


So yeah it looks like I don't really have to worry about 
updating/setting instance.numa_topology in the target cell DB during the 
resize although it seems pretty weird that we leave that stale 
information in the instances table during a resize (it's also stale in 
the RequestSpec - I think Alex Xu reported a bug for that).




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