[openstack-dev] [nova] I think nova behaves poorly when booting multiple instances

Jay Pipes jaypipes at gmail.com
Wed Jun 3 01:48:16 UTC 2015

On 06/02/2015 07:25 PM, Chris Friesen wrote:
> On 06/02/2015 02:36 PM, Andrew Laski wrote:
>> There used to be a project that I think was looking for an API like
>> this to
>> provide a reservation system, Climate or Blazar or something.  There
>> was brief
>> talk of providing something like it for that use case, but the idea
>> was put on
>> the backburner to wait for the scheduling rework that's occurring.
>> The question in my mind is should the claim requests be in the Nova
>> API or come
>> from a scheduler API.  And I tend to think that they should come from a
>> scheduler API.
> Who owns the resources, nova or the scheduler?
> In many cases only nova-compute can resolve races (resource tracking of
> specific CPU cores, specific PCI devices, etc. in the face of parallel
> scheduling) so unless we're going to guarantee no races then I think
> claim requests should be a nova API call, and it should go all the way
> down to nova-compute to make sure that the resources are actually claimed.

That's actually how the system works today. And, IMHO, it's inefficient. 
The nova-compute node should be the final arbiter of whether a request 
for resources can be properly fulfilled by the hypervisor, however, the 
scheduler should be the thing that "owns" resource usage records for the 
partition of resource providers that the scheduler process is 
responsible for.

I think the claim IDs should be returned from the scheduler API instead 
of created within the nova-compute manager.


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