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

Sylvain Bauza sbauza at redhat.com
Wed Jun 3 08:09:57 UTC 2015

Le 03/06/2015 04:17, Chris Friesen a écrit :
> On 06/02/2015 07:48 PM, Jay Pipes wrote:
>> On 06/02/2015 07:25 PM, Chris Friesen wrote:
>>> 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.
> If the nova-compute node is still the final arbiter, what does it 
> actually mean to say that the scheduler "owns" the records?

That's not ambivalent. Considering that the placement decision is made 
by the Scheduler(s) ( note the -s- ), it means that the scheduler is the 
thing who owns the resource usage.

Of course, it also means that the compute node is only here as a 
last-standing-man to make sure it can handle the request. But if it 
can't, it has to report to the scheduler that the placement decision was 
incorrect, so the scheduler can make adjustements if necessary.


> Chris
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