[openstack-dev] [neutron] [nova] scheduling bandwidth resources / NIC_BW_KB resource class

Sylvain Bauza sbauza at redhat.com
Fri Apr 22 07:48:45 UTC 2016

Le 22/04/2016 02:49, Jay Pipes a écrit :
> On 04/20/2016 06:40 PM, Matt Riedemann wrote:
>> Note that I think the only time Nova gets details about ports in the API
>> during a server create request is when doing the network request
>> validation, and that's only if there is a fixed IP address or specific
>> port(s) in the request, otherwise Nova just gets the networks. [1]
>> [1]
>> https://github.com/openstack/nova/blob/ee7a01982611cdf8012a308fa49722146c51497f/nova/network/neutronv2/api.py#L1123 
> Actually, nova.network.neutronv3.api.API.allocate_for_instance() is 
> *never* called by the Compute API service (though, strangely, 
> deallocate_for_instance() *is* called by the Compute API service.
> allocate_for_instance() is *only* ever called in the nova-compute 
> service:
> https://github.com/openstack/nova/blob/7be945b53944a44b26e49892e8a685815bf0cacb/nova/compute/manager.py#L1388 
> I was actually on a hangout today with Carl, Miguel and Dan Smith 
> talking about just this particular section of code with regards to 
> routed networks IPAM handling.
> What I believe we'd like to do is move to a model where we call out to 
> Neutron here in the conductor:
> https://github.com/openstack/nova/blob/7be945b53944a44b26e49892e8a685815bf0cacb/nova/conductor/manager.py#L397 
> and ask Neutron to give us as much information about available subnet 
> allocation pools and segment IDs as it can *before* we end up calling 
> the scheduler here:
> https://github.com/openstack/nova/blob/7be945b53944a44b26e49892e8a685815bf0cacb/nova/conductor/manager.py#L415 
> Not only will the segment IDs allow us to more properly use network 
> affinity in placement decisions, but doing this kind of "probing" for 
> network information in the conductor is inherently more scalable than 
> doing this all in allocate_for_instance() on the compute node while 
> holding the giant COMPUTE_NODE_SEMAPHORE lock.

I totally agree with that plan. I never replied to Ajo's point (thanks 
Matt for doing that) but I was struggling to figure out an allocation 
call in the Compute API service. Thanks Jay for clarifying this.

Funny, we do *deallocate* if an exception is raised when trying to find 
a destination in the conductor, but since the port is not allocated yet, 
I guess it's a no-op at the moment.


Clarifying the above and making the conductor responsible for placing 
calls to Neutron is something I'd love to see before moving further with 
the routed networks and the QoS specs, and yes doing that in the 
conductor seems to me the best fit.


> Best,
> -jay
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