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

Matt Riedemann mriedem at linux.vnet.ibm.com
Wed Apr 20 22:40:18 UTC 2016

On 4/20/2016 8:25 AM, Miguel Angel Ajo Pelayo wrote:
> Inline update.
> On Mon, Apr 11, 2016 at 4:22 PM, Miguel Angel Ajo Pelayo
> <majopela at redhat.com> wrote:
>> On Mon, Apr 11, 2016 at 1:46 PM, Jay Pipes <jaypipes at gmail.com> wrote:
>>> On 04/08/2016 09:17 AM, Miguel Angel Ajo Pelayo wrote:
> [...]
>>> Yes, Nova's conductor gathers information about the requested networks
>>> *before* asking the scheduler where to place hosts:
>>> https://github.com/openstack/nova/blob/stable/mitaka/nova/conductor/manager.py#L362
>>>>      That would require identifying that the port has a "qos_policy_id"
>>>> attached to it, and then, asking neutron for the specific QoS policy
>>>>   [3], then look out for a minimum bandwidth rule (still to be defined),
>>>> and extract the required bandwidth from it.
>>> Yep, exactly correct.
>>>>     That moves, again some of the responsibility to examine and
>>>> understand external resources to nova.
>>> Yep, it does. The alternative is more retries for placement decisions
>>> because accurate decisions cannot be made until the compute node is already
>>> selected and the claim happens on the compute node.
>>>>      Could it make sense to make that part pluggable via stevedore?, so
>>>> we would provide something that takes the "resource id" (for a port in
>>>> this case) and returns the requirements translated to resource classes
>>>> (NIC_BW_KB in this case).
>>> Not sure Stevedore makes sense in this context. Really, we want *less*
>>> extensibility and *more* consistency. So, I would envision rather a system
>>> where Nova would call to Neutron before scheduling when it has received a
>>> port or network ID in the boot request and ask Neutron whether the port or
>>> network has any resource constraints on it. Neutron would return a
>>> standardized response containing each resource class and the amount
>>> requested in a dictionary (or better yet, an os_vif.objects.* object,
>>> serialized). Something like:
>>> {
>>>   'resources': {
>>>     '<UUID of port or network>': {
>>>       'NIC_BW_KB': 2048,
>>>       'IPV4_ADDRESS': 1
>>>     }
>>>   }
>>> }
>> Oh, true, that's a great idea, having some API that translates a
>> neutron resource, to scheduling constraints. The external call will be
>> still required, but the coupling issue is removed.
> I had a talk yesterday with @iharchys, @dansmith, and @sbauzas about
> this, and we believe the synthesis of resource usage / scheduling
> constraints from neutron makes sense.
> We should probably look into providing those details in a read only
> dictionary during port creation/update/show in general, in that way,
> we would not be adding an extra API call to neutron from the nova
> scheduler to figure out any of those details. That extra optimization
> is something we may need to discuss with the neutron community.

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]

>>> In the case of the NIC_BW_KB resource class, Nova's scheduler would look for
>>> compute nodes that had a NIC with that amount of bandwidth still available.
>>> In the case of the IPV4_ADDRESS resource class, Nova's scheduler would use
>>> the generic-resource-pools interface to find a resource pool of IPV4_ADDRESS
>>> resources (i.e. a Neutron routed network or subnet allocation pool) that has
>>> available IP space for the request.
>> Not sure about the IPV4_ADDRESS part because I still didn't look on
>> how they resolve routed networks with this new framework, but for
>> other constraints makes perfect sense to me.
>>> Best,
>>> -jay
>>>> Best regards,
>>>> Miguel Ángel Ajo
>>>> [1]
>>>> http://lists.openstack.org/pipermail/openstack-dev/2016-February/086371.html
>>>> [2] https://bugs.launchpad.net/neutron/+bug/1560963
>>>> [3]
>>>> http://developer.openstack.org/api-ref-networking-v2-ext.html#showPolicy
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Matt Riedemann

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