[openstack-dev] [nova][scheduler][placement] Allocating Complex Resources

Jay Pipes jaypipes at gmail.com
Mon Jun 12 18:29:48 UTC 2017

On 06/12/2017 02:17 PM, Edward Leafe wrote:
> On Jun 12, 2017, at 10:20 AM, Jay Pipes <jaypipes at gmail.com 
> <mailto:jaypipes at gmail.com>> wrote:
>>> The RP uuid is part of the provider: the compute node's uuid, and 
>>> (after https://review.openstack.org/#/c/469147/ merges) the PCI 
>>> device's uuid. So in the code that passes the PCI device information 
>>> to the scheduler, we could add that new uuid field, and then the 
>>> scheduler would have the information to a) select the best fit and 
>>> then b) claim it with the specific uuid. Same for all the other 
>>> nested/shared devices.
>> How would the scheduler know that a particular SRIOV PF resource 
>> provider UUID is on a particular compute node unless the placement API 
>> returns information indicating that SRIOV PF is a child of a 
>> particular compute node resource provider?
> Because PCI devices are per compute node. The HostState object populates 
> itself from the compute node here:
> https://github.com/openstack/nova/blob/master/nova/scheduler/host_manager.py#L224-L225
> If we add the UUID information to the PCI device, as the above-mentioned 
> patch proposes, when the scheduler selects a particular compute node 
> that has the device, it uses the PCI device’s UUID. I thought that 
> having that information in the scheduler was what that patch was all about.

I would hope that over time, there's be little to no need for the 
scheduler to read either the compute_nodes or the pci_devices tables 
(which, btw, are in the cell databases). The information that the 
scheduler currently keeps in the host state objects should eventually be 
able to be primarily constructed by the returned results from the 
placement API instead of the existing situation where the scheduler must 
make multiple calls to the multiple cells databases in order to fill 
that information in.


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