ComputeDriver.update_provider_tree¶

Background¶

In the movement towards using placement for scheduling and resource management, the virt driver method get_available_resource was initially superseded by get_inventory, whereby the driver could specify its inventory in terms understood by placement. In Queens, a get_traits driver method was added. But get_inventory is limited to expressing only inventory (not traits or aggregates). And both of these methods are limited to the resource provider corresponding to the compute node.

Recent developments such as Nested Resource Providers necessitate the ability for the virt driver to have deeper control over what the resource tracker configures in placement on behalf of the compute node. This need is filled by the virt driver method update_provider_tree and its consumption by the resource tracker, allowing full control over the placement representation of the compute node and its associated providers.

The Method¶

update_provider_tree accepts two parameters:

• A nova.compute.provider_tree.ProviderTree object representing all the providers in the tree associated with the compute node, and any sharing providers (those with the MISC_SHARES_VIA_AGGREGATE trait) associated via aggregate with any of those providers (but not their tree- or aggregate-associated providers), as currently known by placement. This object is fully owned by the update_provider_tree method, and can therefore be modified without locking/concurrency considerations. In other words, the parameter is passed by reference with the expectation that the virt driver will modify the object. Note, however, that it may contain providers not directly owned/controlled by the compute host. Care must be taken not to remove or modify such providers inadvertently. In addition, providers may be associated with traits and/or aggregates maintained by outside agents. The update_provider_tree method must therefore also be careful only to add/remove traits/aggregates it explicitly controls.
• String name of the compute node (i.e. ComputeNode.hypervisor_hostname) for which the caller is requesting updated provider information. Drivers may use this to help identify the compute node provider in the ProviderTree. Drivers managing more than one node (e.g. ironic) may also use it as a cue to indicate which node is being processed by the caller.

The virt driver is expected to update the ProviderTree object with current resource provider and inventory information. When the method returns, the ProviderTree should represent the correct hierarchy of nested resource providers associated with this compute node, as well as the inventory, aggregates, and traits associated with those resource providers.

         CN1                 SHR_ROOT               CN2
        /   \       agg1    /   /\     agg1        /   \
   NUMA1     NUMA2--------SSP--/--\-----------NUMA1     NUMA2
  /     \   /    \            /    \         /     \   /    \
PF1    PF2 PF3   PF4--------BW1   BW2------PF1    PF2 PF3   PF4
                     agg2             agg3

         CN1 (root)
        /   \       agg1
   NUMA1     NUMA2-------SSP (root)
  /     \   /    \
PF1    PF2 PF3   PF4------BW1 (root)
                     agg2

This method supersedes get_inventory and get_traits: if this method is implemented, neither get_inventory nor get_traits is used.

Driver implementations of update_provider_tree are expected to use public ProviderTree methods to effect changes to the provider tree passed in. Some of the methods which may be useful are as follows:

• new_root: Add a new root provider to the tree.
• new_child: Add a new child under an existing provider.
• data: Access information (name, UUID, parent, inventory, traits, aggregates) about a provider in the tree.
• remove: Remove a provider and its descendants from the tree. Use caution in multiple-ownership scenarios.
• update_inventory: Set the inventory for a provider.
• add_traits, remove_traits: Set/unset virt-owned traits for a provider.
• add_aggregates, remove_aggregates: Set/unset virt-owned aggregate associations for a provider.

def get_inventory(self, nodename):
    inv_data = {
        'VCPU': { ... },
        'MEMORY_MB': { ... },
        'DISK_GB': { ... },
    }
    return inv_data

def update_provider_tree(self, provider_tree, nodename):
    inv_data = {
        'VCPU': { ... },
        'MEMORY_MB': { ... },
        'DISK_GB': { ... },
    }
    provider_tree.update_inventory(nodename, inv_data)

def get_traits(self, nodename):
    traits = ['HW_CPU_X86_AVX', 'HW_CPU_X86_AVX2', 'CUSTOM_GOLD']
    return traits

def update_provider_tree(self, provider_tree, nodename):
    provider_tree.add_traits(
        nodename, 'HW_CPU_X86_AVX', 'HW_CPU_X86_AVX2', 'CUSTOM_GOLD')