Re: [PATCH v5 1/2] qom: new object to associate device to numa node

[Markus Armbruster]

<ankita@nvidia.com> writes:

> From: Ankit Agrawal <ankita@nvidia.com>
>
> NVIDIA GPU's support MIG (Mult-Instance GPUs) feature [1], which allows
> partitioning of the GPU device resources (including device memory) into
> several (upto 8) isolated instances. Each of the partitioned memory needs
> a dedicated NUMA node to operate. The partitions are not fixed and they
> can be created/deleted at runtime.
>
> Unfortunately Linux OS does not provide a means to dynamically create/destroy
> NUMA nodes and such feature implementation is not expected to be trivial. The
> nodes that OS discovers at the boot time while parsing SRAT remains fixed. So
> we utilize the Generic Initiator Affinity structures that allows association
> between nodes and devices. Multiple GI structures per BDF is possible,
> allowing creation of multiple nodes by exposing unique PXM in each of these
> structures.
>
> Introduce a new acpi-generic-initiator object to allow host admin provide the
> device and the corresponding NUMA nodes. Qemu maintain this association and
> use this object to build the requisite GI Affinity Structure.

Pardon my ignorance...  What makes this object an "initiator", and why
is it "generic"?

> An admin can provide the range of nodes through a uint16 array host-nodes
> and link it to a device by providing its id. Currently, only PCI device is
> supported. The following sample creates 8 nodes and link them to the PCI
> device dev0:
>
> -numa node,nodeid=2 \
> -numa node,nodeid=3 \
> -numa node,nodeid=4 \
> -numa node,nodeid=5 \
> -numa node,nodeid=6 \
> -numa node,nodeid=7 \
> -numa node,nodeid=8 \
> -numa node,nodeid=9 \
> -device 
> vfio-pci-nohotplug,host=0009:01:00.0,bus=pcie.0,addr=04.0,rombar=0,id=dev0 \
> -object acpi-generic-initiator,id=gi0,pci-dev=dev0,host-nodes=2-9 \

Does this link *all* NUMA nodes to dev0?

Would an example involving two devices be more instructive?

> [1] https://www.nvidia.com/en-in/technologies/multi-instance-gpu
>
> Signed-off-by: Ankit Agrawal <ankita@nvidia.com>

[...]

> diff --git a/qapi/qom.json b/qapi/qom.json
> index c53ef978ff..efcc4b8dfd 100644
> --- a/qapi/qom.json
> +++ b/qapi/qom.json
> @@ -794,6 +794,21 @@
>  { 'struct': 'VfioUserServerProperties',
>    'data': { 'socket': 'SocketAddress', 'device': 'str' } }
>  
> +##
> +# @AcpiGenericInitiatorProperties:
> +#
> +# Properties for acpi-generic-initiator objects.
> +#
> +# @pci-dev: PCI device ID to be associated with the node
> +#
> +# @host-nodes: numa node list

This feels a bit terse.  The commit message makes me guess this
specifies the NUMA nodes to be linked to @pci-dev.  Correct?

> +#
> +# Since: 9.0
> +##
> +{ 'struct': 'AcpiGenericInitiatorProperties',
> +  'data': { 'pci-dev': 'str',
> +            'host-nodes': ['uint16'] } }
> +
>  ##
>  # @RngProperties:
>  #
> @@ -911,6 +926,7 @@
>  ##
>  { 'enum': 'ObjectType',
>    'data': [
> +    'acpi-generic-initiator',
>      'authz-list',
>      'authz-listfile',
>      'authz-pam',
> @@ -981,6 +997,7 @@
>              'id': 'str' },
>    'discriminator': 'qom-type',
>    'data': {
> +      'acpi-generic-initiator':     'AcpiGenericInitiatorProperties',
>        'authz-list':                 'AuthZListProperties',
>        'authz-listfile':             'AuthZListFileProperties',
>        'authz-pam':                  'AuthZPAMProperties',