[dpdk-dev] rte_eth_dev_socket_id() vs KVM/AWS/...

[Mike Stolarchuk <mike.stolarchuk@bigswitch.com>]

Hello Dpdk,

rte_eth_dev_socket_id() describes a -1 return value as:

*Returns*

The NUMA socket id to which the Ethernet device is connected or a default
of zero if the socket could not be determined. -1 is returned is the
port_id value is out of range.

But, rte_eth_dev_socket_id() is implemented as:

int
rte_eth_dev_socket_id(uint16_t port_id)
{
    RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, -1);
    return rte_eth_devices[port_id].data->numa_node;
}

And numa_node here is set from /sys/bus/pci/<device>/numa_node.
And https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-bus-pci
documents numa_node as:

What: /sys/bus/pci/devices/.../numa_node
Date: Oct 2014
Contact: Prarit Bhargava <prarit@redhat.com>
Description:
This file contains the NUMA node to which the PCI device is
attached, or -1 if the node is unknown.  The initial value
comes from an ACPI _PXM method or a similar firmware
source.  If that is missing or incorrect, this file can be
written to override the node.  In that case, please report
a firmware bug to the system vendor.  Writing to this file
taints the kernel with TAINT_FIRMWARE_WORKAROUND, which
reduces the supportability of your system.

in other words, a value of -1 for numa_node means the association of the
pci device WRT socket is unknown.
And as an example, in a KVM with e1000's.
/sys/bus/pci/devices/<d>/numa_node can return -1.

This means that rte_eth_dev_socket_id() returns -1 in situations other than
'port_id value is out of range'.
And its not possible to identify whether the port_id is invalid, or whether
the base system didn't
announce the numa_node association.

Perhaps a -1 return value should be an indication the the numa_node
association isn't known,
and a different return value, say -2, should indicate the port_id value is
out of range.


mts.