Re: Regarding Mellanox bifurcated driver on Azure

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 25 Apr 2025 23:17:30 +0530
Prashant Upadhyaya <praupadhyaya@gmail.com> wrote:

> Hi,
> 
> I am having a VM on Azure where I have got two 'accelerated networking'
> interfaces of Mellanox
> # lspci -nn|grep -i ether
> 6561:00:02.0 Ethernet controller [0200]: Mellanox Technologies MT27710
> Family [ConnectX-4 Lx Virtual Function] [15b3:1016] (rev 80)
> f08c:00:02.0 Ethernet controller [0200]: Mellanox Technologies MT27710
> Family [ConnectX-4 Lx Virtual Function] [15b3:1016] (rev 80)
> 
> I have a DPDK application which needs to obtain 'all' packets from the NIC.
> I installed the drivers, compiled DPDK24.11 (Ubuntu20.04), my app starts
> and is able to detect the NIC's.
> Everything looks good
> myapp.out -c 0x07 -a f08c:00:02.0 -a 6561:00:02.0
> EAL: Detected CPU lcores: 8
> EAL: Detected NUMA nodes: 1
> EAL: Detected shared linkage of DPDK
> EAL: Multi-process socket /var/run/dpdk/rte/mp_socket
> EAL: Selected IOVA mode 'PA'
> EAL: VFIO support initialized
> mlx5_net: Default miss action is not supported.
> mlx5_net: Default miss action is not supported.
> All Ports initialized
> Port 0 is UP (50000 Mbps)
> Port 1 is UP (50000 Mbps)
> 
> The trouble is that the ARP packets are not being picked up by my DPDK
> application, I see them being delivered to the kernel via the eth interface
> corresponding to the port (MLX is a bifurcated driver, you don't really
> bind to the NIC, so you still see the eth interfaces at linux level and can
> run tcpdump on those, I see ARP packets in the tcpdump there on the
> interface)
> I can receive UDP packets in my DPDK app though.
> 
> My application is not setting any rte_flow rules etc. so I was expecting
> that by default my dpdk app would get all the packets as is normally the
> case with other NIC's
> Is there something I need to configure for Mellanox NIC somewhere such that
> I get 'all' the packets including ARP packets in my DPDK app ?
> 
> Regards
> -Prashant

The Mellanox device in Azure networking cards is only used as a VF switch.
You can go back to earlier DPDK presentations for more detail.

Three reason bifurcation won't work.
 1. Only some of the packets arrive on the VF. All non-IP show up on
    the synthetic device. The VF is only used after the TCP three way
    handshake.
 2. The Netvsc PMD doesn't handle flow rules.
 3. The VF can be removed and restored any time (by hypervisor)
    it is not a stable entity.