Query regarding netvsc PMD : VF removal

[Nandini Rangaswamy]

Hi Stephen and Long,
I am trying to understand the complete packet path and I am confused here.
The synthetic device is being created and managed by a driver in guest
kernel space.
Shouldn't the packets be directly DMAed from NIC to VFs in guest. If all
packets go through synthetic interface to the VF, then wouldn't kernel get
involved here and defeat the purpose of DPDK ?
Please find attached a block diagram that i came up with highlights the
devices and drivers and my understanding of their interactions.
I have shown in the diagram that for every VNIC , a synthetic and VF is
present . Synthetic interfaces are managed by uio_hv_generic and VFs that
appear as PCI devices in the guest kernel are managed by MLNX.
I have also shown that netvsc pmd depends on uio_hv_generic module. The red
arrow represents synthetic data path and green arrows represent the
accelerated data path.
I am still unclear about pkt flow from NIC to VF through synthetic
interface and vice-versa involving netvsc pmd, mlnx driver/PMD.
Can you please clarify this?
Regards,
Nandini


On Thu, Jul 25, 2024 at 2:52 PM Stephen Hemminger <
stephen at networkplumber.org> wrote:

> On Thu, 25 Jul 2024 11:41:59 -0700
> Nandini Rangaswamy <nandini.rangaswamy at broadcom.com> wrote:
>
> > Hi Stephen,
> > I am using the DPDK 22.11.5 LTS. Should the DPDK code take care of
> > unbinding synthetic interface from uio_hv_generic or should it be done by
> > the app when it gets hotplug notification?
> > Regards,
> > Nandini
>
> The synthetic device (netvsc) controlled by uio_hv_generic is never hot
> plugged.
> Only the VF which is mlx device can be removed and added.
> The management of the VF for traffic is handled completely internally to
> the netvsc device (same as the Linux netdevice). What happens is the
> host notifys the guest over vmbus when VF changes. For devices handled
> by the DPDK (netvsc PMD), this notification causes it to add/remove use
> of the VF.
>
> The VF should not be used directly. The synthetic device (netvsc) routes
> traffic over the VF and reads from it when it is present and up.
>

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