Re: [dpdk-dev] A Question about the necessity of DPDK VF for Ethernet PMDs

[Alejandro Lucero <alejandro.lucero@netronome.com>]

On Mon, Feb 4, 2019 at 12:19 PM Rami Rosen <ramirose@gmail.com> wrote:

> Hi, Alejandro,
>
> Thanks for you quick response.
>
> >When SRIOV is used by VMs, the slow path will always be faster (and
> >with lower latency) with DPDK.
>
> Yes, I am referring primarily to the SRIOV case in my question, when
> assigning PCI VF to a VM (most likely QEMU VM)
> Can you please explain what you mean about slow path in this context ?
>
>
First packets from a new VM connection will go through the slow path. With
SRIOV and assuming OVS offload, that implies the NIC sending the first
packet up to OVS through the PF and back down once OVS decides what to do
with that flow (including likely some flow rule offload).


> Not sure the OVS setup is relevant here, it seems (if I understand
> correctly) that VFIO is more commonly used in OVS setups,
> so this query is not relevant here (unless you use igb_uio which is less
> common)
>

I do not understand what you mean. VFIO is preferred because it is the
right way of doing IOMMU, and also the only way if OVS run as non-root.
If you have VMs using SRIOV, you need something like OVS in the host, and
here it comes the potential benefit of OVS DPDK, because any OVS required
action will likely be faster.


> According to
> http://docs.openvswitch.org/en/latest/intro/install/dpdk/
> "VFIO is prefered to the UIO driver when using recent versions of DPDK. "
> Regards,
> Rami Rosen
>
>
>
>