Re: [Qemu-devel] [PATCH v1 0/6] Extend vhost-user to support VFIO based accelerators

[Stefan Hajnoczi]

On Thu, Jan 25, 2018 at 12:03:22PM +0800, Tiwei Bie wrote:
> Why extend vhost-user for vDPA
> ==============================
> 
> We have already implemented various virtual switches (e.g. OVS-DPDK)
> based on vhost-user for VMs in the Cloud. They are purely software
> running on CPU cores. When we have accelerators for such NFVi applications,
> it's ideal if the applications could keep using the original interface
> (i.e. vhost-user netdev) with QEMU, and infrastructure is able to decide
> when and how to switch between CPU and accelerators within the interface.
> And the switching (i.e. switch between CPU and accelerators) can be done
> flexibly and quickly inside the applications.
> 
> More details about this can be found from the Cunming's discussions on
> the RFC patch set.
> 
> The previous links:
> RFC: http://lists.nongnu.org/archive/html/qemu-devel/2017-12/msg04844.html

Is vDPA also useful in the simpler use case where there is no NFVi
application?

In other words, you have virtio-net inside the guest and vhost-net on
the host.  You'd like to accelerate the virtio-net NIC using the
hardware's vDPA support.

DPDK requires dedicated logical cores and hugepages.  Those resources
will not be used (wasted) if you just want to enable vDPA but have no
DPDK packet processing application.

How can this use case be supported without wasting resources?

Stefan

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