On 24 February 2014 16:20, Stefan Hajnoczi <stefa...@gmail.com> wrote:

> On Fri, Feb 14, 2014 at 02:43:14PM +0100, Luke Gorrie wrote:
> > In Snabb Switch we are creating a 1:1 mapping between Virtio-net
> > descriptors and VMDq hardware receive descriptors. The VMDq queues
> support
> > 32768 buffers and I'd like to match this on the QEMU/Virtio-net side --
> or
> > at least come close.
>

[...]


> Do you want the 1:1 mapping to achieve best performance or just to
> simplify the coding?
>

More background:

The 1:1 mapping between hardware RX descriptors and Virtio-net descriptors
is for best performance, specifically for zero-copy operation. We want the
NIC to DMA the packets directly into guest memory and that's why we need to
pre-populate the NIC descriptor lists with suitable memory obtained from
the guest via the Virtio-net avail ring.

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