Re: [Qemu-devel] [snabb-devel] Re: Make virtio-net.c ring size configurable?

[Luke Gorrie]

On 24 February 2014 16:20, Stefan Hajnoczi <address@hidden> 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.