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Date: Thu, 27 Feb 2014 16:49:49 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [snabb-devel] Re: Make virtio-net.c ring size
 configurable?
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Luke Gorrie <luke@snabb.co>, "snabb-devel@googlegroups.com" <snabb-devel@googlegroups.com>, qemu-devel <qemu-devel@nongnu.org>

On Thu, Feb 27, 2014 at 03:17:44PM +0100, Stefan Hajnoczi wrote:
> On Mon, Feb 24, 2014 at 05:14:04PM +0100, Luke Gorrie wrote:
> > On 24 February 2014 16:20, Stefan Hajnoczi <stefanha@gmail.com> wrote:
> > 
> > > Do you want the 1:1 mapping to achieve best performance or just to
> > > simplify the coding?
> > >
> > 
> > We want to keep the real-time constraints on the data plane comfortable.
> > 
> > The question I ask myself is: How long can I buffer packets during
> > processing before something is dropped?
> > 
> > 256 buffers can be consumed in 17 microseconds on a 10G interface.
> 
> This is a good point.  The virtio-net vring is too small at 256 buffers
> for workloads that want to send/receive small packets at 10 Gbit/s line
> rate.  (Minimum UDP packet size is 52 bytes!)
> 
> Michael: Luke has asked to increase the virtio-net virtqueue size.
> Thoughts?
> 
> Stefan

Heh you want to increase the bufferbloat?
Each buffer pointer takes up 16 bytes so we are using order-2
allocations as it is, anything more and it'll start to fail
if hotplug happens long after boot.

AFAIK baremetal does not push line rate with 1 byte payload
either.

-- 
MST