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Date: Thu, 24 Nov 2016 06:26:51 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 1/2] virtio-net rsc: support coalescing
 ipv4 tcp traffic
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To: Jason Wang <jasowang@redhat.com>
Cc: wexu@redhat.com, qemu-devel@nongnu.org, dfleytma@redhat.com, yvugenfi@redhat.com

On Thu, Nov 24, 2016 at 12:17:21PM +0800, Jason Wang wrote:
> > diff --git a/include/standard-headers/linux/virtio_net.h b/include/standard-headers/linux/virtio_net.h
> > index 30ff249..e67b36e 100644
> > --- a/include/standard-headers/linux/virtio_net.h
> > +++ b/include/standard-headers/linux/virtio_net.h
> > @@ -57,6 +57,9 @@
> >   					 * Steering */
> >   #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
> > +/* Guest can handle coalesced ipv4-tcp packets */
> > +#define VIRTIO_NET_F_GUEST_RSC4    41
> 
> Why not use 24?

I think we should use features >31 (virtio 1 only) for
nice-to-have features like RSC. Feature bits <31 are
easy to backport, so it makes more sense to use
them for fundamental things like the MTU
(which for some setups help fix broken networking).