netdev - Re: [PATCH 2/2] vhost_net: a kernel-level virtio server

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Message-ID: <20090813150344.GC5080@redhat.com>
Date:	Thu, 13 Aug 2009 18:03:44 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	virtualization@...ts.linux-foundation.org,
	"Ira W. Snyder" <iws@...o.caltech.edu>, netdev@...r.kernel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] vhost_net: a kernel-level virtio server

On Thu, Aug 13, 2009 at 04:58:06PM +0200, Arnd Bergmann wrote:
> On Thursday 13 August 2009, Michael S. Tsirkin wrote:
> > > Right now, the number of copy operations in your code is the same.
> > > You are doing the copy a little bit later in skb_copy_datagram_iovec(),
> > > which is indeed a very nice hack. Changing to a virtqueue based method
> > > would imply that the host needs to add each skb_frag_t to its outbound
> > > virtqueue, which then gets copied into the guests inbound virtqueue.
> > 
> > Which is a lot more code than just calling skb_copy_datagram_iovec.
> 
> Well, I don't see this part as much of a problem, because the code
> already exists in virtio_net.

I am talking about the copying done in low level transport, here.

> If we really wanted to go down that road,
> just using virtio_net would solve the problem of frame handling
> entirely, but create new problems elsewhere, as we have mentioned.
> 
> 	Arnd <><
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