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

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Message-ID: <20090813063113.GA3508@redhat.com>
Date:	Thu, 13 Aug 2009 09:31:13 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Anthony Liguori <anthony@...emonkey.ws>
Cc:	Arnd Bergmann <arnd@...db.de>,
	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 Wed, Aug 12, 2009 at 02:27:31PM -0500, Anthony Liguori wrote:
> Arnd Bergmann wrote:
>>> As I pointed out earlier, most code in virtio net is asymmetrical: guest
>>> provides buffers, host consumes them.  Possibly, one could use virtio
>>> rings in a symmetrical way, but support of existing guest virtio net
>>> means there's almost no shared code.
>>>     
>>
>> The trick is to swap the virtqueues instead. virtio-net is actually
>> mostly symmetric in just the same way that the physical wires on a
>> twisted pair ethernet are symmetric (I like how that analogy fits).
>>   
>
> It's already been done between two guests.  See  
> http://article.gmane.org/gmane.linux.kernel.virtualization/5423
>
> Regards,
>
> Anthony Liguori

Yes, this works by copying data (see PATCH 5/5).  Another possibility is
page flipping.  Either will kill performance.

-- 
MST
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