Re: [Qemu-devel] idea: non-ethernet paravirtual network device

[Hannes Reinecke <hare@suse.de>]

On 07/26/2011 08:04 AM, Stefan Hajnoczi wrote:
> On Mon, Jul 25, 2011 at 4:53 PM, Sassan Panahinejad<sassan@sassan.me.uk>  wrote:
>> Here's a thought, could we improve network performance by creating a
>> paravirtual network device which doesn't emulate ethernet? It shouldn't be
>> too hard to just whack IP packets pretty much directly over a virtio link.
>> This should improve performance when using a "user" host connection and we
>> could introduce a tun host connection instead of tap for this setup.
>>
>> Does anyone have any thoughts on how worthwhile this would be? Would the
>> performance improvement justify the effort involved?
>
> My guess is no noticable impact (if you ignore ARP requests).
>
> The Ethernet header is only 14 bytes or so.  We don't calculate any
> checksums at that level.  There's probably not much of a win.
>
Only lots of pain to be had.
Mainframe used to do this. But abandoned it not, thankfully.

Problem is that you need to patch each and every tool looking at the 
packets to _not_ expecting an Ethernet header.
And patching up DHCP is _not_ trivial.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
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