Re: [transparent networking] Re: [PATCH] kvm tools: Implement virtio network device

[Avi Kivity <avi@redhat.com>]

On 04/13/2011 04:33 PM, Avi Kivity wrote:
> On 04/13/2011 04:02 PM, Ingo Molnar wrote:
>> * Asias He<asias.hejun@gmail.com>  wrote:
>>
>> > >>  Here are some scp performance test for differenct implementations:
>> > >>  None of rx and tx as thread:
>> > >>  guest to host 3.2MB/s
>> > >>  host  to guest 3.1MB/s
>> > >>
>> > >>  Only rx as thread:
>> > >>  guest to host  14.7MB/s
>> > >>  host  to guest 33.4MB/s
>> > >>
>> > >>  Both rx and tx as thread(This patch works this way):
>> > >>  guest to host  19.8MB/s
>> > >>  host  to guest 32.5MB/s
>> > >>
>> > >>  Signed-off-by: Asias He<asias.hejun@gmail.com>
>> > >
>> > >  This is already in master. Thanks!
>> > >
>> >
>> >  Ingo suggested to CC the updated version of this patch to kvm 
>> list. So I
>> >  am posting this patch again.
>>
>> Thanks Asias, cool stuff.
>>
>> Maybe other KVM developers want to chime in about how to best implement
>> transparent (non-TAP-using) guest-side networking.
>>
>> The best approach would be to not go down as low as the IP/Ethernet 
>> packeting
>> level (it's unnecessary protocol overhead), but to implement some 
>> sort of
>> streaming, virtio based TCP connection proxying support.
>>
>> Strictly talking the guest does not need ICMP packets to have working 
>> Internet
>> connectivity - only passing/tunneling through TCP sockets would be 
>> enough. The
>> following highlevel ops are needed:
>>
>>   - connect/shutdown/close
>>   - send/receive
>>   - poll
>>
>> And would be passed through to the host side and mirrored there into 
>> real
>> connect/shutdown TCP socket ops and into send/receive ops.
>>
>> The guest OS does not need to be 'aware' of this in any way, as long 
>> as the
>> bzImage has this magic guest tunneling support included.
>>
>> Obviously, such a highlevel approach would be much faster as well 
>> than any
>> packet level virtual networking approach.
>>
>> Does something like this exist upstream, or do we have to implement it?
>>
>
> macvtap does non-privileged setupless networking.
>

But this doesn't really answer your message.  No, there is no tcp-level 
virtio device.  However, because of GSO/GRO, I don't think there is a 
huge win to be gained by bypassing the lower layers.  If you want to 
send a megabyte's worth of data into a tcp stream, you prepend a header 
and post it to virtio-net, and this goes all the way down to the real 
device.

I'm not sure tcp-offload like you propose would pass netdev@.  Similar 
approaches for real hardware were rejected since they would bypass the 
tcp stack.  Things like netfilter would no longer work.

-- 
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