netdev - Re: updated: kvm networking todo wiki

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Message-ID: <87k3mg60ww.fsf@codemonkey.ws>
Date:	Thu, 30 May 2013 08:40:47 -0500
From:	Anthony Liguori <anthony@...emonkey.ws>
To:	Stefan Hajnoczi <stefanha@...il.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>, herbert@...dor.hengli.com.au,
	kvm <kvm@...r.kernel.org>, qemu-devel <qemu-devel@...gnu.org>,
	netdev@...r.kernel.org,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	Dmitry Fleytman <dmitry@...nix.com>
Subject: Re: updated: kvm networking todo wiki

Stefan Hajnoczi <stefanha@...il.com> writes:

> On Thu, May 30, 2013 at 7:23 AM, Rusty Russell <rusty@...tcorp.com.au> wrote:
>> Anthony Liguori <anthony@...emonkey.ws> writes:
>>> Rusty Russell <rusty@...tcorp.com.au> writes:
>>>> On Fri, May 24, 2013 at 08:47:58AM -0500, Anthony Liguori wrote:
>>>>> FWIW, I think what's more interesting is using vhost-net as a networking
>>>>> backend with virtio-net in QEMU being what's guest facing.
>>>>>
>>>>> In theory, this gives you the best of both worlds: QEMU acts as a first
>>>>> line of defense against a malicious guest while still getting the
>>>>> performance advantages of vhost-net (zero-copy).
>>>>>
>>>> It would be an interesting idea if we didn't already have the vhost
>>>> model where we don't need the userspace bounce.
>>>
>>> The model is very interesting for QEMU because then we can use vhost as
>>> a backend for other types of network adapters (like vmxnet3 or even
>>> e1000).
>>>
>>> It also helps for things like fault tolerance where we need to be able
>>> to control packet flow within QEMU.
>>
>> (CC's reduced, context added, Dmitry Fleytman added for vmxnet3 thoughts).
>>
>> Then I'm really confused as to what this would look like.  A zero copy
>> sendmsg?  We should be able to implement that today.
>>
>> On the receive side, what can we do better than readv?  If we need to
>> return to userspace to tell the guest that we've got a new packet, we
>> don't win on latency.  We might reduce syscall overhead with a
>> multi-dimensional readv to read multiple packets at once?
>
> Sounds like recvmmsg(2).

Could we map this to mergable rx buffers though?

Regards,

Anthony Liguori

>
> Stefan
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