netdev - Re: updated: kvm networking todo wiki

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Message-ID: <87mwrc60yd.fsf@codemonkey.ws>
Date:	Thu, 30 May 2013 08:39:54 -0500
From:	Anthony Liguori <anthony@...emonkey.ws>
To:	Rusty Russell <rusty@...tcorp.com.au>,
	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Jason Wang <jasowang@...hat.com>, herbert@...dor.hengli.com.au,
	kvm@...r.kernel.org, qemu-devel@...gnu.org, netdev@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Dmitry Fleytman <dmitry@...nix.com>
Subject: Re: updated: kvm networking todo wiki

Rusty Russell <rusty@...tcorp.com.au> writes:

> 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.

The only trouble with sendmsg would be doing batch submission and
asynchronous completion.

A thread pool could certainly be used for this I guess.

Regards,

Anthony Liguori

> 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?
>
> Confused,
> Rusty.
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