netdev - Re: [RFC] virtio-net: share receive_*() and add_recvbuf

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Date:   Tue, 16 Jul 2019 12:22:13 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [RFC] virtio-net: share receive_*() and add_recvbuf_*() with
 virtio-vsock

On Tue, Jul 16, 2019 at 06:01:33AM -0400, Michael S. Tsirkin wrote:
> On Tue, Jul 16, 2019 at 11:40:24AM +0200, Stefano Garzarella wrote:
> > On Mon, Jul 15, 2019 at 01:50:28PM -0400, Michael S. Tsirkin wrote:
> > > On Mon, Jul 15, 2019 at 09:44:16AM +0200, Stefano Garzarella wrote:
> > > > On Fri, Jul 12, 2019 at 06:14:39PM +0800, Jason Wang wrote:
> > 
> > [...]
> > 
> > > > > 
> > > > > 
> > > > > I think it's just a branch, for ethernet, go for networking stack. otherwise
> > > > > go for vsock core?
> > > > > 
> > > > 
> > > > Yes, that should work.
> > > > 
> > > > So, I should refactor the functions that can be called also from the vsock
> > > > core, in order to remove "struct net_device *dev" parameter.
> > > > Maybe creating some wrappers for the network stack.
> > > > 
> > > > Otherwise I should create a fake net_device for vsock_core.
> > > > 
> > > > What do you suggest?
> > > 
> > > Neither.
> > > 
> > > I think what Jason was saying all along is this:
> > > 
> > > virtio net doesn't actually lose packets, at least most
> > > of the time. And it actually most of the time
> > > passes all packets to host. So it's possible to use a virtio net
> > > device (possibly with a feature flag that says "does not lose packets,
> > > all packets go to host") and build vsock on top.
> > 
> > Yes, I got it after the latest Jason's reply.
> > 
> > > 
> > > and all of this is nice, but don't expect anything easy,
> > > or any quick results.
> > 
> > I expected this... :-(
> > 
> > > 
> > > Also, in a sense it's a missed opportunity: we could cut out a lot
> > > of fat and see just how fast can a protocol that is completely
> > > new and separate from networking stack go.
> > 
> > In this case, if we will try to do a PoC, what do you think is better?
> >     1. new AF_VSOCK + network-stack + virtio-net modified
> >         Maybe it is allow us to reuse a lot of stuff already written,
> >         but we will go through the network stack
> > 
> >     2. new AF_VSOCK + glue + virtio-net modified
> >         Intermediate approach, similar to Jason's proposal
> > 
> >     3, new AF_VSOCK + new virtio-vsock
> >         Can be the thinnest, but we have to rewrite many things, with the risk
> >         of making the same mistakes as the current implementation.
> > 
> 
> 1 or 3 imho. I wouldn't expect a lot from 2.  I slightly favor 3 and
> Jason 1. So take your pick :)
> 

Yes, I agree :)

Maybe "Jason 1" could be the short term (and an opportunity to study better the
code and sources of overhead) and "new AF_VSOCK + new virtio-vsock" the long
term goal with the multi-transport support in mind.

Thank you so much for your guidance and useful advice,
Stefano