Linux Virtualization - Jul 2019 - [RFC] virtio-net: share receive_*() and add_recvbuf_*() with virtio-vsock

On Fri, Jul 12, 2019 at 06:14:39PM +0800, Jason Wang
wrote:
> 
> On 2019/7/12 ??6:00, Stefano Garzarella wrote:
> > On Thu, Jul 11, 2019 at 03:52:21PM -0400, Michael S. Tsirkin wrote:
> > > On Thu, Jul 11, 2019 at 01:41:34PM +0200, Stefano Garzarella
wrote:
> > > > On Thu, Jul 11, 2019 at 03:37:00PM +0800, Jason Wang wrote:
> > > > > On 2019/7/10 ??11:37, Stefano Garzarella wrote:
> > > > > > Hi,
> > > > > > as Jason suggested some months ago, I looked
better at the virtio-net driver to
> > > > > > understand if we can reuse some parts also in the
virtio-vsock driver, since we
> > > > > > have similar challenges (mergeable buffers, page
allocation, small
> > > > > > packets, etc.).
> > > > > > 
> > > > > > Initially, I would add the skbuff in the
virtio-vsock in order to re-use
> > > > > > receive_*() functions.
> > > > > 
> > > > > Yes, that will be a good step.
> > > > > 
> > > > Okay, I'll go on this way.
> > > > 
> > > > > > Then I would move receive_[small, big,
mergeable]() and
> > > > > > add_recvbuf_[small, big, mergeable]() outside of
virtio-net driver, in order to
> > > > > > call them also from virtio-vsock. I need to do
some refactoring (e.g. leave the
> > > > > > XDP part on the virtio-net driver), but I think it
is feasible.
> > > > > > 
> > > > > > The idea is to create a virtio-skb.[h,c] where put
these functions and a new
> > > > > > object where stores some attributes needed (e.g.
hdr_len ) and status (e.g.
> > > > > > some fields of struct receive_queue).
> > > > > 
> > > > > My understanding is we could be more ambitious here. Do
you see any blocker
> > > > > for reusing virtio-net directly? It's better to
reuse not only the functions
> > > > > but also the logic like NAPI to avoid re-inventing
something buggy and
> > > > > duplicated.
> > > > > 
> > > > These are my concerns:
> > > > - virtio-vsock is not a "net_device", so a lot of
code related to
> > > >    ethtool, net devices (MAC address, MTU, speed, VLAN, XDP,
offloading) will be
> > > >    not used by virtio-vsock.
> 
> 
> Linux support device other than ethernet, so it should not be a problem.
> 
> 
> > > > 
> > > > - virtio-vsock has a different header. We can consider it as
part of
> > > >    virtio_net payload, but it precludes the compatibility
with old hosts. This
> > > >    was one of the major doubts that made me think about
using only the
> > > >    send/recv skbuff functions, that it shouldn't break
the compatibility.
> 
> 
> We can extend the current vnet header helper for it to work for vsock.
Okay, I'll do it.
> 
> 
> > > > 
> > > > > > This is an idea of virtio-skb.h that
> > > > > > I have in mind:
> > > > > >       struct virtskb;
> > > > > 
> > > > > What fields do you want to store in virtskb? It looks
to be exist sk_buff is
> > > > > flexible enough to us?
> > > > My idea is to store queues information, like struct
receive_queue or
> > > > struct send_queue, and some device attributes (e.g. hdr_len
).
> 
> 
> If you reuse skb or virtnet_info, there is not necessary.
> 
Okay.
> 
> > > > 
> > > > > 
> > > > > >       struct sk_buff *virtskb_receive_small(struct
virtskb *vs, ...);
> > > > > >       struct sk_buff *virtskb_receive_big(struct
virtskb *vs, ...);
> > > > > >       struct sk_buff
*virtskb_receive_mergeable(struct virtskb *vs, ...);
> > > > > > 
> > > > > >       int virtskb_add_recvbuf_small(struct
virtskb*vs, ...);
> > > > > >       int virtskb_add_recvbuf_big(struct virtskb
*vs, ...);
> > > > > >       int virtskb_add_recvbuf_mergeable(struct
virtskb *vs, ...);
> > > > > > 
> > > > > > For the Guest->Host path it should be easier,
so maybe I can add a
> > > > > > "virtskb_send(struct virtskb *vs, struct
sk_buff *skb)" with a part of the code
> > > > > > of xmit_skb().
> > > > > 
> > > > > I may miss something, but I don't see any thing
that prevents us from using
> > > > > xmit_skb() directly.
> > > > > 
> > > > Yes, but my initial idea was to make it more parametric and
not related to the
> > > > virtio_net_hdr, so the 'hdr_len' could be a
parameter and the
> > > > 'num_buffers' should be handled by the caller.
> > > > 
> > > > > > Let me know if you have in mind better names or if
I should put these function
> > > > > > in another place.
> > > > > > 
> > > > > > I would like to leave the control part completely
separate, so, for example,
> > > > > > the two drivers will negotiate the features
independently and they will call
> > > > > > the right virtskb_receive_*() function based on
the negotiation.
> > > > > 
> > > > > If it's one the issue of negotiation, we can simply
change the
> > > > > virtnet_probe() to deal with different devices.
> > > > > 
> > > > > 
> > > > > > I already started to work on it, but before to do
more steps and send an RFC
> > > > > > patch, I would like to hear your opinion.
> > > > > > Do you think that makes sense?
> > > > > > Do you see any issue or a better solution?
> > > > > 
> > > > > I still think we need to seek a way of adding some
codes on virtio-net.c
> > > > > directly if there's no huge different in the
processing of TX/RX. That would
> > > > > save us a lot time.
> > > > After the reading of the buffers from the virtqueue I think
the process
> > > > is slightly different, because virtio-net will interface
with the network
> > > > stack, while virtio-vsock will interface with the vsock-core
(socket).
> > > > So the virtio-vsock implements the following:
> > > > - control flow mechanism to avoid to loose packets,
informing the peer
> > > >    about the amount of memory available in the receive queue
using some
> > > >    fields in the virtio_vsock_hdr
> > > > - de-multiplexing parsing the virtio_vsock_hdr and choosing
the right
> > > >    socket depending on the port
> > > > - socket state handling
> 
> 
> 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?
> 
> > > > 
> > > > We can use the virtio-net as transport, but we should add a
lot of
> > > > code to skip "net device" stuff when it is used by
the virtio-vsock.
> 
> 
> This could be another choice, but consider it was not transparent to the
> admin and require new features, we may seek a transparent solution here.
> 
> 
> > > > This could break something in virtio-net, for this reason, I
thought to reuse
> > > > only the send/recv functions starting from the idea to split
the virtio-net
> > > > driver in two parts:
> > > > a. one with all stuff related to the network stack
> > > > b. one with the stuff needed to communicate with the host
> > > > 
> > > > And use skbuff to communicate between parts. In this way,
virtio-vsock
> > > > can use only the b part.
> > > > 
> > > > Maybe we can do this split in a better way, but I'm not
sure it is
> > > > simple.
> > > > 
> > > > Thanks,
> > > > Stefano
> > > Frankly, skb is a huge structure which adds a lot of
> > > overhead. I am not sure that using it is such a great idea
> > > if building a device that does not have to interface
> > > with the networking stack.
> 
> 
> I believe vsock is mainly used for stream performance not for PPS. So the
> impact should be minimal. We can use other metadata, just need branch in
> recv_xxx().
> 
Yes, I think stream performance is the case.
> 
> > Thanks for the advice!
> > 
> > > So I agree with Jason in theory. To clarify, he is basically
saying
> > > current implementation is all wrong, it should be a protocol and
we
> > > should teach networking stack that there are reliable net devices
that
> > > handle just this protocol. We could add a flag in virtio net that
> > > will say it's such a device.
> > > 
> > > Whether it's doable, I don't know, and it's
definitely not simple - in
> > > particular you will have to also re-implement existing devices in
these
> > > terms, and not just virtio - vmware vsock too.
> 
> 
> Merging vsock protocol to exist networking stack could be a long term goal,
> I believe for the first phase, we can seek to use virtio-net first.
>
Yes, I agree.
> 
> > > 
> > > If you want to do a POC you can add a new address family,
> > > that's easier.
> > Very interesting!
> > I agree with you. In this way we can completely split the protocol
> > logic, from the device.
> > 
> > As you said, it will not simple to do, but can be an opportunity to
learn
> > better the Linux networking stack!
> > I'll try to do a PoC with AF_VSOCK2 that will use the virtio-net.
> 
> 
> I suggest to do this step by step:
> 
> 1) use virtio-net but keep some protocol logic
> 
> 2) separate protocol logic and merge it to exist Linux networking stack
Make sense, thanks for the suggestions, I'll try to do these steps!

Thanks,
Stefano

>>>>>>>        struct sk_buff *virtskb_receive_small(struct
virtskb *vs, ...);
>>>>>>>        struct sk_buff *virtskb_receive_big(struct
virtskb *vs, ...);
>>>>>>>        struct sk_buff
*virtskb_receive_mergeable(struct virtskb *vs, ...);
>>>>>>>
>>>>>>>        int virtskb_add_recvbuf_small(struct
virtskb*vs, ...);
>>>>>>>        int virtskb_add_recvbuf_big(struct virtskb
*vs, ...);
>>>>>>>        int virtskb_add_recvbuf_mergeable(struct
virtskb *vs, ...);
>>>>>>>
>>>>>>> For the Guest->Host path it should be easier, so
maybe I can add a
>>>>>>> "virtskb_send(struct virtskb *vs, struct
sk_buff *skb)" with a part of the code
>>>>>>> of xmit_skb().
>>>>>> I may miss something, but I don't see any thing
that prevents us from using
>>>>>> xmit_skb() directly.
>>>>>>
>>>>> Yes, but my initial idea was to make it more parametric and
not related to the
>>>>> virtio_net_hdr, so the 'hdr_len' could be a
parameter and the
>>>>> 'num_buffers' should be handled by the caller.
>>>>>
>>>>>>> Let me know if you have in mind better names or if
I should put these function
>>>>>>> in another place.
>>>>>>>
>>>>>>> I would like to leave the control part completely
separate, so, for example,
>>>>>>> the two drivers will negotiate the features
independently and they will call
>>>>>>> the right virtskb_receive_*() function based on the
negotiation.
>>>>>> If it's one the issue of negotiation, we can simply
change the
>>>>>> virtnet_probe() to deal with different devices.
>>>>>>
>>>>>>
>>>>>>> I already started to work on it, but before to do
more steps and send an RFC
>>>>>>> patch, I would like to hear your opinion.
>>>>>>> Do you think that makes sense?
>>>>>>> Do you see any issue or a better solution?
>>>>>> I still think we need to seek a way of adding some
codes on virtio-net.c
>>>>>> directly if there's no huge different in the
processing of TX/RX. That would
>>>>>> save us a lot time.
>>>>> After the reading of the buffers from the virtqueue I think
the process
>>>>> is slightly different, because virtio-net will interface
with the network
>>>>> stack, while virtio-vsock will interface with the
vsock-core (socket).
>>>>> So the virtio-vsock implements the following:
>>>>> - control flow mechanism to avoid to loose packets,
informing the peer
>>>>>     about the amount of memory available in the receive
queue using some
>>>>>     fields in the virtio_vsock_hdr
>>>>> - de-multiplexing parsing the virtio_vsock_hdr and choosing
the right
>>>>>     socket depending on the port
>>>>> - socket state handling
>>
>> 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?

I'm not quite sure I get the question. Can you just use the one that 
created by virtio_net?


Thanks

On Mon, Jul 15, 2019 at 05:16:09PM +0800, Jason Wang
wrote:
> 
> > > > > > > >        struct sk_buff
*virtskb_receive_small(struct virtskb *vs, ...);
> > > > > > > >        struct sk_buff
*virtskb_receive_big(struct virtskb *vs, ...);
> > > > > > > >        struct sk_buff
*virtskb_receive_mergeable(struct virtskb *vs, ...);
> > > > > > > > 
> > > > > > > >        int
virtskb_add_recvbuf_small(struct virtskb*vs, ...);
> > > > > > > >        int
virtskb_add_recvbuf_big(struct virtskb *vs, ...);
> > > > > > > >        int
virtskb_add_recvbuf_mergeable(struct virtskb *vs, ...);
> > > > > > > > 
> > > > > > > > For the Guest->Host path it should be
easier, so maybe I can add a
> > > > > > > > "virtskb_send(struct virtskb *vs,
struct sk_buff *skb)" with a part of the code
> > > > > > > > of xmit_skb().
> > > > > > > I may miss something, but I don't see any
thing that prevents us from using
> > > > > > > xmit_skb() directly.
> > > > > > > 
> > > > > > Yes, but my initial idea was to make it more
parametric and not related to the
> > > > > > virtio_net_hdr, so the 'hdr_len' could be
a parameter and the
> > > > > > 'num_buffers' should be handled by the
caller.
> > > > > > 
> > > > > > > > Let me know if you have in mind better
names or if I should put these function
> > > > > > > > in another place.
> > > > > > > > 
> > > > > > > > I would like to leave the control part
completely separate, so, for example,
> > > > > > > > the two drivers will negotiate the
features independently and they will call
> > > > > > > > the right virtskb_receive_*() function
based on the negotiation.
> > > > > > > If it's one the issue of negotiation, we
can simply change the
> > > > > > > virtnet_probe() to deal with different
devices.
> > > > > > > 
> > > > > > > 
> > > > > > > > I already started to work on it, but
before to do more steps and send an RFC
> > > > > > > > patch, I would like to hear your
opinion.
> > > > > > > > Do you think that makes sense?
> > > > > > > > Do you see any issue or a better
solution?
> > > > > > > I still think we need to seek a way of adding
some codes on virtio-net.c
> > > > > > > directly if there's no huge different in
the processing of TX/RX. That would
> > > > > > > save us a lot time.
> > > > > > After the reading of the buffers from the
virtqueue I think the process
> > > > > > is slightly different, because virtio-net will
interface with the network
> > > > > > stack, while virtio-vsock will interface with the
vsock-core (socket).
> > > > > > So the virtio-vsock implements the following:
> > > > > > - control flow mechanism to avoid to loose
packets, informing the peer
> > > > > >     about the amount of memory available in the
receive queue using some
> > > > > >     fields in the virtio_vsock_hdr
> > > > > > - de-multiplexing parsing the virtio_vsock_hdr and
choosing the right
> > > > > >     socket depending on the port
> > > > > > - socket state handling
> > > 
> > > 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?
> 
> 
> I'm not quite sure I get the question. Can you just use the one that
created
> by virtio_net?
Sure, sorry but I missed that it is allocated in the virtnet_probe()!

Thanks,
Stefano

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:
> > 
> > On 2019/7/12 ??6:00, Stefano Garzarella wrote:
> > > On Thu, Jul 11, 2019 at 03:52:21PM -0400, Michael S. Tsirkin
wrote:
> > > > On Thu, Jul 11, 2019 at 01:41:34PM +0200, Stefano Garzarella
wrote:
> > > > > On Thu, Jul 11, 2019 at 03:37:00PM +0800, Jason Wang
wrote:
> > > > > > On 2019/7/10 ??11:37, Stefano Garzarella wrote:
> > > > > > > Hi,
> > > > > > > as Jason suggested some months ago, I looked
better at the virtio-net driver to
> > > > > > > understand if we can reuse some parts also in
the virtio-vsock driver, since we
> > > > > > > have similar challenges (mergeable buffers,
page allocation, small
> > > > > > > packets, etc.).
> > > > > > > 
> > > > > > > Initially, I would add the skbuff in the
virtio-vsock in order to re-use
> > > > > > > receive_*() functions.
> > > > > > 
> > > > > > Yes, that will be a good step.
> > > > > > 
> > > > > Okay, I'll go on this way.
> > > > > 
> > > > > > > Then I would move receive_[small, big,
mergeable]() and
> > > > > > > add_recvbuf_[small, big, mergeable]() outside
of virtio-net driver, in order to
> > > > > > > call them also from virtio-vsock. I need to
do some refactoring (e.g. leave the
> > > > > > > XDP part on the virtio-net driver), but I
think it is feasible.
> > > > > > > 
> > > > > > > The idea is to create a virtio-skb.[h,c]
where put these functions and a new
> > > > > > > object where stores some attributes needed
(e.g. hdr_len ) and status (e.g.
> > > > > > > some fields of struct receive_queue).
> > > > > > 
> > > > > > My understanding is we could be more ambitious
here. Do you see any blocker
> > > > > > for reusing virtio-net directly? It's better
to reuse not only the functions
> > > > > > but also the logic like NAPI to avoid re-inventing
something buggy and
> > > > > > duplicated.
> > > > > > 
> > > > > These are my concerns:
> > > > > - virtio-vsock is not a "net_device", so a
lot of code related to
> > > > >    ethtool, net devices (MAC address, MTU, speed, VLAN,
XDP, offloading) will be
> > > > >    not used by virtio-vsock.
> > 
> > 
> > Linux support device other than ethernet, so it should not be a
problem.
> > 
> > 
> > > > > 
> > > > > - virtio-vsock has a different header. We can consider
it as part of
> > > > >    virtio_net payload, but it precludes the
compatibility with old hosts. This
> > > > >    was one of the major doubts that made me think about
using only the
> > > > >    send/recv skbuff functions, that it shouldn't
break the compatibility.
> > 
> > 
> > We can extend the current vnet header helper for it to work for vsock.
> 
> Okay, I'll do it.
> 
> > 
> > 
> > > > > 
> > > > > > > This is an idea of virtio-skb.h that
> > > > > > > I have in mind:
> > > > > > >       struct virtskb;
> > > > > > 
> > > > > > What fields do you want to store in virtskb? It
looks to be exist sk_buff is
> > > > > > flexible enough to us?
> > > > > My idea is to store queues information, like struct
receive_queue or
> > > > > struct send_queue, and some device attributes (e.g.
hdr_len ).
> > 
> > 
> > If you reuse skb or virtnet_info, there is not necessary.
> > 
> 
> Okay.
> 
> > 
> > > > > 
> > > > > > 
> > > > > > >       struct sk_buff
*virtskb_receive_small(struct virtskb *vs, ...);
> > > > > > >       struct sk_buff
*virtskb_receive_big(struct virtskb *vs, ...);
> > > > > > >       struct sk_buff
*virtskb_receive_mergeable(struct virtskb *vs, ...);
> > > > > > > 
> > > > > > >       int virtskb_add_recvbuf_small(struct
virtskb*vs, ...);
> > > > > > >       int virtskb_add_recvbuf_big(struct
virtskb *vs, ...);
> > > > > > >       int
virtskb_add_recvbuf_mergeable(struct virtskb *vs, ...);
> > > > > > > 
> > > > > > > For the Guest->Host path it should be
easier, so maybe I can add a
> > > > > > > "virtskb_send(struct virtskb *vs, struct
sk_buff *skb)" with a part of the code
> > > > > > > of xmit_skb().
> > > > > > 
> > > > > > I may miss something, but I don't see any
thing that prevents us from using
> > > > > > xmit_skb() directly.
> > > > > > 
> > > > > Yes, but my initial idea was to make it more parametric
and not related to the
> > > > > virtio_net_hdr, so the 'hdr_len' could be a
parameter and the
> > > > > 'num_buffers' should be handled by the caller.
> > > > > 
> > > > > > > Let me know if you have in mind better names
or if I should put these function
> > > > > > > in another place.
> > > > > > > 
> > > > > > > I would like to leave the control part
completely separate, so, for example,
> > > > > > > the two drivers will negotiate the features
independently and they will call
> > > > > > > the right virtskb_receive_*() function based
on the negotiation.
> > > > > > 
> > > > > > If it's one the issue of negotiation, we can
simply change the
> > > > > > virtnet_probe() to deal with different devices.
> > > > > > 
> > > > > > 
> > > > > > > I already started to work on it, but before
to do more steps and send an RFC
> > > > > > > patch, I would like to hear your opinion.
> > > > > > > Do you think that makes sense?
> > > > > > > Do you see any issue or a better solution?
> > > > > > 
> > > > > > I still think we need to seek a way of adding some
codes on virtio-net.c
> > > > > > directly if there's no huge different in the
processing of TX/RX. That would
> > > > > > save us a lot time.
> > > > > After the reading of the buffers from the virtqueue I
think the process
> > > > > is slightly different, because virtio-net will
interface with the network
> > > > > stack, while virtio-vsock will interface with the
vsock-core (socket).
> > > > > So the virtio-vsock implements the following:
> > > > > - control flow mechanism to avoid to loose packets,
informing the peer
> > > > >    about the amount of memory available in the receive
queue using some
> > > > >    fields in the virtio_vsock_hdr
> > > > > - de-multiplexing parsing the virtio_vsock_hdr and
choosing the right
> > > > >    socket depending on the port
> > > > > - socket state handling
> > 
> > 
> > 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.

and all of this is nice, but don't expect anything easy,
or any quick results.

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.
Instead vsock implementation carries so much baggage from both
networking stack - such as softirq processing - and itself such as
workqueues, global state and crude locking - to the point where
it's actually slower than TCP.
> > 
> > > > > 
> > > > > We can use the virtio-net as transport, but we should
add a lot of
> > > > > code to skip "net device" stuff when it is
used by the virtio-vsock.
> > 
> > 
> > This could be another choice, but consider it was not transparent to
the
> > admin and require new features, we may seek a transparent solution
here.
> > 
> > 
> > > > > This could break something in virtio-net, for this
reason, I thought to reuse
> > > > > only the send/recv functions starting from the idea to
split the virtio-net
> > > > > driver in two parts:
> > > > > a. one with all stuff related to the network stack
> > > > > b. one with the stuff needed to communicate with the
host
> > > > > 
> > > > > And use skbuff to communicate between parts. In this
way, virtio-vsock
> > > > > can use only the b part.
> > > > > 
> > > > > Maybe we can do this split in a better way, but I'm
not sure it is
> > > > > simple.
> > > > > 
> > > > > Thanks,
> > > > > Stefano
> > > > Frankly, skb is a huge structure which adds a lot of
> > > > overhead. I am not sure that using it is such a great idea
> > > > if building a device that does not have to interface
> > > > with the networking stack.
> > 
> > 
> > I believe vsock is mainly used for stream performance not for PPS. So
the
> > impact should be minimal. We can use other metadata, just need branch
in
> > recv_xxx().
> > 
> 
> Yes, I think stream performance is the case.
> 
> > 
> > > Thanks for the advice!
> > > 
> > > > So I agree with Jason in theory. To clarify, he is basically
saying
> > > > current implementation is all wrong, it should be a protocol
and we
> > > > should teach networking stack that there are reliable net
devices that
> > > > handle just this protocol. We could add a flag in virtio net
that
> > > > will say it's such a device.
> > > > 
> > > > Whether it's doable, I don't know, and it's
definitely not simple - in
> > > > particular you will have to also re-implement existing
devices in these
> > > > terms, and not just virtio - vmware vsock too.
> > 
> > 
> > Merging vsock protocol to exist networking stack could be a long term
goal,
> > I believe for the first phase, we can seek to use virtio-net first.
> >
> 
> Yes, I agree.
> 
> > 
> > > > 
> > > > If you want to do a POC you can add a new address family,
> > > > that's easier.
> > > Very interesting!
> > > I agree with you. In this way we can completely split the
protocol
> > > logic, from the device.
> > > 
> > > As you said, it will not simple to do, but can be an opportunity
to learn
> > > better the Linux networking stack!
> > > I'll try to do a PoC with AF_VSOCK2 that will use the
virtio-net.
> > 
> > 
> > I suggest to do this step by step:
> > 
> > 1) use virtio-net but keep some protocol logic
> > 
> > 2) separate protocol logic and merge it to exist Linux networking
stack
> 
> Make sense, thanks for the suggestions, I'll try to do these steps!
> 
> Thanks,
> Stefano

An alternative is look at sources of overhead in vsock and get rid of
them, or rewrite it from scratch focusing on performance.


-- 
MST

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.

> Instead vsock implementation carries so much baggage from both
> networking stack - such as softirq processing - and itself such as
> workqueues, global state and crude locking - to the point where
> it's actually slower than TCP.
I agree, and I'm finding new issues while I'm trying to support nested
VMs, allowing multiple vsock transports (virtio-vsock and vhost-vsock in
the KVM case) at runtime.
> 
[...]
> > > 
> > > I suggest to do this step by step:
> > > 
> > > 1) use virtio-net but keep some protocol logic
> > > 
> > > 2) separate protocol logic and merge it to exist Linux networking
stack
> > 
> > Make sense, thanks for the suggestions, I'll try to do these
steps!
> > 
> > Thanks,
> > Stefano
> 
> 
> An alternative is look at sources of overhead in vsock and get rid of
> them, or rewrite it from scratch focusing on performance.
I started looking at virtio-vsock and vhost-vsock trying to do very
simple changes [1] to increase the performance. I should send a v4 of that
series as a very short term, then I'd like to have a deeper look to
understand
if it is better to try to optimize or rewrite it from scratch.


Thanks,
Stefano

[1] https://patchwork.kernel.org/cover/10970145/