Re: [PATCH 0/6] virtio/vsock: introduce dgrams, sk_buff, and qdisc

[Jason Wang]

在 2022/8/17 14:54, Michael S. Tsirkin 写道:
> On Mon, Aug 15, 2022 at 10:56:03AM -0700, Bobby Eshleman wrote:
> > Hey everybody,
> >
> > This series introduces datagrams, packet scheduling, and sk_buff usage
> > to virtio vsock.
> >
> > The usage of struct sk_buff benefits users by a) preparing vsock to use
> > other related systems that require sk_buff, such as sockmap and qdisc,
> > b) supporting basic congestion control via sock_alloc_send_skb, and c)
> > reducing copying when delivering packets to TAP.
> >
> > The socket layer no longer forces errors to be -ENOMEM, as typically
> > userspace expects -EAGAIN when the sk_sndbuf threshold is reached and
> > messages are being sent with option MSG_DONTWAIT.
> >
> > The datagram work is based off previous patches by Jiang Wang[1].
> >
> > The introduction of datagrams creates a transport layer fairness issue
> > where datagrams may freely starve streams of queue access. This happens
> > because, unlike streams, datagrams lack the transactions necessary for
> > calculating credits and throttling.
> >
> > Previous proposals introduce changes to the spec to add an additional
> > virtqueue pair for datagrams[1]. Although this solution works, using
> > Linux's qdisc for packet scheduling leverages already existing systems,
> > avoids the need to change the virtio specification, and gives additional
> > capabilities. The usage of SFQ or fq_codel, for example, may solve the
> > transport layer starvation problem. It is easy to imagine other use
> > cases as well. For example, services of varying importance may be
> > assigned different priorities, and qdisc will apply appropriate
> > priority-based scheduling. By default, the system default pfifo qdisc is
> > used. The qdisc may be bypassed and legacy queuing is resumed by simply
> > setting the virtio-vsock%d network device to state DOWN. This technique
> > still allows vsock to work with zero-configuration.
> The basic question to answer then is this: with a net device qdisc
> etc in the picture, how is this different from virtio net then?
> Why do you still want to use vsock?


Or maybe it's time to revisit an old idea[1] to unify at least the 
driver part (e.g using virtio-net driver for vsock then we can all 
features that vsock is lacking now)?

Thanks

[1] 
https://lists.linuxfoundation.org/pipermail/virtualization/2018-November/039783.html


> > In summary, this series introduces these major changes to vsock:
> >
> > - virtio vsock supports datagrams
> > - virtio vsock uses struct sk_buff instead of virtio_vsock_pkt
> >    - Because virtio vsock uses sk_buff, it also uses sock_alloc_send_skb,
> >      which applies the throttling threshold sk_sndbuf.
> > - The vsock socket layer supports returning errors other than -ENOMEM.
> >    - This is used to return -EAGAIN when the sk_sndbuf threshold is
> >      reached.
> > - virtio vsock uses a net_device, through which qdisc may be used.
> >   - qdisc allows scheduling policies to be applied to vsock flows.
> >    - Some qdiscs, like SFQ, may allow vsock to avoid transport layer congestion. That is,
> >      it may avoid datagrams from flooding out stream flows. The benefit
> >      to this is that additional virtqueues are not needed for datagrams.
> >    - The net_device and qdisc is bypassed by simply setting the
> >      net_device state to DOWN.
> >
> > [1]: https://lore.kernel.org/all/20210914055440.3121004-1-jiang.wang@xxxxxxxxxxxxx/
> >
> > Bobby Eshleman (5):
> >    vsock: replace virtio_vsock_pkt with sk_buff
> >    vsock: return errors other than -ENOMEM to socket
> >    vsock: add netdev to vhost/virtio vsock
> >    virtio/vsock: add VIRTIO_VSOCK_F_DGRAM feature bit
> >    virtio/vsock: add support for dgram
> >
> > Jiang Wang (1):
> >    vsock_test: add tests for vsock dgram
> >
> >   drivers/vhost/vsock.c                   | 238 ++++----
> >   include/linux/virtio_vsock.h            |  73 ++-
> >   include/net/af_vsock.h                  |   2 +
> >   include/uapi/linux/virtio_vsock.h       |   2 +
> >   net/vmw_vsock/af_vsock.c                |  30 +-
> >   net/vmw_vsock/hyperv_transport.c        |   2 +-
> >   net/vmw_vsock/virtio_transport.c        | 237 +++++---
> >   net/vmw_vsock/virtio_transport_common.c | 771 ++++++++++++++++--------
> >   net/vmw_vsock/vmci_transport.c          |   9 +-
> >   net/vmw_vsock/vsock_loopback.c          |  51 +-
> >   tools/testing/vsock/util.c              | 105 ++++
> >   tools/testing/vsock/util.h              |   4 +
> >   tools/testing/vsock/vsock_test.c        | 195 ++++++
> >   13 files changed, 1176 insertions(+), 543 deletions(-)
> >
> > --
> > 2.35.1