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

Michael S. Tsirkin
2022-08-16T00:42:21Z

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.
>
> 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@bytedance.com/

Given this affects the driver/device interface I'd like to
ask you to please copy virtio-dev mailing list on these patches.
Subscriber only I'm afraid you will need to subscribe :(

> 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