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Subject: Re: [PATCH 0/6] virtio/vsock: introduce dgrams, sk_buff, and qdisc
CC'ing virtio-dev@lists.oasis-open.org 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/ > > 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 >
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