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

Jason Wang
2022-08-18T04:29:09Z

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@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