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

Stefano Garzarella
2022-09-06T09:01:19Z

On Thu, Aug 18, 2022 at 12:28:48PM +0800, Jason Wang wrote:
>
>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)?

Sorry for coming late to the discussion!

This would be great, though, last time I had looked at it, I had found
it quite complicated. The main problem is trying to avoid all the
net-specific stuff (MTU, ethernet header, HW offloading, etc.).

Maybe we could start thinking about this idea by adding a new transport
to vsock (e.g. virtio-net-vsock) completely separate from what we have
now.

Thanks,
Stefano