linux-kernel - Re: [PATCH 3/6] vsock: add netdev to vhost/virtio vsock

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Date:   Tue, 6 Sep 2022 06:58:32 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Bobby Eshleman <bobby.eshleman@...il.com>
Cc:     Bobby Eshleman <bobbyeshleman@...il.com>,
        Bobby Eshleman <bobby.eshleman@...edance.com>,
        Cong Wang <cong.wang@...edance.com>,
        Jiang Wang <jiang.wang@...edance.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] vsock: add netdev to vhost/virtio vsock

On Mon, Aug 15, 2022 at 10:56:06AM -0700, Bobby Eshleman wrote:
> In order to support usage of qdisc on vsock traffic, this commit
> introduces a struct net_device to vhost and virtio vsock.
> 
> Two new devices are created, vhost-vsock for vhost and virtio-vsock
> for virtio. The devices are attached to the respective transports.
> 
> To bypass the usage of the device, the user may "down" the associated
> network interface using common tools. For example, "ip link set dev
> virtio-vsock down" lets vsock bypass the net_device and qdisc entirely,
> simply using the FIFO logic of the prior implementation.
> 
> For both hosts and guests, there is one device for all G2H vsock sockets
> and one device for all H2G vsock sockets. This makes sense for guests
> because the driver only supports a single vsock channel (one pair of
> TX/RX virtqueues), so one device and qdisc fits. For hosts, this may not
> seem ideal for some workloads. However, it is possible to use a
> multi-queue qdisc, where a given queue is responsible for a range of
> sockets. This seems to be a better solution than having one device per
> socket, which may yield a very large number of devices and qdiscs, all
> of which are dynamically being created and destroyed. Because of this
> dynamism, it would also require a complex policy management daemon, as
> devices would constantly be spun up and down as sockets were created and
> destroyed. To avoid this, one device and qdisc also applies to all H2G
> sockets.
> 
> Signed-off-by: Bobby Eshleman <bobby.eshleman@...edance.com>


I've been thinking about this generally. vsock currently
assumes reliability, but with qdisc can't we get
packet drops e.g. depending on the queueing?

What prevents user from configuring such a discipline?
One thing people like about vsock is that it's very hard
to break H2G communication even with misconfigured
networking.

-- 
MST