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

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Bobby Eshleman <bobby.eshleman@gmail.com>
Cc: Bobby Eshleman <bobbyeshleman@gmail.com>,
	Cong Wang <cong.wang@bytedance.com>,
	Bobby Eshleman <bobby.eshleman@bytedance.com>,
	Jiang Wang <jiang.wang@bytedance.com>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	Eric Dumazet <edumazet@google.com>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	kvm@vger.kernel.org, Jakub Kicinski <kuba@kernel.org>,
	Paolo Abeni <pabeni@redhat.com>,
	"David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH 3/6] vsock: add netdev to vhost/virtio vsock
Date: Tue, 6 Sep 2022 06:58:32 -0400	[thread overview]
Message-ID: <20220906065523-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <5a93c5aad99d79f028d349cb7e3c128c65d5d7e2.1660362668.git.bobby.eshleman@bytedance.com>

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@bytedance.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

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