Subject: Re: [PATCH RFC net-next v5 00/14] virtio/vsock: support datagrams

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 27 Jul 2023 03:51:42 -0400

On Wed, Jul 19, 2023 at 12:50:04AM +0000, Bobby Eshleman wrote:
> Hey all!
> 
> This series introduces support for datagrams to virtio/vsock.
> 
> It is a spin-off (and smaller version) of this series from the summer:
>   https://lore.kernel.org/all/[email-masked]/
> 
> Please note that this is an RFC and should not be merged until
> associated changes are made to the virtio specification, which will
> follow after discussion from this series.
> 
> Another aside, the v4 of the series has only been mildly tested with a
> run of tools/testing/vsock/vsock_test. Some code likely needs cleaning
> up, but I'm hoping to get some of the design choices agreed upon before
> spending too much time making it pretty.
> 
> This series first supports datagrams in a basic form for virtio, and
> then optimizes the sendpath for all datagram transports.
> 
> The result is a very fast datagram communication protocol that
> outperforms even UDP on multi-queue virtio-net w/ vhost on a variety
> of multi-threaded workload samples.
> 
> For those that are curious, some summary data comparing UDP and VSOCK
> DGRAM (N=5):
> 
> 	vCPUS: 16
> 	virtio-net queues: 16
> 	payload size: 4KB
> 	Setup: bare metal + vm (non-nested)
> 
> 	UDP: 287.59 MB/s
> 	VSOCK DGRAM: 509.2 MB/s
> 
> Some notes about the implementation...
> 
> This datagram implementation forces datagrams to self-throttle according
> to the threshold set by sk_sndbuf. It behaves similar to the credits
> used by streams in its effect on throughput and memory consumption, but
> it is not influenced by the receiving socket as credits are.
> 
> The device drops packets silently.
> 
> As discussed previously, this series introduces datagrams and defers
> fairness to future work. See discussion in v2 for more context around
> datagrams, fairness, and this implementation.

it's a big thread - can't you summarize here?

> Signed-off-by: Bobby Eshleman <[email-masked]>

could you give a bit more motivation? which applications do
you have in mind? for example, on localhost loopback datagrams
are actually reliable and a bunch of apps came to depend
on that even if they shouldn't.

> ---
> Changes in v5:
> - teach vhost to drop dgram when a datagram exceeds the receive buffer
>   - now uses MSG_ERRQUEUE and depends on Arseniy's zerocopy patch:
> 	"vsock: read from socket's error queue"
> - replace multiple ->dgram_* callbacks with single ->dgram_addr_init()
>   callback
> - refactor virtio dgram skb allocator to reduce conflicts w/ zerocopy series
> - add _fallback/_FALLBACK suffix to dgram transport variables/macros
> - add WARN_ONCE() for table_size / VSOCK_HASH issue
> - add static to vsock_find_bound_socket_common
> - dedupe code in vsock_dgram_sendmsg() using module_got var
> - drop concurrent sendmsg() for dgram and defer to future series
> - Add more tests
>   - test EHOSTUNREACH in errqueue
>   - test stream + dgram address collision
> - improve clarity of dgram msg bounds test code
> - Link to v4: https://lore.kernel.org/r/[email-masked]
> 
> Changes in v4:
> - style changes
>   - vsock: use sk_vsock(vsk) in vsock_dgram_recvmsg instead of
>     &sk->vsk
>   - vsock: fix xmas tree declaration
>   - vsock: fix spacing issues
>   - virtio/vsock: virtio_transport_recv_dgram returns void because err
>     unused
> - sparse analysis warnings/errors
>   - virtio/vsock: fix unitialized skerr on destroy
>   - virtio/vsock: fix uninitialized err var on goto out
>   - vsock: fix declarations that need static
>   - vsock: fix __rcu annotation order
> - bugs
>   - vsock: fix null ptr in remote_info code
>   - vsock/dgram: make transport_dgram a fallback instead of first
>     priority
>   - vsock: remove redundant rcu read lock acquire in getname()
> - tests
>   - add more tests (message bounds and more)
>   - add vsock_dgram_bind() helper
>   - add vsock_dgram_connect() helper
> 
> Changes in v3:
> - Support multi-transport dgram, changing logic in connect/bind
>   to support VMCI case
> - Support per-pkt transport lookup for sendto() case
> - Fix dgram_allow() implementation
> - Fix dgram feature bit number (now it is 3)
> - Fix binding so dgram and connectible (cid,port) spaces are
>   non-overlapping
> - RCU protect transport ptr so connect() calls never leave
>   a lockless read of the transport and remote_addr are always
>   in sync
> - Link to v2: https://lore.kernel.org/r/[email-masked]
> 
> ---
> Bobby Eshleman (13):
>       af_vsock: generalize vsock_dgram_recvmsg() to all transports
>       af_vsock: refactor transport lookup code
>       af_vsock: support multi-transport datagrams
>       af_vsock: generalize bind table functions
>       af_vsock: use a separate dgram bind table
>       virtio/vsock: add VIRTIO_VSOCK_TYPE_DGRAM
>       virtio/vsock: add common datagram send path
>       af_vsock: add vsock_find_bound_dgram_socket()
>       virtio/vsock: add common datagram recv path
>       virtio/vsock: add VIRTIO_VSOCK_F_DGRAM feature bit
>       vhost/vsock: implement datagram support
>       vsock/loopback: implement datagram support
>       virtio/vsock: implement datagram support
> 
> Jiang Wang (1):
>       test/vsock: add vsock dgram tests
> 
>  drivers/vhost/vsock.c                   |  64 ++-
>  include/linux/virtio_vsock.h            |  10 +-
>  include/net/af_vsock.h                  |  14 +-
>  include/uapi/linux/virtio_vsock.h       |   2 +
>  net/vmw_vsock/af_vsock.c                | 281 ++++++++++---
>  net/vmw_vsock/hyperv_transport.c        |  13 -
>  net/vmw_vsock/virtio_transport.c        |  26 +-
>  net/vmw_vsock/virtio_transport_common.c | 190 +++++++--
>  net/vmw_vsock/vmci_transport.c          |  60 +--
>  net/vmw_vsock/vsock_loopback.c          |  10 +-
>  tools/testing/vsock/util.c              | 141 ++++++-
>  tools/testing/vsock/util.h              |   6 +
>  tools/testing/vsock/vsock_test.c        | 680 ++++++++++++++++++++++++++++++++
>  13 files changed, 1320 insertions(+), 177 deletions(-)
> ---
> base-commit: 37cadc266ebdc7e3531111c2b3304fa01b2131e8
> change-id: 20230413-b4-vsock-dgram-3b6eba6a64e5
> 
> Best regards,
> -- 
> Bobby Eshleman <[email-masked]>