Subject: Re: [PATCH net-next v2 00/21] virtio-net: support AF_XDP zero copy

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 9 Nov 2023 03:19:04 -0500

On Tue, Nov 07, 2023 at 11:12:06AM +0800, Xuan Zhuo wrote:
> ## AF_XDP
> 
> XDP socket(AF_XDP) is an excellent bypass kernel network framework. The zero
> copy feature of xsk (XDP socket) needs to be supported by the driver. The
> performance of zero copy is very good. mlx5 and intel ixgbe already support
> this feature, This patch set allows virtio-net to support xsk's zerocopy xmit
> feature.
> 
> At present, we have completed some preparation:
> 
> 1. vq-reset (virtio spec and kernel code)
> 2. virtio-core premapped dma
> 3. virtio-net xdp refactor
> 
> So it is time for Virtio-Net to complete the support for the XDP Socket
> Zerocopy.
> 
> Virtio-net can not increase the queue num at will, so xsk shares the queue with
> kernel.
> 
> On the other hand, Virtio-Net does not support generate interrupt from driver
> manually, so when we wakeup tx xmit, we used some tips. If the CPU run by TX
> NAPI last time is other CPUs, use IPI to wake up NAPI on the remote CPU. If it
> is also the local CPU, then we wake up napi directly.
> 
> This patch set includes some refactor to the virtio-net to let that to support
> AF_XDP.
> 
> ## performance
> 
> ENV: Qemu with vhost-user(polling mode).
> Host CPU: Intel(R) Xeon(R) Platinum 8163 CPU @ 2.50GHz
> 
> ### virtio PMD in guest with testpmd
> 
> testpmd> show port stats all
> 
>  ######################## NIC statistics for port 0 ########################
>  RX-packets: 19531092064 RX-missed: 0     RX-bytes: 1093741155584
>  RX-errors: 0
>  RX-nombuf: 0
>  TX-packets: 5959955552 TX-errors: 0     TX-bytes: 371030645664
> 
> 
>  Throughput (since last show)
>  Rx-pps:   8861574     Rx-bps:  3969985208
>  Tx-pps:   8861493     Tx-bps:  3969962736
>  ############################################################################
> 
> ### AF_XDP PMD in guest with testpmd
> 
> testpmd> show port stats all
> 
>   ######################## NIC statistics for port 0  ########################
>   RX-packets: 68152727   RX-missed: 0          RX-bytes:  3816552712
>   RX-errors: 0
>   RX-nombuf:  0
>   TX-packets: 68114967   TX-errors: 33216      TX-bytes:  3814438152
> 
>   Throughput (since last show)
>   Rx-pps:      6333196          Rx-bps:   2837272088
>   Tx-pps:      6333227          Tx-bps:   2837285936
>   ############################################################################
> 
> But AF_XDP consumes more CPU for tx and rx napi(100% and 86%).
> 
> ## maintain
> 
> I am currently a reviewer for virtio-net. I commit to maintain AF_XDP support in
> virtio-net.
> 
> Please review.
> 
> Thanks.
> 
> v2
>     1. wakeup uses the way of GVE. No send ipi to wakeup napi on remote cpu.
>     2. remove rcu. Because we synchronize all operat, so the rcu is not needed.
>     3. split the commit "move to virtio_net.h" in last patch set. Just move the
>        struct/api to header when we use them.
>     4. add comments for some code
> 
> v1:
>     1. remove two virtio commits. Push this patchset to net-next
>     2. squash "virtio_net: virtnet_poll_tx support rescheduled" to xsk: support tx
>     3. fix some warnings
> 
> 
> Xuan Zhuo (21):
>   virtio_net: rename free_old_xmit_skbs to free_old_xmit
>   virtio_net: unify the code for recycling the xmit ptr
>   virtio_net: independent directory
>   virtio_net: move core structures to virtio_net.h
>   virtio_net: add prefix virtnet to all struct inside virtio_net.h
>   virtio_net: separate virtnet_rx_resize()
>   virtio_net: separate virtnet_tx_resize()
>   virtio_net: sq support premapped mode
>   virtio_net: xsk: bind/unbind xsk
>   virtio_net: xsk: prevent disable tx napi
>   virtio_net: move some api to header
>   virtio_net: xsk: tx: support tx
>   virtio_net: xsk: tx: support wakeup
>   virtio_net: xsk: tx: virtnet_free_old_xmit() distinguishes xsk buffer
>   virtio_net: xsk: tx: virtnet_sq_free_unused_buf() check xsk buffer
>   virtio_net: xsk: rx: introduce add_recvbuf_xsk()
>   virtio_net: xsk: rx: skip dma unmap when rq is bind with AF_XDP
>   virtio_net: xsk: rx: introduce receive_xsk() to recv xsk buffer
>   virtio_net: xsk: rx: virtnet_rq_free_unused_buf() check xsk buffer
>   virtio_net: update tx timeout record
>   virtio_net: xdp_features add NETDEV_XDP_ACT_XSK_ZEROCOPY
> 
>  MAINTAINERS                                 |   2 +-
>  drivers/net/Kconfig                         |   8 +-
>  drivers/net/Makefile                        |   2 +-
>  drivers/net/virtio/Kconfig                  |  13 +
>  drivers/net/virtio/Makefile                 |   8 +
>  drivers/net/{virtio_net.c => virtio/main.c} | 630 +++++++++-----------
>  drivers/net/virtio/virtio_net.h             | 346 +++++++++++
>  drivers/net/virtio/xsk.c                    | 498 ++++++++++++++++
>  drivers/net/virtio/xsk.h                    |  32 +
>  9 files changed, 1174 insertions(+), 365 deletions(-)
>  create mode 100644 drivers/net/virtio/Kconfig
>  create mode 100644 drivers/net/virtio/Makefile
>  rename drivers/net/{virtio_net.c => virtio/main.c} (92%)
>  create mode 100644 drivers/net/virtio/virtio_net.h
>  create mode 100644 drivers/net/virtio/xsk.c
>  create mode 100644 drivers/net/virtio/xsk.h

Too much code duplications for my taste. Would there maybe be less if
everything was in a single file?

> --
> 2.32.0.3.g01195cf9f