[PATCH net-next v2 00/13] virtio-net: support AF_XDP zero copy (tx)

Xuan Zhuo
2024-10-30T08:24:57Z

v2:
1. use new api to submit premapped buffer instead of using sgs to pass this info
2. some small fixes for http://lore.kernel.org/all/20240924013204.13763-1-xuanzhuo@linux.alibaba.com

v1:
1. some small fixes for http://lore.kernel.org/all/20240820073330.9161-1-xuanzhuo@linux.alibaba.com
1. fix the title of the commit #2, #3
2. fix the gcc error for commit #3
3. use virtqueue_dma_xxxx for tx hdr
4. rename virtnet_ptr_to_xsk to virtnet_ptr_to_xsk_buff_len
5. squash #11 in last patch set to #10

================================================================================

## 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.

This patch set includes some refactor to the virtio-net to let that to support
AF_XDP.

## About virtio premapped mode

The current configuration sets the virtqueue (vq) to premapped mode,
implying that all buffers submitted to this queue must be mapped ahead
of time. This presents a challenge for the virtnet send queue (sq): the
virtnet driver would be required to keep track of dma information for vq
size * 17, which can be substantial. However, if the premapped mode were
applied on a per-buffer basis, the complexity would be greatly reduced.
With AF_XDP enabled, AF_XDP buffers would become premapped, while kernel
skb buffers could remain unmapped.

We can distinguish them by sg_page(sg), When sg_page(sg) is NULL, this
indicates that the driver has performed DMA mapping in advance, allowing
the Virtio core to directly utilize sg_dma_address(sg) without
conducting any internal DMA mapping. Additionally, DMA unmap operations
for this buffer will be bypassed.

## 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%).

Please review.

Thanks.

Xuan Zhuo (13):
virtio_ring: introduce vring_need_unmap_buffer
virtio_ring: split: record extras for indirect buffers
virtio_ring: packed: record extras for indirect buffers
virtio_ring: perform premapped operations based on per-buffer
virtio_ring: introduce add api for premapped
virtio-net: rq submits premapped per-buffer
virtio_ring: remove API virtqueue_set_dma_premapped
virtio_net: refactor the xmit type
virtio_net: xsk: bind/unbind xsk for tx
virtio_net: xsk: prevent disable tx napi
virtio_net: xsk: tx: support xmit xsk buffer
virtio_net: update tx timeout record
virtio_net: xdp_features add NETDEV_XDP_ACT_XSK_ZEROCOPY

drivers/net/virtio_net.c | 358 +++++++++++++++++++++++++++++------
drivers/virtio/virtio_ring.c | 340 ++++++++++++++++-----------------
include/linux/virtio.h | 15 +-
3 files changed, 483 insertions(+), 230 deletions(-)

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2.32.0.3.g01195cf9f