[PATCH vhost v11 00/10] virtio core prepares for AF_XDP

Xuan Zhuo
2023-07-10T03:42:27Z

## About DMA APIs

Now, virtio may can not work with DMA APIs when virtio features do not have
VIRTIO_F_ACCESS_PLATFORM.

1. I tried to let DMA APIs return phy address by virtio-device. But DMA APIs
just
   work with the "real" devices.
2. I tried to let xsk support callballs to get phy address from virtio-net
   driver as the dma address. But the maintainers of xsk may want to use dma-buf
   to replace the DMA APIs. I think that may be a larger effort. We will wait
   too long.

So rethinking this, firstly, we can support premapped-dma only for devices with
VIRTIO_F_ACCESS_PLATFORM. In the case of af-xdp, if the users want to use it,
they have to update the device to support VIRTIO_F_RING_RESET, and they can also
enable the device's VIRTIO_F_ACCESS_PLATFORM feature.

Thanks for the help from Christoph.

================
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.

ENV: Qemu with vhost.

                   vhost cpu | Guest APP CPU |Guest Softirq CPU | PPS
-----------------------------|---------------|------------------|------------
xmit by sockperf:     90%    |   100%        |                  |  318967
xmit by xsk:          100%   |   30%         |   33%            | 1192064
recv by sockperf:     100%   |   68%         |   100%           |  692288
recv by xsk:          100%   |   33%         |   43%            |  771670

Before achieving the function of Virtio-Net, we also have to let virtio core
support these features:

1. virtio core support premapped
2. virtio core support reset per-queue

================
After introducing premapping, I added an example to virtio-net. virtio-net can
merge dma mappings through this feature. @Jason


Please review.

Thanks.

v11
 1. virtio-net merges dma operates based on the feature premapped
 2. A better way to handle the map error with the premapped

v10:
 1. support to set vq to premapped mode, then the vq just handles the premapped
request.
 2. virtio-net support to do dma mapping in advance

v9:
 1. use flag to distinguish the premapped operations. no do judgment by sg.

v8:
 1. vring_sg_address: check by sg_page(sg) not dma_address. Because 0 is a valid
dma address
 2. remove unused code from vring_map_one_sg()

v7:
 1. virtqueue_dma_dev() return NULL when virtio is without DMA API.

v6:
 1. change the size of the flags to u32.

v5:
 1. fix for error handler
 2. add flags to record internal dma mapping

v4:
 1. rename map_inter to dma_map_internal
 2. fix: Excess function parameter 'vq' description in
'virtqueue_dma_dev'

v3:
 1. add map_inter to struct desc state to reocrd whether virtio core do dma map

v2:
 1. based on sgs[0]->dma_address to judgment is premapped
 2. based on extra.addr to judgment to do unmap for no-indirect desc
 3. based on indir_desc to judgment to do unmap for indirect desc
 4. rename virtqueue_get_dma_dev to virtqueue_dma_dev

v1:
 1. expose dma device. NO introduce the api for dma and sync
 2. split some commit for review.





Xuan Zhuo (10):
  virtio_ring: check use_dma_api before unmap desc for indirect
  virtio_ring: put mapping error check in vring_map_one_sg
  virtio_ring: introduce virtqueue_set_premapped()
  virtio_ring: support add premapped buf
  virtio_ring: introduce virtqueue_dma_dev()
  virtio_ring: skip unmap for premapped
  virtio_ring: correct the expression of the description of
    virtqueue_resize()
  virtio_ring: separate the logic of reset/enable from virtqueue_resize
  virtio_ring: introduce virtqueue_reset()
  virtio_net: merge dma operation for one page

 drivers/net/virtio_net.c     | 283 +++++++++++++++++++++++++++++++++--
 drivers/virtio/virtio_ring.c | 257 ++++++++++++++++++++++++-------
 include/linux/virtio.h       |   6 +
 3 files changed, 478 insertions(+), 68 deletions(-)

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2.32.0.3.g01195cf9f