## 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
3. introduce DMA APIs to virtio core
Please review.
Thanks.
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: put mapping error check in vring_map_one_sg
virtio_ring: introduce virtqueue_set_premapped()
virtio_ring: split: support add premapped buf
virtio_ring: packed: support add premapped buf
virtio_ring: split-detach: support return dma info to driver
virtio_ring: packed-detach: support return dma info to driver
virtio_ring: introduce helpers for premapped
virtio_ring: introduce virtqueue_dma_dev()
virtio_ring: introduce virtqueue_add_sg()
virtio_net: support dma premapped
drivers/net/virtio_net.c | 163 ++++++++++--
drivers/virtio/virtio_ring.c | 493 +++++++++++++++++++++++++++++++----
include/linux/virtio.h | 34 +++
3 files changed, 612 insertions(+), 78 deletions(-)
--
2.32.0.3.g01195cf9f
