On Tue, Apr 25, 2023 at 03:36:02PM +0800, Xuan Zhuo wrote: > ## 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 by the way. I don't understand this last sentence. If you think ring reset can change device features then the answer is no, it can't. If you are saying device has to set VIRTIO_F_ACCESS_PLATFORM to benefit from this work, that's fine at least as a first approach. Note that setting VIRTIO_F_ACCESS_PLATFORM breaks old guests (it's a secirity boundary), e.g. it is not available for transitional devices. So to support transitional devices, we might want to find another way to address this down the road, but as a first step, I agree just going with DMA is fine. > 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. > > 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 (11): > virtio_ring: split: separate dma codes > virtio_ring: packed: separate dma codes > virtio_ring: packed-indirect: separate dma codes > virtio_ring: split: support premapped > virtio_ring: packed: support premapped > virtio_ring: packed-indirect: support premapped > virtio_ring: update document for virtqueue_add_* > virtio_ring: introduce virtqueue_dma_dev() > 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() > > drivers/virtio/virtio_ring.c | 352 +++++++++++++++++++++++++---------- > include/linux/virtio.h | 4 + > 2 files changed, 259 insertions(+), 97 deletions(-) > > -- > 2.32.0.3.g01195cf9f
