On Tue, 25 Apr 2023 04:13:09 -0400, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > On Tue, Apr 25, 2023 at 04:05:03PM +0800, Xuan Zhuo wrote: > > On Tue, 25 Apr 2023 03:51:47 -0400, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > > > 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. > > > > > > Sorry, I should remove "by the way". > > > > > > > > > > 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, > > > > Maybe dma-buf is a way. I'll look into it, especially some practice on xsk. > > > > > but as a first step, I agree just going with > > > DMA is fine. > > > > > > Thanks. > > Pls do make sure to disable the feature when !VIRTIO_F_ACCESS_PLATFORM > though. If you refer to the implementation inside virtio-net, this feature will depend on the return of virtqueue_dma_dev(). But virtqueue_dma_dev() depends "use_dma_api". When xen_domain() is true and !VIRTIO_F_ACCESS_PLATFORM, the "use_dma_api" is true. So what kind of situation do you mean? Thanks. > > > > > > > > > > > > > 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 > > > >
