On Tue, 11 Jan 2022 10:54:45 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote: > On Mon, Jan 10, 2022 at 5:59 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > > > On Fri, Jan 07, 2022 at 02:33:00PM +0800, Xuan Zhuo wrote: > > > virtqueue_add() only supports virtual addresses, dma is completed in > > > virtqueue_add(). > > > > > > In some scenarios (such as the AF_XDP scenario), DMA is completed in advance, so > > > it is necessary for us to support passing the DMA address to virtqueue_add(). > > > > > > This patch set stipulates that if sg->dma_address is not NULL, use this > > > address as the DMA address. And record this information in extra->flags, > > > which can be skipped when executing dma unmap. > > > > > > extra->flags |= VRING_DESC_F_PREDMA; > > > > > > But the indirect desc does not have a corresponding extra, so the second and > > > third patches of this patch set are to allocate the corresponding extra while > > > allocating the indirect desc. Each desc must have a corresponding extra because > > > it is possible in an sgs some are advance DMA, while others are virtual > > > addresses. So we must allocate an extra for each indirect desc. > > > > > > I didn't realize AF_XDP didn't have space to stuff the header into. > > Jason, is that expected? > > I might be wrong but it looks to me AF_XDP allows to reserve > sufficient headroom via xdp_umem_reg_v1. > I understand that there is a headroom for receiving packages, which can be used to put virtio headers. But there is no headroom defined in the direction of sending packages. I hope Magnus Karlsson can help confirm whether there is any misunderstanding. It would be best if we could not use indirect. Thanks. > > It would be best to fix that, performance is > > best if header is linear with the data ... > > This looks like a must otherwise we may meet trouble in zerocopy receive. > > Thanks > > > Or maybe we can reduce the use of indirect somewhat, at least while > > the ring is mostly empty? > > > > > Xuan Zhuo (6): > > > virtio: rename vring_unmap_state_packed() to > > > vring_unmap_extra_packed() > > > virtio: split: alloc indirect desc with extra > > > virtio: packed: alloc indirect desc with extra > > > virtio: split: virtqueue_add_split() support dma address > > > virtio: packed: virtqueue_add_packed() support dma address > > > virtio: add api virtio_dma_map() for advance dma > > > > > > drivers/virtio/virtio_ring.c | 387 ++++++++++++++++++++--------------- > > > include/linux/virtio.h | 9 + > > > 2 files changed, 232 insertions(+), 164 deletions(-) > > > > > > -- > > > 2.31.0 > > > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
