Re: [PATCH net-next v5 08/15] virtio_net: sq support premapped mode

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On Fri, Jun 14, 2024 at 2:39 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
>
> If the xsk is enabling, the xsk tx will share the send queue.
> But the xsk requires that the send queue use the premapped mode.
> So the send queue must support premapped mode when it is bound to
> af-xdp.
>
> * virtnet_sq_set_premapped(sq, true) is used to enable premapped mode.
>
>     In this mode, the driver will record the dma info when skb or xdp
>     frame is sent.
>
>     Currently, the SQ premapped mode is operational only with af-xdp. In
>     this mode, af-xdp, the kernel stack, and xdp tx/redirect will share
>     the same SQ. Af-xdp independently manages its DMA. The kernel stack
>     and xdp tx/redirect utilize this DMA metadata to manage the DMA
>     info.
>
>     If the indirect descriptor feature be supported, the volume of DMA
>     details we need to maintain becomes quite substantial. Here, we have
>     a cap on the amount of DMA info we manage.
>
>     If the kernel stack and xdp tx/redirect attempt to use more
>     descriptors, virtnet_add_outbuf() will return an -ENOMEM error. But
>     the af-xdp can work continually.

Rethink of this whole logic, it looks like all the complication came
as we decided to go with a pre queue pre mapping flag. I wonder if
things could be simplified if we do that per buffer?

Then we don't need complex logic like dmainfo and cap.

>
> * virtnet_sq_set_premapped(sq, false) is used to disable premapped mode.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> ---
>  drivers/net/virtio_net.c | 228 ++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 224 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index e84a4624549b..88ab9ea1646f 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -25,6 +25,7 @@
>  #include <net/net_failover.h>
>  #include <net/netdev_rx_queue.h>
>  #include <net/netdev_queues.h>
> +#include <uapi/linux/virtio_ring.h>

Why do we need this?

>
>  static int napi_weight = NAPI_POLL_WEIGHT;
>  module_param(napi_weight, int, 0444);
> @@ -276,6 +277,26 @@ struct virtnet_rq_dma {
>         u16 need_sync;
>  };
>
> +struct virtnet_sq_dma {
> +       union {
> +               struct llist_node node;
> +               struct llist_head head;

If we want to cap the #dmas, could we simply use an array instead of
the list here?

> +               void *data;
> +       };
> +       dma_addr_t addr;
> +       u32 len;
> +       u8 num;
> +};
> +
> +struct virtnet_sq_dma_info {
> +       /* record for kfree */
> +       void *p;
> +
> +       u32 free_num;
> +
> +       struct llist_head free;
> +};
> +
>  /* Internal representation of a send virtqueue */
>  struct send_queue {
>         /* Virtqueue associated with this send _queue */
> @@ -295,6 +316,11 @@ struct send_queue {
>
>         /* Record whether sq is in reset state. */
>         bool reset;
> +
> +       /* SQ is premapped mode or not. */
> +       bool premapped;
> +
> +       struct virtnet_sq_dma_info dmainfo;
>  };
>
>  /* Internal representation of a receive virtqueue */
> @@ -492,9 +518,11 @@ static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf);
>  enum virtnet_xmit_type {
>         VIRTNET_XMIT_TYPE_SKB,
>         VIRTNET_XMIT_TYPE_XDP,
> +       VIRTNET_XMIT_TYPE_DMA,

I think the name is confusing, how about TYPE_PREMAPPED?

>  };
>
> -#define VIRTNET_XMIT_TYPE_MASK (VIRTNET_XMIT_TYPE_SKB | VIRTNET_XMIT_TYPE_XDP)
> +#define VIRTNET_XMIT_TYPE_MASK (VIRTNET_XMIT_TYPE_SKB | VIRTNET_XMIT_TYPE_XDP \
> +                               | VIRTNET_XMIT_TYPE_DMA)
>
>  static enum virtnet_xmit_type virtnet_xmit_ptr_strip(void **ptr)
>  {
> @@ -510,12 +538,180 @@ static void *virtnet_xmit_ptr_mix(void *ptr, enum virtnet_xmit_type type)
>         return (void *)((unsigned long)ptr | type);
>  }
>
> +static void virtnet_sq_unmap(struct send_queue *sq, void **data)
> +{
> +       struct virtnet_sq_dma *head, *tail, *p;
> +       int i;
> +
> +       head = *data;
> +
> +       p = head;
> +
> +       for (i = 0; i < head->num; ++i) {
> +               virtqueue_dma_unmap_page_attrs(sq->vq, p->addr, p->len,
> +                                              DMA_TO_DEVICE, 0);
> +               tail = p;
> +               p = llist_entry(llist_next(&p->node), struct virtnet_sq_dma, node);
> +       }
> +
> +       *data = tail->data;
> +
> +       __llist_add_batch(&head->node, &tail->node,  &sq->dmainfo.free);
> +
> +       sq->dmainfo.free_num += head->num;
> +}
> +
> +static void *virtnet_dma_chain_update(struct send_queue *sq,
> +                                     struct virtnet_sq_dma *head,
> +                                     struct virtnet_sq_dma *tail,
> +                                     u8 num, void *data)
> +{
> +       sq->dmainfo.free_num -= num;
> +       head->num = num;
> +
> +       tail->data = data;
> +
> +       return virtnet_xmit_ptr_mix(head, VIRTNET_XMIT_TYPE_DMA);
> +}
> +
> +static struct virtnet_sq_dma *virtnet_sq_map_sg(struct send_queue *sq, int num, void *data)
> +{
> +       struct virtnet_sq_dma *head = NULL, *p = NULL;
> +       struct scatterlist *sg;
> +       dma_addr_t addr;
> +       int i, err;
> +
> +       if (num > sq->dmainfo.free_num)
> +               return NULL;
> +
> +       for (i = 0; i < num; ++i) {
> +               sg = &sq->sg[i];
> +
> +               addr = virtqueue_dma_map_page_attrs(sq->vq, sg_page(sg),
> +                                                   sg->offset,
> +                                                   sg->length, DMA_TO_DEVICE,
> +                                                   0);
> +               err = virtqueue_dma_mapping_error(sq->vq, addr);
> +               if (err)
> +                       goto err;
> +
> +               sg->dma_address = addr;
> +
> +               p = llist_entry(llist_del_first(&sq->dmainfo.free),
> +                               struct virtnet_sq_dma, node);
> +
> +               p->addr = sg->dma_address;
> +               p->len = sg->length;

I may miss something, but I don't see how we cap the total number of dmainfos.

Thanks






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