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

[Xuan Zhuo <xuanzhuo@linux.alibaba.com>]

On Mon, 17 Jun 2024 13:00:13 +0800, Jason Wang <jasowang@redhat.com> wrote:
> On Fri, Jun 14, 2024 at 2:39 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> 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?

YES. That will be simply.

Then this patch will be not needed. The virtio core must record the premapped
imfo to the virtio ring state or extra.

	 http://lore.kernel.org/all/20230517022249.20790-6-xuanzhuo@linux.alibaba.com

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

So the premapped mode and the internal dma mode can coexist.
Then we do not need to make the sq to support the premapped mode.


>
> >
> > * virtnet_sq_set_premapped(sq, false) is used to disable premapped mode.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > ---
> >  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?

for using VIRTIO_RING_F_INDIRECT_DESC


>
> >
> >  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.

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);
}



Thanks.

>
> Thanks
>