Re: [PATCH net-next v2 08/21] virtio_net: sq support premapped mode

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

On Thu, 9 Nov 2023 14:37:38 +0800, Jason Wang <jasowang@redhat.com> wrote:
> On Tue, Nov 7, 2023 at 11:12 AM 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.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > ---
> >  drivers/net/virtio/main.c       | 163 ++++++++++++++++++++++++++++----
> >  drivers/net/virtio/virtio_net.h |  16 ++++
> >  2 files changed, 163 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/net/virtio/main.c b/drivers/net/virtio/main.c
> > index 16e75c08639e..f052db459156 100644
> > --- a/drivers/net/virtio/main.c
> > +++ b/drivers/net/virtio/main.c
> > @@ -46,6 +46,7 @@ module_param(napi_tx, bool, 0644);
> >  #define VIRTIO_XDP_REDIR       BIT(1)
> >
> >  #define VIRTIO_XDP_FLAG        BIT(0)
> > +#define VIRTIO_XMIT_DATA_MASK (VIRTIO_XDP_FLAG)
> >
> >  #define VIRTNET_DRIVER_VERSION "1.0.0"
> >
> > @@ -167,6 +168,29 @@ static struct xdp_frame *ptr_to_xdp(void *ptr)
> >         return (struct xdp_frame *)((unsigned long)ptr & ~VIRTIO_XDP_FLAG);
> >  }
> >
> > +static inline void *virtnet_sq_unmap(struct virtnet_sq *sq, void *data)
> > +{
> > +       struct virtnet_sq_dma *next, *head;
> > +
> > +       head = (void *)((unsigned long)data & ~VIRTIO_XMIT_DATA_MASK);
> > +
> > +       data = head->data;
> > +
> > +       while (head) {
> > +               virtqueue_dma_unmap_single_attrs(sq->vq, head->addr, head->len,
> > +                                                DMA_TO_DEVICE, 0);
> > +
> > +               next = head->next;
> > +
> > +               head->next = sq->dmainfo.free;
> > +               sq->dmainfo.free = head;
> > +
> > +               head = next;
> > +       }
> > +
> > +       return data;
> > +}
> > +
> >  static void __free_old_xmit(struct virtnet_sq *sq, bool in_napi,
> >                             u64 *bytes, u64 *packets)
> >  {
> > @@ -175,14 +199,24 @@ static void __free_old_xmit(struct virtnet_sq *sq, bool in_napi,
> >
> >         while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> >                 if (!is_xdp_frame(ptr)) {
> > -                       struct sk_buff *skb = ptr;
> > +                       struct sk_buff *skb;
> > +
> > +                       if (sq->do_dma)
> > +                               ptr = virtnet_sq_unmap(sq, ptr);
> > +
> > +                       skb = ptr;
> >
> >                         pr_debug("Sent skb %p\n", skb);
> >
> >                         *bytes += skb->len;
> >                         napi_consume_skb(skb, in_napi);
> >                 } else {
> > -                       struct xdp_frame *frame = ptr_to_xdp(ptr);
> > +                       struct xdp_frame *frame;
> > +
> > +                       if (sq->do_dma)
> > +                               ptr = virtnet_sq_unmap(sq, ptr);
> > +
> > +                       frame = ptr_to_xdp(ptr);
> >
> >                         *bytes += xdp_get_frame_len(frame);
> >                         xdp_return_frame(frame);
> > @@ -567,22 +601,104 @@ static void *virtnet_rq_alloc(struct virtnet_rq *rq, u32 size, gfp_t gfp)
> >         return buf;
> >  }
> >
> > -static void virtnet_rq_set_premapped(struct virtnet_info *vi)
> > +static int virtnet_sq_set_premapped(struct virtnet_sq *sq)
> >  {
> > -       int i;
> > +       struct virtnet_sq_dma *d;
> > +       int err, size, i;
> >
> > -       /* disable for big mode */
> > -       if (!vi->mergeable_rx_bufs && vi->big_packets)
> > -               return;
> > +       size = virtqueue_get_vring_size(sq->vq);
> > +
> > +       size += MAX_SKB_FRAGS + 2;
>
> Btw, the dmainfo seems per sg? If I'm correct, how can vq_size +
> MAX_SKB_FRAGS + 2 work?


We may alloc dmainfo items when the vq is full. So I prepare more dmainfo items.


>
> > +
> > +       sq->dmainfo.head = kcalloc(size, sizeof(*sq->dmainfo.head), GFP_KERNEL);
> > +       if (!sq->dmainfo.head)
> > +               return -ENOMEM;
> > +
> > +       err = virtqueue_set_dma_premapped(sq->vq);
> > +       if (err) {
> > +               kfree(sq->dmainfo.head);
> > +               return err;
> > +       }
>
> Allocating after set_dma_premapped() seems easier.

Yes. But, we donot has the way to disable premapped mode.

That is my mistake. :)


>
> Btw, is there a benchmark of TX PPS just for this patch to demonstrate
> the impact of the performance?

We will have that.


>
> > +
> > +       sq->dmainfo.free = NULL;
> > +
> > +       sq->do_dma = true;
> > +
> > +       for (i = 0; i < size; ++i) {
> > +               d = &sq->dmainfo.head[i];
> > +
> > +               d->next = sq->dmainfo.free;
> > +               sq->dmainfo.free = d;
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> > +static void virtnet_set_premapped(struct virtnet_info *vi)
> > +{
> > +       int i;
> >
> >         for (i = 0; i < vi->max_queue_pairs; i++) {
> > -               if (virtqueue_set_dma_premapped(vi->rq[i].vq))
> > -                       continue;
> > +               virtnet_sq_set_premapped(&vi->sq[i]);
> >
> > -               vi->rq[i].do_dma = true;
> > +               /* disable for big mode */
> > +               if (vi->mergeable_rx_bufs || !vi->big_packets) {
> > +                       if (!virtqueue_set_dma_premapped(vi->rq[i].vq))
> > +                               vi->rq[i].do_dma = true;
>
> How about sticking a virtnet_rq_set_premapped() and calling it here?
>
> It seems more clean.

OK.


>
> Btw, the big mode support for pre mapping is still worthwhile
> regardless whether or not XDP is supported. It has a page pool so we
> can avoid redundant DMA map/unmap there.

Yes.

I post other patch set to do this.


>
> > +               }
> >         }
> >  }
> >
> > +static struct virtnet_sq_dma *virtnet_sq_map_sg(struct virtnet_sq *sq, int nents, void *data)
> > +{
> > +       struct virtnet_sq_dma *d, *head;
> > +       struct scatterlist *sg;
> > +       int i;
> > +
> > +       head = NULL;
> > +
> > +       for_each_sg(sq->sg, sg, nents, i) {
> > +               sg->dma_address = virtqueue_dma_map_single_attrs(sq->vq, sg_virt(sg),
> > +                                                                sg->length,
> > +                                                                DMA_TO_DEVICE, 0);
> > +               if (virtqueue_dma_mapping_error(sq->vq, sg->dma_address))
> > +                       goto err;
> > +
> > +               d = sq->dmainfo.free;
> > +               sq->dmainfo.free = d->next;
> > +
> > +               d->addr = sg->dma_address;
> > +               d->len = sg->length;
> > +
> > +               d->next = head;
> > +               head = d;
> > +       }
> > +
> > +       head->data = data;
> > +
> > +       return (void *)((unsigned long)head | ((unsigned long)data & VIRTIO_XMIT_DATA_MASK));
>
> So head contains a pointer to data, any reason we still need to pack a
> data pointer here?

Maybe you are right. We can skip this.


>
>
> > +err:
> > +       virtnet_sq_unmap(sq, head);
> > +       return NULL;
> > +}
> > +
> > +static int virtnet_add_outbuf(struct virtnet_sq *sq, u32 num, void *data)
> > +{
> > +       int ret;
> > +
> > +       if (sq->do_dma) {
> > +               data = virtnet_sq_map_sg(sq, num, data);
> > +               if (!data)
> > +                       return -ENOMEM;
> > +       }
> > +
> > +       ret = virtqueue_add_outbuf(sq->vq, sq->sg, num, data, GFP_ATOMIC);
> > +       if (ret && sq->do_dma)
> > +               virtnet_sq_unmap(sq, data);
> > +
> > +       return ret;
> > +}
> > +
> >  static void free_old_xmit(struct virtnet_sq *sq, bool in_napi)
> >  {
> >         u64 bytes, packets = 0;
> > @@ -686,8 +802,7 @@ static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
> >                             skb_frag_size(frag), skb_frag_off(frag));
> >         }
> >
> > -       err = virtqueue_add_outbuf(sq->vq, sq->sg, nr_frags + 1,
> > -                                  xdp_to_ptr(xdpf), GFP_ATOMIC);
> > +       err = virtnet_add_outbuf(sq, nr_frags + 1, xdp_to_ptr(xdpf));
> >         if (unlikely(err))
> >                 return -ENOSPC; /* Caller handle free/refcnt */
> >
> > @@ -2126,7 +2241,8 @@ static int xmit_skb(struct virtnet_sq *sq, struct sk_buff *skb)
> >                         return num_sg;
> >                 num_sg++;
> >         }
> > -       return virtqueue_add_outbuf(sq->vq, sq->sg, num_sg, skb, GFP_ATOMIC);
> > +
> > +       return virtnet_add_outbuf(sq, num_sg, skb);
> >  }
> >
> >  static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> > @@ -3818,6 +3934,8 @@ static void virtnet_free_queues(struct virtnet_info *vi)
> >         for (i = 0; i < vi->max_queue_pairs; i++) {
> >                 __netif_napi_del(&vi->rq[i].napi);
> >                 __netif_napi_del(&vi->sq[i].napi);
> > +
> > +               kfree(vi->sq[i].dmainfo.head);
> >         }
> >
> >         /* We called __netif_napi_del(),
> > @@ -3866,10 +3984,23 @@ static void free_receive_page_frags(struct virtnet_info *vi)
> >
> >  static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf)
> >  {
> > -       if (!is_xdp_frame(buf))
> > +       struct virtnet_info *vi = vq->vdev->priv;
> > +       struct virtnet_sq *sq;
> > +       int i = vq2rxq(vq);
> > +
> > +       sq = &vi->sq[i];
> > +
> > +       if (!is_xdp_frame(buf)) {
> > +               if (sq->do_dma)
> > +                       buf = virtnet_sq_unmap(sq, buf);
> > +
> >                 dev_kfree_skb(buf);
> > -       else
> > +       } else {
> > +               if (sq->do_dma)
> > +                       buf = virtnet_sq_unmap(sq, buf);
> > +
> >                 xdp_return_frame(ptr_to_xdp(buf));
> > +       }
> >  }
> >
> >  static void virtnet_rq_free_unused_buf(struct virtqueue *vq, void *buf)
> > @@ -4075,7 +4206,7 @@ static int init_vqs(struct virtnet_info *vi)
> >         if (ret)
> >                 goto err_free;
> >
> > -       virtnet_rq_set_premapped(vi);
> > +       virtnet_set_premapped(vi);
> >
> >         cpus_read_lock();
> >         virtnet_set_affinity(vi);
> > diff --git a/drivers/net/virtio/virtio_net.h b/drivers/net/virtio/virtio_net.h
> > index d814341d9f97..ce806afb6d64 100644
> > --- a/drivers/net/virtio/virtio_net.h
> > +++ b/drivers/net/virtio/virtio_net.h
> > @@ -48,6 +48,18 @@ struct virtnet_rq_dma {
> >         u16 need_sync;
> >  };
> >
> > +struct virtnet_sq_dma {
> > +       struct virtnet_sq_dma *next;
> > +       dma_addr_t addr;
> > +       u32 len;
> > +       void *data;
>
> I think we need to seek a way to reuse what has been stored by virtio
> core. It should be much more efficient.


Yes.

But that is for net-next branch.

Can we do that as a fix after that is merged to 6.8?

Thanks.


>
> Thanks
>
> > +};
> > +
> > +struct virtnet_sq_dma_head {
> > +       struct virtnet_sq_dma *free;
> > +       struct virtnet_sq_dma *head;
> > +};
> > +
> >  /* Internal representation of a send virtqueue */
> >  struct virtnet_sq {
> >         /* Virtqueue associated with this virtnet_sq */
> > @@ -67,6 +79,10 @@ struct virtnet_sq {
> >
> >         /* Record whether sq is in reset state. */
> >         bool reset;
> > +
> > +       bool do_dma;
> > +
> > +       struct virtnet_sq_dma_head dmainfo;
> >  };
> >
> >  /* Internal representation of a receive virtqueue */
> > --
> > 2.32.0.3.g01195cf9f
> >
>
>