netdev - Re: [PATCH net-next v1 08/19] virtio_net: sq support premapped mode

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Date: Fri, 20 Oct 2023 14:50:52 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	"Michael S. Tsirkin" <mst@...hat.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, 
	virtualization@...ts.linux-foundation.org, bpf@...r.kernel.org
Subject: Re: [PATCH net-next v1 08/19] virtio_net: sq support premapped mode

On Mon, Oct 16, 2023 at 8:01 PM Xuan Zhuo <xuanzhuo@...ux.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@...ux.alibaba.com>
> ---
>  drivers/net/virtio/main.c       | 108 ++++++++++++++++++++++++++++----
>  drivers/net/virtio/virtio_net.h |  54 +++++++++++++++-
>  2 files changed, 149 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/net/virtio/main.c b/drivers/net/virtio/main.c
> index 8da84ea9bcbe..02d27101fef1 100644
> --- a/drivers/net/virtio/main.c
> +++ b/drivers/net/virtio/main.c
> @@ -514,20 +514,104 @@ 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;

Not specific to this patch but any plan to fix the big mode?


> +       size = virtqueue_get_vring_size(sq->vq);
> +
> +       size += MAX_SKB_FRAGS + 2;
> +
> +       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;
> +       }
> +
> +       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))
> +               if (!virtnet_sq_set_premapped(&vi->sq[i]))
> +                       vi->sq[i].do_dma = true;
> +
> +               /* disable for big mode */
> +               if (!vi->mergeable_rx_bufs && vi->big_packets)
>                         continue;
>
> -               vi->rq[i].do_dma = true;
> +               if (!virtqueue_set_dma_premapped(vi->rq[i].vq))
> +                       vi->rq[i].do_dma = true;
> +       }
> +}
> +
> +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;

It's really a pity that we need to duplicate those DMA metata twice.
Could we invent a new API to just fetch it from the virtio core?

> +       }
> +
> +       head->data = data;
> +
> +       return (void *)((unsigned long)head | ((unsigned long)data & VIRTIO_XMIT_DATA_MASK));

If we packed everything into dmainfo, we can leave the type (XDP vs
skb) there to avoid trick like packing it into the pointer here?

Thanks