Date: Mon, 17 Jun 2024 13:00:11 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>, 
	Eugenio Pérez <eperezma@...hat.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...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.dev, 
	bpf@...r.kernel.org
Subject: Re: [PATCH net-next v5 07/15] virtio_net: refactor the xmit type

On Fri, Jun 14, 2024 at 2:40 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> Because the af-xdp and sq premapped mode will introduce two
> new xmit type, so I refactor the xmit type mechanism first.
>
> We use the last two bits of the pointer to distinguish the xmit type,
> so we can distinguish four xmit types. Now we have two xmit types:
> SKB and XDP.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>  drivers/net/virtio_net.c | 58 +++++++++++++++++++++++++++-------------
>  1 file changed, 40 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 161694957065..e84a4624549b 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -47,8 +47,6 @@ module_param(napi_tx, bool, 0644);
>  #define VIRTIO_XDP_TX          BIT(0)
>  #define VIRTIO_XDP_REDIR       BIT(1)
>
> -#define VIRTIO_XDP_FLAG        BIT(0)
> -
>  /* RX packet size EWMA. The average packet size is used to determine the packet
>   * buffer size when refilling RX rings. As the entire RX ring may be refilled
>   * at once, the weight is chosen so that the EWMA will be insensitive to short-
> @@ -491,42 +489,62 @@ struct virtio_net_common_hdr {
>
>  static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf);
>
> -static bool is_xdp_frame(void *ptr)
> +enum virtnet_xmit_type {
> +       VIRTNET_XMIT_TYPE_SKB,
> +       VIRTNET_XMIT_TYPE_XDP,
> +};
> +
> +#define VIRTNET_XMIT_TYPE_MASK (VIRTNET_XMIT_TYPE_SKB | VIRTNET_XMIT_TYPE_XDP)
> +
> +static enum virtnet_xmit_type virtnet_xmit_ptr_strip(void **ptr)
>  {
> -       return (unsigned long)ptr & VIRTIO_XDP_FLAG;
> +       unsigned long p = (unsigned long)*ptr;
> +
> +       *ptr = (void *)(p & ~VIRTNET_XMIT_TYPE_MASK);
> +
> +       return p & VIRTNET_XMIT_TYPE_MASK;
>  }
>
> -static void *xdp_to_ptr(struct xdp_frame *ptr)
> +static void *virtnet_xmit_ptr_mix(void *ptr, enum virtnet_xmit_type type)

How about rename this to virtnet_ptr_to_token()?

>  {
> -       return (void *)((unsigned long)ptr | VIRTIO_XDP_FLAG);
> +       return (void *)((unsigned long)ptr | type);
>  }
>
> -static struct xdp_frame *ptr_to_xdp(void *ptr)
> +static int virtnet_add_outbuf(struct send_queue *sq, int num, void *data,
> +                             enum virtnet_xmit_type type)
>  {
> -       return (struct xdp_frame *)((unsigned long)ptr & ~VIRTIO_XDP_FLAG);
> +       return virtqueue_add_outbuf(sq->vq, sq->sg, num,
> +                                   virtnet_xmit_ptr_mix(data, type),
> +                                   GFP_ATOMIC);

Nit: I think we can just open-code this instead of using a helper.

Others look good.

Thanks


>  }
>
>  static void __free_old_xmit(struct send_queue *sq, bool in_napi,
>                             struct virtnet_sq_free_stats *stats)
>  {
> +       struct xdp_frame *frame;
> +       struct sk_buff *skb;
>         unsigned int len;
>         void *ptr;
>
>         while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
>                 ++stats->packets;
>
> -               if (!is_xdp_frame(ptr)) {
> -                       struct sk_buff *skb = ptr;
> +               switch (virtnet_xmit_ptr_strip(&ptr)) {
> +               case VIRTNET_XMIT_TYPE_SKB:
> +                       skb = ptr;
>
>                         pr_debug("Sent skb %p\n", skb);
>
>                         stats->bytes += skb->len;
>                         napi_consume_skb(skb, in_napi);
> -               } else {
> -                       struct xdp_frame *frame = ptr_to_xdp(ptr);
> +                       break;
> +
> +               case VIRTNET_XMIT_TYPE_XDP:
> +                       frame = ptr;
>
>                         stats->bytes += xdp_get_frame_len(frame);
>                         xdp_return_frame(frame);
> +                       break;
>                 }
>         }
>  }
> @@ -1064,8 +1082,7 @@ 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, xdpf, VIRTNET_XMIT_TYPE_XDP);
>         if (unlikely(err))
>                 return -ENOSPC; /* Caller handle free/refcnt */
>
> @@ -2557,7 +2574,7 @@ static int xmit_skb(struct send_queue *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, VIRTNET_XMIT_TYPE_SKB);
>  }
>
>  static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> @@ -5263,10 +5280,15 @@ 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))
> +       switch (virtnet_xmit_ptr_strip(&buf)) {
> +       case VIRTNET_XMIT_TYPE_SKB:
>                 dev_kfree_skb(buf);
> -       else
> -               xdp_return_frame(ptr_to_xdp(buf));
> +               break;
> +
> +       case VIRTNET_XMIT_TYPE_XDP:
> +               xdp_return_frame(buf);
> +               break;
> +       }
>  }
>
>  static void free_unused_bufs(struct virtnet_info *vi)
> --
> 2.32.0.3.g01195cf9f
>

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