Re: [PATCH net-next v6 08/10] virtio_net: xsk: rx: support recv small mode

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

On Mon, 1 Jul 2024 11:25:37 +0800, Jason Wang <jasowang@redhat.com> wrote:
> On Mon, Jul 1, 2024 at 11:20 AM Jason Wang <jasowang@redhat.com> wrote:
> >
> > On Fri, Jun 28, 2024 at 1:48 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> > >
> > > On Fri, 28 Jun 2024 10:19:41 +0800, Jason Wang <jasowang@redhat.com> wrote:
> > > > On Tue, Jun 18, 2024 at 3:57 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> > > > >
> > > > > In the process:
> > > > > 1. We may need to copy data to create skb for XDP_PASS.
> > > > > 2. We may need to call xsk_buff_free() to release the buffer.
> > > > > 3. The handle for xdp_buff is difference from the buffer.
> > > > >
> > > > > If we pushed this logic into existing receive handle(merge and small),
> > > > > we would have to maintain code scattered inside merge and small (and big).
> > > > > So I think it is a good choice for us to put the xsk code into an
> > > > > independent function.
> > > >
> > > > I think it's better to try to reuse the existing functions.
> > > >
> > > > More below:
> > > >
> > > > >
> > > > > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > > > > ---
> > > > >  drivers/net/virtio_net.c | 135 ++++++++++++++++++++++++++++++++++++++-
> > > > >  1 file changed, 133 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > > > index 2ac5668a94ce..06608d696e2e 100644
> > > > > --- a/drivers/net/virtio_net.c
> > > > > +++ b/drivers/net/virtio_net.c
> > > > > @@ -500,6 +500,10 @@ struct virtio_net_common_hdr {
> > > > >  };
> > > > >
> > > > >  static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf);
> > > > > +static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
> > > > > +                              struct net_device *dev,
> > > > > +                              unsigned int *xdp_xmit,
> > > > > +                              struct virtnet_rq_stats *stats);
> > > > >
> > > > >  static bool is_xdp_frame(void *ptr)
> > > > >  {
> > > > > @@ -1040,6 +1044,120 @@ static void sg_fill_dma(struct scatterlist *sg, dma_addr_t addr, u32 len)
> > > > >         sg->length = len;
> > > > >  }
> > > > >
> > > > > +static struct xdp_buff *buf_to_xdp(struct virtnet_info *vi,
> > > > > +                                  struct receive_queue *rq, void *buf, u32 len)
> > > > > +{
> > > > > +       struct xdp_buff *xdp;
> > > > > +       u32 bufsize;
> > > > > +
> > > > > +       xdp = (struct xdp_buff *)buf;
> > > > > +
> > > > > +       bufsize = xsk_pool_get_rx_frame_size(rq->xsk.pool) + vi->hdr_len;
> > > > > +
> > > > > +       if (unlikely(len > bufsize)) {
> > > > > +               pr_debug("%s: rx error: len %u exceeds truesize %u\n",
> > > > > +                        vi->dev->name, len, bufsize);
> > > > > +               DEV_STATS_INC(vi->dev, rx_length_errors);
> > > > > +               xsk_buff_free(xdp);
> > > > > +               return NULL;
> > > > > +       }
> > > > > +
> > > > > +       xsk_buff_set_size(xdp, len);
> > > > > +       xsk_buff_dma_sync_for_cpu(xdp);
> > > > > +
> > > > > +       return xdp;
> > > > > +}
> > > > > +
> > > > > +static struct sk_buff *xdp_construct_skb(struct receive_queue *rq,
> > > > > +                                        struct xdp_buff *xdp)
> > > > > +{
> > > >
> > > > So we have a similar caller which is receive_small_build_skb(). Any
> > > > chance to reuse that?
> > >
> > > receive_small_build_skb works with build_skb.
> >
> > RIght.
> >
> > >
> > > Here we need to copy the packet from the xsk buffer to the skb buffer.
> > > So I do not think we can reuse it.
> > >
> >
> > Let's rename this to xsk_construct_skb() ?
> >
> > >
> > > >
> > > > > +       unsigned int metasize = xdp->data - xdp->data_meta;
> > > > > +       struct sk_buff *skb;
> > > > > +       unsigned int size;
> > > > > +
> > > > > +       size = xdp->data_end - xdp->data_hard_start;
> > > > > +       skb = napi_alloc_skb(&rq->napi, size);
> > > > > +       if (unlikely(!skb)) {
> > > > > +               xsk_buff_free(xdp);
> > > > > +               return NULL;
> > > > > +       }
> > > > > +
> > > > > +       skb_reserve(skb, xdp->data_meta - xdp->data_hard_start);
> > > > > +
> > > > > +       size = xdp->data_end - xdp->data_meta;
> > > > > +       memcpy(__skb_put(skb, size), xdp->data_meta, size);
> > > > > +
> > > > > +       if (metasize) {
> > > > > +               __skb_pull(skb, metasize);
> > > > > +               skb_metadata_set(skb, metasize);
> > > > > +       }
> > > > > +
> > > > > +       xsk_buff_free(xdp);
> > > > > +
> > > > > +       return skb;
> > > > > +}
> > > > > +
> > > > > +static struct sk_buff *virtnet_receive_xsk_small(struct net_device *dev, struct virtnet_info *vi,
> > > > > +                                                struct receive_queue *rq, struct xdp_buff *xdp,
> > > > > +                                                unsigned int *xdp_xmit,
> > > > > +                                                struct virtnet_rq_stats *stats)
> > > > > +{
> > > > > +       struct bpf_prog *prog;
> > > > > +       u32 ret;
> > > > > +
> > > > > +       ret = XDP_PASS;
> > > > > +       rcu_read_lock();
> > > > > +       prog = rcu_dereference(rq->xdp_prog);
> > > > > +       if (prog)
> > > > > +               ret = virtnet_xdp_handler(prog, xdp, dev, xdp_xmit, stats);
> > > > > +       rcu_read_unlock();
> > > > > +
> > > > > +       switch (ret) {
> > > > > +       case XDP_PASS:
> > > > > +               return xdp_construct_skb(rq, xdp);
> > > > > +
> > > > > +       case XDP_TX:
> > > > > +       case XDP_REDIRECT:
> > > > > +               return NULL;
> > > > > +
> > > > > +       default:
> > > > > +               /* drop packet */
> > > > > +               xsk_buff_free(xdp);
> > > > > +               u64_stats_inc(&stats->drops);
> > > > > +               return NULL;
> > > > > +       }
> > > > > +}
> > > > > +
> > > > > +static struct sk_buff *virtnet_receive_xsk_buf(struct virtnet_info *vi, struct receive_queue *rq,
> > > > > +                                              void *buf, u32 len,
> > > > > +                                              unsigned int *xdp_xmit,
> > > > > +                                              struct virtnet_rq_stats *stats)
> > > > > +{
> > > > > +       struct net_device *dev = vi->dev;
> > > > > +       struct sk_buff *skb = NULL;
> > > > > +       struct xdp_buff *xdp;
> > > > > +
> > > > > +       len -= vi->hdr_len;
> > > > > +
> > > > > +       u64_stats_add(&stats->bytes, len);
> > > > > +
> > > > > +       xdp = buf_to_xdp(vi, rq, buf, len);
> > > > > +       if (!xdp)
> > > > > +               return NULL;
> > > > > +
> > > > > +       if (unlikely(len < ETH_HLEN)) {
> > > > > +               pr_debug("%s: short packet %i\n", dev->name, len);
> > > > > +               DEV_STATS_INC(dev, rx_length_errors);
> > > > > +               xsk_buff_free(xdp);
> > > > > +               return NULL;
> > > > > +       }
> > > > > +
> > > > > +       if (!vi->mergeable_rx_bufs)
> > > > > +               skb = virtnet_receive_xsk_small(dev, vi, rq, xdp, xdp_xmit, stats);
> > > > > +
> > > > > +       return skb;
> > > > > +}
> > > > > +
> > > > >  static int virtnet_add_recvbuf_xsk(struct virtnet_info *vi, struct receive_queue *rq,
> > > > >                                    struct xsk_buff_pool *pool, gfp_t gfp)
> > > > >  {
> > > > > @@ -2363,9 +2481,22 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
> > > > >         void *buf;
> > > > >         int i;
> > > > >
> > > > > -       if (!vi->big_packets || vi->mergeable_rx_bufs) {
> > > > > -               void *ctx;
> > > > > +       if (rq->xsk.pool) {
> > > > > +               struct sk_buff *skb;
> > > > > +
> > > > > +               while (packets < budget) {
> > > > > +                       buf = virtqueue_get_buf(rq->vq, &len);
> > > > > +                       if (!buf)
> > > > > +                               break;
> > > > >
> > > > > +                       skb = virtnet_receive_xsk_buf(vi, rq, buf, len, xdp_xmit, &stats);
> > > > > +                       if (skb)
> > > > > +                               virtnet_receive_done(vi, rq, skb);
> > > > > +
> > > > > +                       packets++;
> > > > > +               }
> > > >
> > > > If reusing turns out to be hard, I'd rather add new paths in receive_small().
> > >
> > > The exist function is called after virtnet_rq_get_buf(), that will do dma unmap.
> > > But for xsk, the dma unmap is not need. So xsk receive handle should use
> > > virtqueue_get_buf directly.
> >
> > Probably but if it's just virtnet_rq_get_buf() we can simply did:
> >
> > static void *virtnet_rq_get_buf(struct receive_queue *rq, u32 *len, void **ctx)
> > {
> >         void *buf;
> >
> >         buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
> >         if (buf && rq->xsk.pool)
> >                 virtnet_rq_unmap(rq, buf, *len);
> >
> >         return buf;
> > }
>
> Or maybe it would be much more clearer if we did:
>
> static int virtnet_receive()
> {
>
> if (rq->xsk.pool)
>         virtnet_receive_xsk()
> else
>         virtnet_receive_xxx()
> ...
> }

I like this.

Thanks.


>
> Thanks
>
> >
> > Thanks
> >
> > >
> > > Thanks.
> > >
> > > >
> > > > > +       } else if (!vi->big_packets || vi->mergeable_rx_bufs) {
> > > > > +               void *ctx;
> > > > >                 while (packets < budget &&
> > > > >                        (buf = virtnet_rq_get_buf(rq, &len, &ctx))) {
> > > > >                         receive_buf(vi, rq, buf, len, ctx, xdp_xmit, &stats);
> > > > > --
> > > > > 2.32.0.3.g01195cf9f
> > > > >
> > > >
> > > > Thanks
> > > >
> > >
>