Message-ID: <1726130924.279801-7-xuanzhuo@linux.alibaba.com>
Date: Thu, 12 Sep 2024 16:48:44 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Jason Wang <jasowang@...hat.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 10/13] virtio_net: xsk: tx: support xmit xsk buffer

On Wed, 11 Sep 2024 12:31:32 +0800, Jason Wang <jasowang@...hat.com> wrote:
> On Tue, Aug 20, 2024 at 3:33 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> >
> > The driver's tx napi is very important for XSK. It is responsible for
> > obtaining data from the XSK queue and sending it out.
> >
> > At the beginning, we need to trigger tx napi.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > ---
> >  drivers/net/virtio_net.c | 127 ++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 125 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 221681926d23..3743694d3c3b 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -516,10 +516,13 @@ enum virtnet_xmit_type {
> >         VIRTNET_XMIT_TYPE_SKB,
> >         VIRTNET_XMIT_TYPE_ORPHAN,
> >         VIRTNET_XMIT_TYPE_XDP,
> > +       VIRTNET_XMIT_TYPE_XSK,
> >  };
> >
> >  #define VIRTNET_XMIT_TYPE_MASK (VIRTNET_XMIT_TYPE_SKB | VIRTNET_XMIT_TYPE_ORPHAN \
> > -                               | VIRTNET_XMIT_TYPE_XDP)
> > +                               | VIRTNET_XMIT_TYPE_XDP | VIRTNET_XMIT_TYPE_XSK)
> > +
> > +#define VIRTIO_XSK_FLAG_OFFSET 4
> >
> >  static enum virtnet_xmit_type virtnet_xmit_ptr_strip(void **ptr)
> >  {
> > @@ -543,6 +546,11 @@ static int virtnet_add_outbuf(struct send_queue *sq, int num, void *data,
> >                                     GFP_ATOMIC);
> >  }
> >
> > +static u32 virtnet_ptr_to_xsk(void *ptr)
> > +{
> > +       return ((unsigned long)ptr) >> VIRTIO_XSK_FLAG_OFFSET;
> > +}
> > +
>
> This needs a better name, otherwise readers might be confused.
>
> E.g something like virtnet_ptr_to_xsk_buff_len()?
>
> >  static void sg_fill_dma(struct scatterlist *sg, dma_addr_t addr, u32 len)
> >  {
> >         sg_assign_page(sg, NULL);
> > @@ -584,6 +592,10 @@ static void __free_old_xmit(struct send_queue *sq, struct netdev_queue *txq,
> >                         stats->bytes += xdp_get_frame_len(frame);
> >                         xdp_return_frame(frame);
> >                         break;
> > +
> > +               case VIRTNET_XMIT_TYPE_XSK:
> > +                       stats->bytes += virtnet_ptr_to_xsk(ptr);
> > +                       break;
>
> Do we miss xsk_tx_completed() here?
>
> >                 }
> >         }
> >         netdev_tx_completed_queue(txq, stats->napi_packets, stats->napi_bytes);
> > @@ -1393,6 +1405,97 @@ static int virtnet_xsk_wakeup(struct net_device *dev, u32 qid, u32 flag)
> >         return 0;
> >  }
> >
> > +static void *virtnet_xsk_to_ptr(u32 len)
> > +{
> > +       unsigned long p;
> > +
> > +       p = len << VIRTIO_XSK_FLAG_OFFSET;
> > +
> > +       return virtnet_xmit_ptr_mix((void *)p, VIRTNET_XMIT_TYPE_XSK);
> > +}
> > +
> > +static int virtnet_xsk_xmit_one(struct send_queue *sq,
> > +                               struct xsk_buff_pool *pool,
> > +                               struct xdp_desc *desc)
> > +{
> > +       struct virtnet_info *vi;
> > +       dma_addr_t addr;
> > +
> > +       vi = sq->vq->vdev->priv;
> > +
> > +       addr = xsk_buff_raw_get_dma(pool, desc->addr);
> > +       xsk_buff_raw_dma_sync_for_device(pool, addr, desc->len);
> > +
> > +       sg_init_table(sq->sg, 2);
> > +
> > +       sg_fill_dma(sq->sg, sq->xsk_hdr_dma_addr, vi->hdr_len);
> > +       sg_fill_dma(sq->sg + 1, addr, desc->len);
> > +
> > +       return virtqueue_add_outbuf(sq->vq, sq->sg, 2,
> > +                                   virtnet_xsk_to_ptr(desc->len), GFP_ATOMIC);
> > +}
> > +
> > +static int virtnet_xsk_xmit_batch(struct send_queue *sq,
> > +                                 struct xsk_buff_pool *pool,
> > +                                 unsigned int budget,
> > +                                 u64 *kicks)
> > +{
> > +       struct xdp_desc *descs = pool->tx_descs;
> > +       bool kick = false;
> > +       u32 nb_pkts, i;
> > +       int err;
> > +
> > +       budget = min_t(u32, budget, sq->vq->num_free);
> > +
> > +       nb_pkts = xsk_tx_peek_release_desc_batch(pool, budget);
> > +       if (!nb_pkts)
> > +               return 0;
> > +
> > +       for (i = 0; i < nb_pkts; i++) {
> > +               err = virtnet_xsk_xmit_one(sq, pool, &descs[i]);
> > +               if (unlikely(err)) {
> > +                       xsk_tx_completed(sq->xsk_pool, nb_pkts - i);
>
> Should we kick in this condition?
>
> > +                       break;
> > +               }
> > +
> > +               kick = true;
> > +       }
> > +
> > +       if (kick && virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq))
>
> Can we simply use virtqueue_kick() here?
>
> > +               (*kicks)++;
> > +
> > +       return i;
> > +}
> > +
> > +static bool virtnet_xsk_xmit(struct send_queue *sq, struct xsk_buff_pool *pool,
> > +                            int budget)
> > +{
> > +       struct virtnet_info *vi = sq->vq->vdev->priv;
> > +       struct virtnet_sq_free_stats stats = {};
> > +       struct net_device *dev = vi->dev;
> > +       u64 kicks = 0;
> > +       int sent;
> > +
> > +       __free_old_xmit(sq, netdev_get_tx_queue(dev, sq - vi->sq), true, &stats);
>
> I haven't checked in depth, but I wonder if we have some side effects
> when using non NAPI tx mode:
>
>         if (napi->weight)
>                 virtqueue_napi_schedule(napi, vq);
>         else
>                 /* We were probably waiting for more output buffers. */
>                 netif_wake_subqueue(vi->dev, vq2txq(vq));
>
> Does this mean xsk will suffer the same issue like when there's no xsk
> xmit request, we could end up with no way to reclaim xmitted xsk
> buffers? (Or should we disallow AF_XDP to be used for non TX-NAPI
> mode?)

Disallow AF_XDP to be used for non TX-NAPI mode.

The last patch #9 does this.

#9 [PATCH net-next 09/13] virtio_net: xsk: prevent disable tx napi

Thanks.
>
> > +
> > +       sent = virtnet_xsk_xmit_batch(sq, pool, budget, &kicks);
> > +
> > +       if (!is_xdp_raw_buffer_queue(vi, sq - vi->sq))
> > +               check_sq_full_and_disable(vi, vi->dev, sq);
> > +
> > +       u64_stats_update_begin(&sq->stats.syncp);
> > +       u64_stats_add(&sq->stats.packets, stats.packets);
> > +       u64_stats_add(&sq->stats.bytes,   stats.bytes);
> > +       u64_stats_add(&sq->stats.kicks,   kicks);
> > +       u64_stats_add(&sq->stats.xdp_tx,  sent);
> > +       u64_stats_update_end(&sq->stats.syncp);
> > +
> > +       if (xsk_uses_need_wakeup(pool))
> > +               xsk_set_tx_need_wakeup(pool);
> > +
> > +       return sent == budget;
> > +}
> > +
> >  static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
> >                                    struct send_queue *sq,
> >                                    struct xdp_frame *xdpf)
> > @@ -2949,6 +3052,7 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
> >         struct virtnet_info *vi = sq->vq->vdev->priv;
> >         unsigned int index = vq2txq(sq->vq);
> >         struct netdev_queue *txq;
> > +       bool xsk_busy = false;
> >         int opaque;
> >         bool done;
> >
> > @@ -2961,7 +3065,11 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
> >         txq = netdev_get_tx_queue(vi->dev, index);
> >         __netif_tx_lock(txq, raw_smp_processor_id());
> >         virtqueue_disable_cb(sq->vq);
> > -       free_old_xmit(sq, txq, !!budget);
> > +
> > +       if (sq->xsk_pool)
> > +               xsk_busy = virtnet_xsk_xmit(sq, sq->xsk_pool, budget);
> > +       else
> > +               free_old_xmit(sq, txq, !!budget);
> >
> >         if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS) {
> >                 if (netif_tx_queue_stopped(txq)) {
> > @@ -2972,6 +3080,11 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
> >                 netif_tx_wake_queue(txq);
> >         }
> >
> > +       if (xsk_busy) {
> > +               __netif_tx_unlock(txq);
> > +               return budget;
> > +       }
> > +
> >         opaque = virtqueue_enable_cb_prepare(sq->vq);
> >
> >         done = napi_complete_done(napi, 0);
> > @@ -5974,6 +6087,12 @@ static void free_receive_page_frags(struct virtnet_info *vi)
> >
> >  static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf)
> >  {
> > +       struct virtnet_info *vi = vq->vdev->priv;
> > +       struct send_queue *sq;
> > +       int i = vq2rxq(vq);
> > +
> > +       sq = &vi->sq[i];
> > +
> >         switch (virtnet_xmit_ptr_strip(&buf)) {
> >         case VIRTNET_XMIT_TYPE_SKB:
> >         case VIRTNET_XMIT_TYPE_ORPHAN:
> > @@ -5983,6 +6102,10 @@ static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf)
> >         case VIRTNET_XMIT_TYPE_XDP:
> >                 xdp_return_frame(buf);
> >                 break;
> > +
> > +       case VIRTNET_XMIT_TYPE_XSK:
> > +               xsk_tx_completed(sq->xsk_pool, 1);
> > +               break;
> >         }
> >  }
> >
> > --
> > 2.32.0.3.g01195cf9f
> >
>
> Thanks
>

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