Re: [PATCH v5 17/22] virtio_net: support rx/tx queue reset

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On Mon, Feb 14, 2022 at 4:14 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
>
> This patch implements the reset function of the rx, tx queues.
>
> Based on this function, it is possible to modify the ring num of the
> queue. And quickly recycle the buffer in the queue.
>
> In the process of the queue disable, in theory, as long as virtio
> supports queue reset, there will be no exceptions.
>
> However, in the process of the queue enable, there may be exceptions due to
> memory allocation.  In this case, vq is not available, but we still have
> to execute napi_enable(). Because napi_disable is similar to a lock,
> napi_enable must be called after calling napi_disable.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> ---
>  drivers/net/virtio_net.c | 123 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 123 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 9a1445236e23..a4ffd7cdf623 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -251,6 +251,11 @@ struct padded_vnet_hdr {
>         char padding[4];
>  };
>
> +static void virtnet_sq_free_unused_bufs(struct virtnet_info *vi,
> +                                       struct send_queue *sq);
> +static void virtnet_rq_free_unused_bufs(struct virtnet_info *vi,
> +                                       struct receive_queue *rq);
> +
>  static bool is_xdp_frame(void *ptr)
>  {
>         return (unsigned long)ptr & VIRTIO_XDP_FLAG;
> @@ -1369,6 +1374,9 @@ static void virtnet_napi_enable(struct virtqueue *vq, struct napi_struct *napi)
>  {
>         napi_enable(napi);
>
> +       if (vq->reset)
> +               return;
> +
>         /* If all buffers were filled by other side before we napi_enabled, we
>          * won't get another interrupt, so process any outstanding packets now.
>          * Call local_bh_enable after to trigger softIRQ processing.
> @@ -1413,6 +1421,10 @@ static void refill_work(struct work_struct *work)
>                 struct receive_queue *rq = &vi->rq[i];
>
>                 napi_disable(&rq->napi);
> +               if (rq->vq->reset) {
> +                       virtnet_napi_enable(rq->vq, &rq->napi);
> +                       continue;
> +               }
>                 still_empty = !try_fill_recv(vi, rq, GFP_KERNEL);
>                 virtnet_napi_enable(rq->vq, &rq->napi);
>
> @@ -1523,6 +1535,9 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
>         if (!sq->napi.weight || is_xdp_raw_buffer_queue(vi, index))
>                 return;
>
> +       if (sq->vq->reset)
> +               return;
> +
>         if (__netif_tx_trylock(txq)) {
>                 do {
>                         virtqueue_disable_cb(sq->vq);
> @@ -1769,6 +1784,114 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
>         return NETDEV_TX_OK;
>  }
>
> +static int virtnet_rx_vq_disable(struct virtnet_info *vi,
> +                                struct receive_queue *rq)
> +{
> +       int err;
> +
> +       napi_disable(&rq->napi);
> +
> +       err = virtio_reset_vq(rq->vq);
> +       if (err)
> +               goto err;
> +
> +       virtnet_rq_free_unused_bufs(vi, rq);
> +
> +       vring_release_virtqueue(rq->vq);
> +
> +       return 0;
> +
> +err:
> +       virtnet_napi_enable(rq->vq, &rq->napi);
> +       return err;
> +}
> +
> +static int virtnet_tx_vq_disable(struct virtnet_info *vi,
> +                                struct send_queue *sq)
> +{
> +       struct netdev_queue *txq;
> +       int err, qindex;
> +
> +       qindex = sq - vi->sq;
> +
> +       txq = netdev_get_tx_queue(vi->dev, qindex);
> +       __netif_tx_lock_bh(txq);
> +
> +       netif_stop_subqueue(vi->dev, qindex);
> +       virtnet_napi_tx_disable(&sq->napi);
> +
> +       err = virtio_reset_vq(sq->vq);
> +       if (err) {
> +               virtnet_napi_tx_enable(vi, sq->vq, &sq->napi);
> +               netif_start_subqueue(vi->dev, qindex);
> +
> +               __netif_tx_unlock_bh(txq);
> +               return err;
> +       }
> +       __netif_tx_unlock_bh(txq);
> +
> +       virtnet_sq_free_unused_bufs(vi, sq);
> +
> +       vring_release_virtqueue(sq->vq);
> +
> +       return 0;
> +}
> +
> +static int virtnet_tx_vq_enable(struct virtnet_info *vi, struct send_queue *sq)
> +{
> +       int err;
> +
> +       err = virtio_enable_resetq(sq->vq);
> +       if (!err)
> +               netif_start_subqueue(vi->dev, sq - vi->sq);
> +
> +       virtnet_napi_tx_enable(vi, sq->vq, &sq->napi);
> +
> +       return err;
> +}
> +
> +static int virtnet_rx_vq_enable(struct virtnet_info *vi,
> +                               struct receive_queue *rq)
> +{
> +       int err;

So the API should be design in a consistent way.

In rx_vq_disable() we do:

reset()
detach_unused_bufs()
vring_release_virtqueue()

here it's better to exactly the reverse

vring_attach_virtqueue() // this is the helper I guess in patch 5,
reverse of the vring_release_virtqueue()
try_refill_recv() // reverse of the detach_unused_bufs()
enable_reset() // reverse of the reset

So did for the tx (no need for refill in that case).

> +
> +       err = virtio_enable_resetq(rq->vq);
> +
> +       virtnet_napi_enable(rq->vq, &rq->napi);
> +
> +       return err;
> +}
> +
> +static int virtnet_rx_vq_reset(struct virtnet_info *vi, int i)
> +{
> +       int err;
> +
> +       err = virtnet_rx_vq_disable(vi, vi->rq + i);
> +       if (err)
> +               return err;
> +
> +       err = virtnet_rx_vq_enable(vi, vi->rq + i);
> +       if (err)
> +               netdev_err(vi->dev,
> +                          "enable rx reset vq fail: rx queue index: %d err: %d\n", i, err);
> +       return err;
> +}
> +
> +static int virtnet_tx_vq_reset(struct virtnet_info *vi, int i)
> +{
> +       int err;
> +
> +       err = virtnet_tx_vq_disable(vi, vi->sq + i);
> +       if (err)
> +               return err;
> +
> +       err = virtnet_tx_vq_enable(vi, vi->sq + i);
> +       if (err)
> +               netdev_err(vi->dev,
> +                          "enable tx reset vq fail: tx queue index: %d err: %d\n", i, err);
> +       return err;
> +}
> +
>  /*
>   * Send command via the control virtqueue and check status.  Commands
>   * supported by the hypervisor, as indicated by feature bits, should
> --
> 2.31.0
>




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