linux-kernel - Re: [PATCH net-next 3/3] virtio

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Message-ID: <CACGkMEtjERF72zkLzDn2OKz3OGkJOQ+FCJS3MRscJqakEz9FYA@mail.gmail.com>
Date: Mon, 13 Jan 2025 12:05:51 +0800
From: Jason Wang <jasowang@...hat.com>
To: Joe Damato <jdamato@...tly.com>
Cc: netdev@...r.kernel.org, mkarsten@...terloo.ca, 
	"Michael S. Tsirkin" <mst@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
	Eugenio Pérez <eperezma@...hat.com>, 
	Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	"open list:VIRTIO CORE AND NET DRIVERS" <virtualization@...ts.linux.dev>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 3/3] virtio_net: Map NAPIs to queues

On Sat, Jan 11, 2025 at 4:26 AM Joe Damato <jdamato@...tly.com> wrote:
>
> Use netif_queue_set_napi to map NAPIs to queue IDs so that the mapping
> can be accessed by user apps.
>
> $ ethtool -i ens4 | grep driver
> driver: virtio_net
>
> $ sudo ethtool -L ens4 combined 4
>
> $ ./tools/net/ynl/pyynl/cli.py \
>        --spec Documentation/netlink/specs/netdev.yaml \
>        --dump queue-get --json='{"ifindex": 2}'
> [{'id': 0, 'ifindex': 2, 'napi-id': 8289, 'type': 'rx'},
>  {'id': 1, 'ifindex': 2, 'napi-id': 8290, 'type': 'rx'},
>  {'id': 2, 'ifindex': 2, 'napi-id': 8291, 'type': 'rx'},
>  {'id': 3, 'ifindex': 2, 'napi-id': 8292, 'type': 'rx'},
>  {'id': 0, 'ifindex': 2, 'type': 'tx'},
>  {'id': 1, 'ifindex': 2, 'type': 'tx'},
>  {'id': 2, 'ifindex': 2, 'type': 'tx'},
>  {'id': 3, 'ifindex': 2, 'type': 'tx'}]
>
> Note that virtio_net has TX-only NAPIs which do not have NAPI IDs, so
> the lack of 'napi-id' in the above output is expected.
>
> Signed-off-by: Joe Damato <jdamato@...tly.com>
> ---
>  drivers/net/virtio_net.c | 29 ++++++++++++++++++++++++++---
>  1 file changed, 26 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 4e88d352d3eb..8f0f26cc5a94 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2804,14 +2804,28 @@ static void virtnet_napi_do_enable(struct virtqueue *vq,
>  }
>
>  static void virtnet_napi_enable_lock(struct virtqueue *vq,
> -                                    struct napi_struct *napi)
> +                                    struct napi_struct *napi,
> +                                    bool need_rtnl)
>  {
> +       struct virtnet_info *vi = vq->vdev->priv;
> +       int q = vq2rxq(vq);
> +
>         virtnet_napi_do_enable(vq, napi);
> +
> +       if (q < vi->curr_queue_pairs) {
> +               if (need_rtnl)
> +                       rtnl_lock();

Can we tweak the caller to call rtnl_lock() instead to avoid this trick?

> +
> +               netif_queue_set_napi(vi->dev, q, NETDEV_QUEUE_TYPE_RX, napi);
> +
> +               if (need_rtnl)
> +                       rtnl_unlock();
> +       }
>  }
>
>  static void virtnet_napi_enable(struct virtqueue *vq, struct napi_struct *napi)
>  {
> -       virtnet_napi_enable_lock(vq, napi);
> +       virtnet_napi_enable_lock(vq, napi, false);
>  }
>
>  static void virtnet_napi_tx_enable(struct virtnet_info *vi,
> @@ -2848,9 +2862,13 @@ static void refill_work(struct work_struct *work)
>         for (i = 0; i < vi->curr_queue_pairs; i++) {
>                 struct receive_queue *rq = &vi->rq[i];
>
> +               rtnl_lock();
> +               netif_queue_set_napi(vi->dev, i, NETDEV_QUEUE_TYPE_RX, NULL);
> +               rtnl_unlock();
>                 napi_disable(&rq->napi);

I wonder if it's better to have a helper to do set napi to NULL as
well as napi_disable().

> +
>                 still_empty = !try_fill_recv(vi, rq, GFP_KERNEL);
> -               virtnet_napi_enable_lock(rq->vq, &rq->napi);
> +               virtnet_napi_enable_lock(rq->vq, &rq->napi, true);
>
>                 /* In theory, this can happen: if we don't get any buffers in
>                  * we will *never* try to fill again.
> @@ -3048,6 +3066,7 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
>  static void virtnet_disable_queue_pair(struct virtnet_info *vi, int qp_index)
>  {
>         virtnet_napi_tx_disable(&vi->sq[qp_index].napi);
> +       netif_queue_set_napi(vi->dev, qp_index, NETDEV_QUEUE_TYPE_RX, NULL);
>         napi_disable(&vi->rq[qp_index].napi);
>         xdp_rxq_info_unreg(&vi->rq[qp_index].xdp_rxq);
>  }
> @@ -3317,8 +3336,10 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
>  static void virtnet_rx_pause(struct virtnet_info *vi, struct receive_queue *rq)
>  {
>         bool running = netif_running(vi->dev);
> +       int q = vq2rxq(rq->vq);
>
>         if (running) {
> +               netif_queue_set_napi(vi->dev, q, NETDEV_QUEUE_TYPE_RX, NULL);
>                 napi_disable(&rq->napi);
>                 virtnet_cancel_dim(vi, &rq->dim);
>         }
> @@ -5943,6 +5964,8 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
>         /* Make sure NAPI is not using any XDP TX queues for RX. */
>         if (netif_running(dev)) {
>                 for (i = 0; i < vi->max_queue_pairs; i++) {
> +                       netif_queue_set_napi(vi->dev, i, NETDEV_QUEUE_TYPE_RX,
> +                                            NULL);
>                         napi_disable(&vi->rq[i].napi);
>                         virtnet_napi_tx_disable(&vi->sq[i].napi);
>                 }
> --
> 2.25.1
>

Thanks