[PATCH net-next 0/3] virtio_net: Link queues to NAPIs

[PATCH net-next 0/3] virtio_net: Link queues to NAPIs

[Joe Damato]

Greetings:

Recently [1], Jakub mentioned that there were a few drivers that are not
yet mapping queues to NAPIs.

While I don't have any of the other hardware mentioned, I do happen to
have a virtio_net laying around ;)

I've attempted to link queues to NAPIs, taking care to hold RTNL when it
seemed that the path was not already holding it.

Note: It seems virtio_net uses TX-only NAPIs which do not have NAPI IDs.
As such, I've left the TX NAPIs unset (as opposed to setting them to 0).

See the commit message of patch 3 for example out to see what I mean.

Thanks,
Joe

[1]: https://lore.kernel.org/netdev/20250109084301.2445a3e3@kernel.org/

Joe Damato (3):
  virtio_net: Prepare for NAPI to queue mapping
  virtio_net: Hold RTNL for NAPI to queue mapping
  virtio_net: Map NAPIs to queues

 drivers/net/virtio_net.c | 48 ++++++++++++++++++++++++++++++++++++----
 1 file changed, 44 insertions(+), 4 deletions(-)


base-commit: 7b24f164cf005b9649138ef6de94aaac49c9f3d1
-- 
2.25.1

[PATCH net-next 1/3] virtio_net: Prepare for NAPI to queue mapping

[Joe Damato]

Slight refactor to prepare the code for NAPI to queue mapping. No
functional changes.

Signed-off-by: Joe Damato <jdamato@fastly.com>
---
 drivers/net/virtio_net.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 7646ddd9bef7..cff18c66b54a 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2789,7 +2789,8 @@ static void skb_recv_done(struct virtqueue *rvq)
 	virtqueue_napi_schedule(&rq->napi, rvq);
 }
 
-static void virtnet_napi_enable(struct virtqueue *vq, struct napi_struct *napi)
+static void virtnet_napi_do_enable(struct virtqueue *vq,
+				   struct napi_struct *napi)
 {
 	napi_enable(napi);
 
@@ -2802,6 +2803,11 @@ static void virtnet_napi_enable(struct virtqueue *vq, struct napi_struct *napi)
 	local_bh_enable();
 }
 
+static void virtnet_napi_enable(struct virtqueue *vq, struct napi_struct *napi)
+{
+	virtnet_napi_do_enable(vq, napi);
+}
+
 static void virtnet_napi_tx_enable(struct virtnet_info *vi,
 				   struct virtqueue *vq,
 				   struct napi_struct *napi)
@@ -2817,7 +2823,7 @@ static void virtnet_napi_tx_enable(struct virtnet_info *vi,
 		return;
 	}
 
-	return virtnet_napi_enable(vq, napi);
+	virtnet_napi_do_enable(vq, napi);
 }
 
 static void virtnet_napi_tx_disable(struct napi_struct *napi)
-- 
2.25.1

Re: [PATCH net-next 1/3] virtio_net: Prepare for NAPI to queue mapping

[Gerhard Engleder]

On 10.01.25 21:26, Joe Damato wrote:
> Slight refactor to prepare the code for NAPI to queue mapping. No
> functional changes.
> 
> Signed-off-by: Joe Damato <jdamato@fastly.com>
> ---
>   drivers/net/virtio_net.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 7646ddd9bef7..cff18c66b54a 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2789,7 +2789,8 @@ static void skb_recv_done(struct virtqueue *rvq)
>   	virtqueue_napi_schedule(&rq->napi, rvq);
>   }
>   
> -static void virtnet_napi_enable(struct virtqueue *vq, struct napi_struct *napi)
> +static void virtnet_napi_do_enable(struct virtqueue *vq,
> +				   struct napi_struct *napi)
>   {
>   	napi_enable(napi);
>   
> @@ -2802,6 +2803,11 @@ static void virtnet_napi_enable(struct virtqueue *vq, struct napi_struct *napi)
>   	local_bh_enable();
>   }
>   
> +static void virtnet_napi_enable(struct virtqueue *vq, struct napi_struct *napi)
> +{
> +	virtnet_napi_do_enable(vq, napi);
> +}
> +
>   static void virtnet_napi_tx_enable(struct virtnet_info *vi,
>   				   struct virtqueue *vq,
>   				   struct napi_struct *napi)
> @@ -2817,7 +2823,7 @@ static void virtnet_napi_tx_enable(struct virtnet_info *vi,
>   		return;
>   	}
>   
> -	return virtnet_napi_enable(vq, napi);
> +	virtnet_napi_do_enable(vq, napi);
>   }
>   
>   static void virtnet_napi_tx_disable(struct napi_struct *napi)

Reviewed-by: Gerhard Engleder <gerhard@engleder-embedded.com>

[PATCH net-next 2/3] virtio_net: Hold RTNL for NAPI to queue mapping

[Joe Damato]

Prepare for NAPI to queue mapping by holding RTNL in code paths where
NAPIs will be mapped to queue IDs and RTNL is not currently held.

Signed-off-by: Joe Damato <jdamato@fastly.com>
---
 drivers/net/virtio_net.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index cff18c66b54a..4e88d352d3eb 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2803,11 +2803,17 @@ static void virtnet_napi_do_enable(struct virtqueue *vq,
 	local_bh_enable();
 }
 
-static void virtnet_napi_enable(struct virtqueue *vq, struct napi_struct *napi)
+static void virtnet_napi_enable_lock(struct virtqueue *vq,
+				     struct napi_struct *napi)
 {
 	virtnet_napi_do_enable(vq, napi);
 }
 
+static void virtnet_napi_enable(struct virtqueue *vq, struct napi_struct *napi)
+{
+	virtnet_napi_enable_lock(vq, napi);
+}
+
 static void virtnet_napi_tx_enable(struct virtnet_info *vi,
 				   struct virtqueue *vq,
 				   struct napi_struct *napi)
@@ -2844,7 +2850,7 @@ static void refill_work(struct work_struct *work)
 
 		napi_disable(&rq->napi);
 		still_empty = !try_fill_recv(vi, rq, GFP_KERNEL);
-		virtnet_napi_enable(rq->vq, &rq->napi);
+		virtnet_napi_enable_lock(rq->vq, &rq->napi);
 
 		/* In theory, this can happen: if we don't get any buffers in
 		 * we will *never* try to fill again.
@@ -5621,8 +5627,11 @@ static void virtnet_freeze_down(struct virtio_device *vdev)
 	netif_tx_lock_bh(vi->dev);
 	netif_device_detach(vi->dev);
 	netif_tx_unlock_bh(vi->dev);
-	if (netif_running(vi->dev))
+	if (netif_running(vi->dev)) {
+		rtnl_lock();
 		virtnet_close(vi->dev);
+		rtnl_unlock();
+	}
 }
 
 static int init_vqs(struct virtnet_info *vi);
@@ -5642,7 +5651,9 @@ static int virtnet_restore_up(struct virtio_device *vdev)
 	enable_rx_mode_work(vi);
 
 	if (netif_running(vi->dev)) {
+		rtnl_lock();
 		err = virtnet_open(vi->dev);
+		rtnl_unlock();
 		if (err)
 			return err;
 	}
-- 
2.25.1

Re: [PATCH net-next 2/3] virtio_net: Hold RTNL for NAPI to queue mapping

[Gerhard Engleder]

On 10.01.25 21:26, Joe Damato wrote:
> Prepare for NAPI to queue mapping by holding RTNL in code paths where
> NAPIs will be mapped to queue IDs and RTNL is not currently held.
> 
> Signed-off-by: Joe Damato <jdamato@fastly.com>
> ---
>   drivers/net/virtio_net.c | 17 ++++++++++++++---
>   1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index cff18c66b54a..4e88d352d3eb 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2803,11 +2803,17 @@ static void virtnet_napi_do_enable(struct virtqueue *vq,
>   	local_bh_enable();
>   }
>   
> -static void virtnet_napi_enable(struct virtqueue *vq, struct napi_struct *napi)
> +static void virtnet_napi_enable_lock(struct virtqueue *vq,
> +				     struct napi_struct *napi)
>   {
>   	virtnet_napi_do_enable(vq, napi);
>   }
>   
> +static void virtnet_napi_enable(struct virtqueue *vq, struct napi_struct *napi)
> +{
> +	virtnet_napi_enable_lock(vq, napi);
> +}
> +
>   static void virtnet_napi_tx_enable(struct virtnet_info *vi,
>   				   struct virtqueue *vq,
>   				   struct napi_struct *napi)
> @@ -2844,7 +2850,7 @@ static void refill_work(struct work_struct *work)
>   
>   		napi_disable(&rq->napi);
>   		still_empty = !try_fill_recv(vi, rq, GFP_KERNEL);
> -		virtnet_napi_enable(rq->vq, &rq->napi);
> +		virtnet_napi_enable_lock(rq->vq, &rq->napi);
>   
>   		/* In theory, this can happen: if we don't get any buffers in
>   		 * we will *never* try to fill again.
> @@ -5621,8 +5627,11 @@ static void virtnet_freeze_down(struct virtio_device *vdev)
>   	netif_tx_lock_bh(vi->dev);
>   	netif_device_detach(vi->dev);
>   	netif_tx_unlock_bh(vi->dev);
> -	if (netif_running(vi->dev))
> +	if (netif_running(vi->dev)) {
> +		rtnl_lock();
>   		virtnet_close(vi->dev);
> +		rtnl_unlock();
> +	}
>   }
>   
>   static int init_vqs(struct virtnet_info *vi);
> @@ -5642,7 +5651,9 @@ static int virtnet_restore_up(struct virtio_device *vdev)
>   	enable_rx_mode_work(vi);
>   
>   	if (netif_running(vi->dev)) {
> +		rtnl_lock();
>   		err = virtnet_open(vi->dev);
> +		rtnl_unlock();
>   		if (err)
>   			return err;
>   	}

Reviewed-by: Gerhard Engleder <gerhard@engleder-embedded.com>

[PATCH net-next 3/3] virtio_net: Map NAPIs to queues

[Joe Damato]

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@fastly.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();
+
+		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);
+
 		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

Re: [PATCH net-next 3/3] virtio_net: Map NAPIs to queues

[Gerhard Engleder]

On 10.01.25 21:26, Joe Damato 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@fastly.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();
> +
> +		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);
> +
>   		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);
>   		}

Reviewed-by: Gerhard Engleder <gerhard@engleder-embedded.com>

Re: [PATCH net-next 3/3] virtio_net: Map NAPIs to queues

[Jason Wang]

On Sat, Jan 11, 2025 at 4:26 AM Joe Damato <jdamato@fastly.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@fastly.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

Re: [PATCH net-next 3/3] virtio_net: Map NAPIs to queues

[Joe Damato]

On Mon, Jan 13, 2025 at 12:05:51PM +0800, Jason Wang wrote:
> On Sat, Jan 11, 2025 at 4:26 AM Joe Damato <jdamato@fastly.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@fastly.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?

The major problem is that if the caller calls rtnl_lock() before
calling virtnet_napi_enable_lock, then virtnet_napi_do_enable (and
thus napi_enable) happen under the lock.

Jakub mentioned in a recent change [1] that napi_enable may soon
need to sleep.

Given the above constraints, the only way to avoid the "need_rtnl"
would be to refactor the code much more, placing calls (or wrappers)
to netif_queue_set_napi in many locations.

IMHO: This implementation seemed cleaner than putting calls to
netif_queue_set_napi throughout the driver.

Please let me know how you'd like to proceed on this.

[1]: https://lore.kernel.org/netdev/20250111024742.3680902-1-kuba@kernel.org/

> > +
> > +               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().

There are a couple places where this code is repeated, so I could do
that, but I'd probably employ the same "trick" as above with a flag
for "need_rtnl" in the helper.

I can send a v2 which adds a virtnet_napi_disable_lock and call it
from the 4 sites I see that can use it (virtnet_xdp_set,
virtnet_rx_pause, virtnet_disable_queue_pair, refill_work).

But first.... we need to agree on the flag being passed in to hold
rtnl :)

Please let me know.

Thanks for the review.

Re: [PATCH net-next 3/3] virtio_net: Map NAPIs to queues

[Jakub Kicinski]

On Mon, 13 Jan 2025 09:30:20 -0800 Joe Damato wrote:
> > >  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?  
> 
> The major problem is that if the caller calls rtnl_lock() before
> calling virtnet_napi_enable_lock, then virtnet_napi_do_enable (and
> thus napi_enable) happen under the lock.
> 
> Jakub mentioned in a recent change [1] that napi_enable may soon
> need to sleep.
> 
> Given the above constraints, the only way to avoid the "need_rtnl"
> would be to refactor the code much more, placing calls (or wrappers)
> to netif_queue_set_napi in many locations.
> 
> IMHO: This implementation seemed cleaner than putting calls to
> netif_queue_set_napi throughout the driver.
> 
> Please let me know how you'd like to proceed on this.
> 
> [1]: https://lore.kernel.org/netdev/20250111024742.3680902-1-kuba@kernel.org/

I'm going to make netif_queue_set_napi() take netdev->lock, and remove
the rtnl_lock requirement ~this week. If we need conditional locking
perhaps we're better off waiting?

Re: [PATCH net-next 3/3] virtio_net: Map NAPIs to queues

[Joe Damato]

On Mon, Jan 13, 2025 at 02:04:46PM -0800, Jakub Kicinski wrote:
> On Mon, 13 Jan 2025 09:30:20 -0800 Joe Damato wrote:
> > > >  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?  
> > 
> > The major problem is that if the caller calls rtnl_lock() before
> > calling virtnet_napi_enable_lock, then virtnet_napi_do_enable (and
> > thus napi_enable) happen under the lock.
> > 
> > Jakub mentioned in a recent change [1] that napi_enable may soon
> > need to sleep.
> > 
> > Given the above constraints, the only way to avoid the "need_rtnl"
> > would be to refactor the code much more, placing calls (or wrappers)
> > to netif_queue_set_napi in many locations.
> > 
> > IMHO: This implementation seemed cleaner than putting calls to
> > netif_queue_set_napi throughout the driver.
> > 
> > Please let me know how you'd like to proceed on this.
> > 
> > [1]: https://lore.kernel.org/netdev/20250111024742.3680902-1-kuba@kernel.org/
> 
> I'm going to make netif_queue_set_napi() take netdev->lock, and remove
> the rtnl_lock requirement ~this week. If we need conditional locking
> perhaps we're better off waiting?

That seems reasonable to me and I can wait.

Please CC me on that series so I can take a look and I'll adjust the
v2 of this series to avoid the locking once your series is merged.

Thanks!

Re: [PATCH net-next 3/3] virtio_net: Map NAPIs to queues

[Jakub Kicinski]

On Mon, 13 Jan 2025 14:23:56 -0800 Joe Damato wrote:
> Please CC me on that series so I can take a look and I'll adjust the
> v2 of this series to avoid the locking once your series is merged.

Will do! I'll send the first chunk as soon as Comcast restores 
the internet at my home :|

Re: [PATCH net-next 0/3] virtio_net: Link queues to NAPIs

[Lei Yang]

I tested this series of patches with virtio-net regression tests,
everything works fine.

Tested-by: Lei Yang <leiyang@redhat.com>


On Sat, Jan 11, 2025 at 4:26 AM Joe Damato <jdamato@fastly.com> wrote:
>
> Greetings:
>
> Recently [1], Jakub mentioned that there were a few drivers that are not
> yet mapping queues to NAPIs.
>
> While I don't have any of the other hardware mentioned, I do happen to
> have a virtio_net laying around ;)
>
> I've attempted to link queues to NAPIs, taking care to hold RTNL when it
> seemed that the path was not already holding it.
>
> Note: It seems virtio_net uses TX-only NAPIs which do not have NAPI IDs.
> As such, I've left the TX NAPIs unset (as opposed to setting them to 0).
>
> See the commit message of patch 3 for example out to see what I mean.
>
> Thanks,
> Joe
>
> [1]: https://lore.kernel.org/netdev/20250109084301.2445a3e3@kernel.org/
>
> Joe Damato (3):
>   virtio_net: Prepare for NAPI to queue mapping
>   virtio_net: Hold RTNL for NAPI to queue mapping
>   virtio_net: Map NAPIs to queues
>
>  drivers/net/virtio_net.c | 48 ++++++++++++++++++++++++++++++++++++----
>  1 file changed, 44 insertions(+), 4 deletions(-)
>
>
> base-commit: 7b24f164cf005b9649138ef6de94aaac49c9f3d1
> --
> 2.25.1
>
>