netdev - [PATCH RFC v2 4/5] veth: create by default nr_possible

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Message-Id: <4e1de423e38765b7d1918450daa009b74db4ebe9.1626449533.git.pabeni@redhat.com>
Date:   Fri, 16 Jul 2021 17:34:22 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Shuah Khan <shuah@...nel.org>, toke@...hat.com
Subject: [PATCH RFC v2 4/5] veth: create by default nr_possible_cpus queues

This allows easier XDP usage. The number of default active
queues is not changed: 1 RX and 1 TX so that this does
not introduce overhead on the datapath for queue selection.

v1 -> v2:
 - drop the module parameter, force default to nr_possible_cpus - Toke

Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
note: I think here a kernel module parameter to make the default
num_{r,t}x_queues configurable could be worthy...
---
 drivers/net/veth.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index ae869c097587..381670c08ba7 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -1609,6 +1609,23 @@ static void veth_disable_gro(struct net_device *dev)
 	netdev_update_features(dev);
 }
 
+static int veth_init_queues(struct net_device *dev, struct nlattr *tb[])
+{
+	int err;
+
+	if (!tb[IFLA_NUM_TX_QUEUES] && dev->num_tx_queues > 1) {
+		err = netif_set_real_num_tx_queues(dev, 1);
+		if (err)
+			return err;
+	}
+	if (!tb[IFLA_NUM_RX_QUEUES] && dev->num_rx_queues > 1) {
+		err = netif_set_real_num_rx_queues(dev, 1);
+		if (err)
+			return err;
+	}
+	return 0;
+}
+
 static int veth_newlink(struct net *src_net, struct net_device *dev,
 			struct nlattr *tb[], struct nlattr *data[],
 			struct netlink_ext_ack *extack)
@@ -1718,13 +1735,21 @@ static int veth_newlink(struct net *src_net, struct net_device *dev,
 
 	priv = netdev_priv(dev);
 	rcu_assign_pointer(priv->peer, peer);
+	err = veth_init_queues(dev, tb);
+	if (err)
+		goto err_queues;
 
 	priv = netdev_priv(peer);
 	rcu_assign_pointer(priv->peer, dev);
+	err = veth_init_queues(peer, tb);
+	if (err)
+		goto err_queues;
 
 	veth_disable_gro(dev);
 	return 0;
 
+err_queues:
+	unregister_netdevice(dev);
 err_register_dev:
 	/* nothing to do */
 err_configure_peer:
@@ -1770,6 +1795,16 @@ static struct net *veth_get_link_net(const struct net_device *dev)
 	return peer ? dev_net(peer) : dev_net(dev);
 }
 
+static unsigned int veth_get_num_queues(void)
+{
+	/* enforce the same queue limit as rtnl_create_link */
+	int queues = num_possible_cpus();
+
+	if (queues > 4096)
+		queues = 4096;
+	return queues;
+}
+
 static struct rtnl_link_ops veth_link_ops = {
 	.kind		= DRV_NAME,
 	.priv_size	= sizeof(struct veth_priv),
@@ -1780,6 +1815,8 @@ static struct rtnl_link_ops veth_link_ops = {
 	.policy		= veth_policy,
 	.maxtype	= VETH_INFO_MAX,
 	.get_link_net	= veth_get_link_net,
+	.get_num_tx_queues	= veth_get_num_queues,
+	.get_num_rx_queues	= veth_get_num_queues,
 };
 
 /*
-- 
2.26.3