linux-kernel - [PATCH] virtio_net: Eliminate OOO packets during switching

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Message-Id: <20240614220422.42733-1-jain.abhinav177@gmail.com>
Date: Fri, 14 Jun 2024 22:04:22 +0000
From: Abhinav Jain <jain.abhinav177@...il.com>
To: mst@...hat.com,
	jasowang@...hat.com,
	xuanzhuo@...ux.alibaba.com,
	eperezma@...hat.com,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	virtualization@...ts.linux.dev,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: skhan@...uxfoundation.org,
	javier.carrasco.cruz@...il.com,
	jain.abhinav177@...il.com
Subject: [PATCH] virtio_net: Eliminate OOO packets during switching

Disable the network device & turn off carrier before modifying the
number of queue pairs.
Process all the in-flight packets and then turn on carrier, followed
by waking up all the queues on the network device.

Signed-off-by: Abhinav Jain <jain.abhinav177@...il.com>
---
 drivers/net/virtio_net.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 61a57d134544..d0a655a3b4c6 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3447,7 +3447,6 @@ static void virtnet_get_drvinfo(struct net_device *dev,
 
 }
 
-/* TODO: Eliminate OOO packets during switching */
 static int virtnet_set_channels(struct net_device *dev,
 				struct ethtool_channels *channels)
 {
@@ -3471,6 +3470,15 @@ static int virtnet_set_channels(struct net_device *dev,
 	if (vi->rq[0].xdp_prog)
 		return -EINVAL;
 
+	/* Disable network device to prevent packet processing during
+	 * the switch.
+	 */
+	netif_tx_disable(dev);
+	netif_carrier_off(dev);
+
+	/* Make certain that all in-flight packets are processed. */
+	synchronize_net();
+
 	cpus_read_lock();
 	err = virtnet_set_queues(vi, queue_pairs);
 	if (err) {
@@ -3482,7 +3490,12 @@ static int virtnet_set_channels(struct net_device *dev,
 
 	netif_set_real_num_tx_queues(dev, queue_pairs);
 	netif_set_real_num_rx_queues(dev, queue_pairs);
- err:
+
+	/* Restart the network device */
+	netif_carrier_on(dev);
+	netif_tx_wake_all_queues(dev);
+
+err:
 	return err;
 }
 
-- 
2.34.1