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

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Date: Mon, 17 Jun 2024 09:51:30 +0800
From: Jason Wang <jasowang@...hat.com>
To: Abhinav Jain <jain.abhinav177@...il.com>
Cc: mst@...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, skhan@...uxfoundation.org, 
	javier.carrasco.cruz@...il.com
Subject: Re: [PATCH] virtio_net: Eliminate OOO packets during switching

On Sat, Jun 15, 2024 at 6:05 AM Abhinav Jain <jain.abhinav177@...il.com> wrote:
>
> 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);

Any reason we don't need to synchronize with NAPI here?

Thanks

> +
> +       /* 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
>