On Fri, Jun 14, 2024 at 10:04:22PM +0000, Abhinav Jain 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.
Did you test that there's a workload with OOO and
this patch actually prevents that?
>
> Signed-off-by: Abhinav Jain <jain.abhinav177@xxxxxxxxx>
> ---
> 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);
Won't turning off carrier cause a lot of damage such as
changing IP and so on?
> +
> + /* Make certain that all in-flight packets are processed. */
> + synchronize_net();
> +
The comment seems to say what the code does not do.
Also, doing this under rtnl is a heavy weight operation.
> 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;
> }
>
Given the result is, presumably, improved performance with less
packet loss due to OOO, I'd like to see some actual testing results,
hopefully also measuring the effect on CPU load.
> --
> 2.34.1
