Re: [RFC net-next v3 4/4] virtio_net: Use persistent NAPI config

[Gerhard Engleder <gerhard@engleder-embedded.com>]

On 21.01.25 20:10, Joe Damato wrote:
> Use persistent NAPI config so that NAPI IDs are not renumbered as queue
> counts change.
> 
> $ sudo ethtool -l ens4  | tail -5 | egrep -i '(current|combined)'
> Current hardware settings:
> 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': 8193, 'type': 'rx'},
>   {'id': 1, 'ifindex': 2, 'napi-id': 8194, 'type': 'rx'},
>   {'id': 2, 'ifindex': 2, 'napi-id': 8195, 'type': 'rx'},
>   {'id': 3, 'ifindex': 2, 'napi-id': 8196, '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'}]
> 
> Now adjust the queue count, note that the NAPI IDs are not renumbered:
> 
> $ sudo ethtool -L ens4 combined 1
> $ ./tools/net/ynl/pyynl/cli.py \
>      --spec Documentation/netlink/specs/netdev.yaml \
>      --dump queue-get --json='{"ifindex": 2}'
> [{'id': 0, 'ifindex': 2, 'napi-id': 8193, 'type': 'rx'},
>   {'id': 0, 'ifindex': 2, 'type': 'tx'}]
> 
> $ sudo ethtool -L ens4 combined 8
> $ ./tools/net/ynl/pyynl/cli.py \
>      --spec Documentation/netlink/specs/netdev.yaml \
>      --dump queue-get --json='{"ifindex": 2}'
> [{'id': 0, 'ifindex': 2, 'napi-id': 8193, 'type': 'rx'},
>   {'id': 1, 'ifindex': 2, 'napi-id': 8194, 'type': 'rx'},
>   {'id': 2, 'ifindex': 2, 'napi-id': 8195, 'type': 'rx'},
>   {'id': 3, 'ifindex': 2, 'napi-id': 8196, 'type': 'rx'},
>   {'id': 4, 'ifindex': 2, 'napi-id': 8197, 'type': 'rx'},
>   {'id': 5, 'ifindex': 2, 'napi-id': 8198, 'type': 'rx'},
>   {'id': 6, 'ifindex': 2, 'napi-id': 8199, 'type': 'rx'},
>   {'id': 7, 'ifindex': 2, 'napi-id': 8200, 'type': 'rx'},
>   [...]
> 
> Signed-off-by: Joe Damato <jdamato@fastly.com>
> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> ---
>   rfcv3:
>     - Added Xuan Zhuo's Reviewed-by tag. No functional changes.
> 
>   v2:
>     - Eliminate RTNL code paths using the API Jakub introduced in patch 1
>       of this v2.
>     - Added virtnet_napi_disable to reduce code duplication as
>       suggested by Jason Wang.
> 
>   drivers/net/virtio_net.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index c120cb2106c0..e0752a856adf 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -6411,8 +6411,9 @@ static int virtnet_alloc_queues(struct virtnet_info *vi)
>   	INIT_DELAYED_WORK(&vi->refill, refill_work);
>   	for (i = 0; i < vi->max_queue_pairs; i++) {
>   		vi->rq[i].pages = NULL;
> -		netif_napi_add_weight(vi->dev, &vi->rq[i].napi, virtnet_poll,
> -				      napi_weight);
> +		netif_napi_add_config(vi->dev, &vi->rq[i].napi, virtnet_poll,
> +				      i);
> +		vi->rq[i].napi.weight = napi_weight;
>   		netif_napi_add_tx_weight(vi->dev, &vi->sq[i].napi,
>   					 virtnet_poll_tx,
>   					 napi_tx ? napi_weight : 0);

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