Re: [PATCH net-next] virtio-net: switch napi_tx without downing nic

[Zhu Yanjun <yanjun.zhu@linux.dev>]

在 2023/12/20 16:07, Heng Qi 写道:
> virtio-net has two ways to switch napi_tx: one is through the
> module parameter, and the other is through coalescing parameter
> settings (provided that the nic status is down).
> 
> Sometimes we face performance regression caused by napi_tx,
> then we need to switch napi_tx when debugging. However, the
> existing methods are a bit troublesome, such as needing to
> reload the driver or turn off the network card. So try to make
> this update.

What scenario can trigger this? We want to make tests on our device.

Zhu Yanjun

> 
> Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> ---
>   drivers/net/virtio_net.c | 81 ++++++++++++++++++----------------------
>   1 file changed, 37 insertions(+), 44 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 10614e9f7cad..12f8e1f9971c 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3559,16 +3559,37 @@ static int virtnet_coal_params_supported(struct ethtool_coalesce *ec)
>   	return 0;
>   }
>   
> -static int virtnet_should_update_vq_weight(int dev_flags, int weight,
> -					   int vq_weight, bool *should_update)
> +static void virtnet_switch_napi_tx(struct virtnet_info *vi, u32 qstart,
> +				   u32 qend, u32 tx_frames)
>   {
> -	if (weight ^ vq_weight) {
> -		if (dev_flags & IFF_UP)
> -			return -EBUSY;
> -		*should_update = true;
> -	}
> +	struct net_device *dev = vi->dev;
> +	int new_weight, cur_weight;
> +	struct netdev_queue *txq;
> +	struct send_queue *sq;
>   
> -	return 0;
> +	new_weight = tx_frames ? NAPI_POLL_WEIGHT : 0;
> +	for (; qstart < qend; qstart++) {
> +		sq = &vi->sq[qstart];
> +		cur_weight = sq->napi.weight;
> +		if (!(new_weight ^ cur_weight))
> +			continue;
> +
> +		if (!(dev->flags & IFF_UP)) {
> +			sq->napi.weight = new_weight;
> +			continue;
> +		}
> +
> +		if (cur_weight)
> +			virtnet_napi_tx_disable(&sq->napi);
> +
> +		txq = netdev_get_tx_queue(dev, qstart);
> +		__netif_tx_lock_bh(txq);
> +		sq->napi.weight = new_weight;
> +		__netif_tx_unlock_bh(txq);
> +
> +		if (!cur_weight)
> +			virtnet_napi_tx_enable(vi, sq->vq, &sq->napi);
> +	}
>   }
>   
>   static int virtnet_set_coalesce(struct net_device *dev,
> @@ -3577,25 +3598,11 @@ static int virtnet_set_coalesce(struct net_device *dev,
>   				struct netlink_ext_ack *extack)
>   {
>   	struct virtnet_info *vi = netdev_priv(dev);
> -	int ret, queue_number, napi_weight;
> -	bool update_napi = false;
> -
> -	/* Can't change NAPI weight if the link is up */
> -	napi_weight = ec->tx_max_coalesced_frames ? NAPI_POLL_WEIGHT : 0;
> -	for (queue_number = 0; queue_number < vi->max_queue_pairs; queue_number++) {
> -		ret = virtnet_should_update_vq_weight(dev->flags, napi_weight,
> -						      vi->sq[queue_number].napi.weight,
> -						      &update_napi);
> -		if (ret)
> -			return ret;
> -
> -		if (update_napi) {
> -			/* All queues that belong to [queue_number, vi->max_queue_pairs] will be
> -			 * updated for the sake of simplicity, which might not be necessary
> -			 */
> -			break;
> -		}
> -	}
> +	int ret;
> +
> +	/* Param tx_frames can be used to switch napi_tx */
> +	virtnet_switch_napi_tx(vi, 0, vi->max_queue_pairs,
> +			       ec->tx_max_coalesced_frames);
>   
>   	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_NOTF_COAL))
>   		ret = virtnet_send_notf_coal_cmds(vi, ec);
> @@ -3605,11 +3612,6 @@ static int virtnet_set_coalesce(struct net_device *dev,
>   	if (ret)
>   		return ret;
>   
> -	if (update_napi) {
> -		for (; queue_number < vi->max_queue_pairs; queue_number++)
> -			vi->sq[queue_number].napi.weight = napi_weight;
> -	}
> -
>   	return ret;
>   }
>   
> @@ -3641,19 +3643,13 @@ static int virtnet_set_per_queue_coalesce(struct net_device *dev,
>   					  struct ethtool_coalesce *ec)
>   {
>   	struct virtnet_info *vi = netdev_priv(dev);
> -	int ret, napi_weight;
> -	bool update_napi = false;
> +	int ret;
>   
>   	if (queue >= vi->max_queue_pairs)
>   		return -EINVAL;
>   
> -	/* Can't change NAPI weight if the link is up */
> -	napi_weight = ec->tx_max_coalesced_frames ? NAPI_POLL_WEIGHT : 0;
> -	ret = virtnet_should_update_vq_weight(dev->flags, napi_weight,
> -					      vi->sq[queue].napi.weight,
> -					      &update_napi);
> -	if (ret)
> -		return ret;
> +	/* Param tx_frames can be used to switch napi_tx */
> +	virtnet_switch_napi_tx(vi, queue, queue, ec->tx_max_coalesced_frames);
>   
>   	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL))
>   		ret = virtnet_send_notf_coal_vq_cmds(vi, ec, queue);
> @@ -3663,9 +3659,6 @@ static int virtnet_set_per_queue_coalesce(struct net_device *dev,
>   	if (ret)
>   		return ret;
>   
> -	if (update_napi)
> -		vi->sq[queue].napi.weight = napi_weight;
> -
>   	return 0;
>   }
>