Subject: Re: [PATCH net-next V3 3/4] virtio_net: support per queue interrupt coalesce command

From: "Michael S. Tsirkin" <[email-masked]>
Date: Mon, 24 Jul 2023 03:32:50 -0400

On Mon, Jul 24, 2023 at 06:40:47AM +0300, Gavin Li wrote:
> Add interrupt_coalesce config in send_queue and receive_queue to cache user
> config.
> 
> Send per virtqueue interrupt moderation config to underline device in order
> to have more efficient interrupt moderation and cpu utilization of guest
> VM.
> 
> Signed-off-by: Gavin Li <[email-masked]>
> Reviewed-by: Dragos Tatulea <[email-masked]>
> Reviewed-by: Jiri Pirko <[email-masked]>
> Acked-by: Michael S. Tsirkin <[email-masked]>
> ---
>  drivers/net/virtio_net.c        | 120 ++++++++++++++++++++++++++++----
>  include/uapi/linux/virtio_net.h |  14 ++++
>  2 files changed, 122 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 802ed21453f5..0c3ee1e26ece 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -144,6 +144,8 @@ struct send_queue {
>  
>  	struct virtnet_sq_stats stats;
>  
> +	struct virtnet_interrupt_coalesce intr_coal;
> +
>  	struct napi_struct napi;
>  
>  	/* Record whether sq is in reset state. */
> @@ -161,6 +163,8 @@ struct receive_queue {
>  
>  	struct virtnet_rq_stats stats;
>  
> +	struct virtnet_interrupt_coalesce intr_coal;
> +
>  	/* Chain pages by the private ptr. */
>  	struct page *pages;
>  
> @@ -212,6 +216,7 @@ struct control_buf {
>  	struct virtio_net_ctrl_rss rss;
>  	struct virtio_net_ctrl_coal_tx coal_tx;
>  	struct virtio_net_ctrl_coal_rx coal_rx;
> +	struct virtio_net_ctrl_coal_vq coal_vq;
>  };
>  
>  struct virtnet_info {
> @@ -3078,6 +3083,55 @@ static int virtnet_send_notf_coal_cmds(struct virtnet_info *vi,
>  	return 0;
>  }
>  
> +static int virtnet_send_ctrl_coal_vq_cmd(struct virtnet_info *vi,
> +					 u16 vqn, u32 max_usecs, u32 max_packets)
> +{
> +	struct scatterlist sgs;
> +
> +	vi->ctrl->coal_vq.vqn = cpu_to_le16(vqn);
> +	vi->ctrl->coal_vq.coal.max_usecs = cpu_to_le32(max_usecs);
> +	vi->ctrl->coal_vq.coal.max_packets = cpu_to_le32(max_packets);
> +	sg_init_one(&sgs, &vi->ctrl->coal_vq, sizeof(vi->ctrl->coal_vq));
> +
> +	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_NOTF_COAL,
> +				  VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET,
> +				  &sgs))
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
> +static int virtnet_send_notf_coal_vq_cmds(struct virtnet_info *vi,
> +					  struct ethtool_coalesce *ec,
> +					  u16 queue)
> +{
> +	int err;
> +
> +	if (ec->rx_coalesce_usecs || ec->rx_max_coalesced_frames) {
> +		err = virtnet_send_ctrl_coal_vq_cmd(vi, rxq2vq(queue),
> +						    ec->rx_coalesce_usecs,
> +						    ec->rx_max_coalesced_frames);
> +		if (err)
> +			return err;
> +		/* Save parameters */
> +		vi->rq[queue].intr_coal.max_usecs = ec->rx_coalesce_usecs;
> +		vi->rq[queue].intr_coal.max_packets = ec->rx_max_coalesced_frames;
> +	}
> +
> +	if (ec->tx_coalesce_usecs || ec->tx_max_coalesced_frames) {
> +		err = virtnet_send_ctrl_coal_vq_cmd(vi, txq2vq(queue),
> +						    ec->tx_coalesce_usecs,
> +						    ec->tx_max_coalesced_frames);
> +		if (err)
> +			return err;
> +		/* Save parameters */
> +		vi->sq[queue].intr_coal.max_usecs = ec->tx_coalesce_usecs;
> +		vi->sq[queue].intr_coal.max_packets = ec->tx_max_coalesced_frames;
> +	}
> +
> +	return 0;
> +}
> +
>  static int virtnet_coal_params_supported(struct ethtool_coalesce *ec)
>  {
>  	/* usecs coalescing is supported only if VIRTIO_NET_F_NOTF_COAL
> @@ -3094,23 +3148,39 @@ static int virtnet_coal_params_supported(struct ethtool_coalesce *ec)
>  }
>  
>  static int virtnet_set_coalesce_one(struct net_device *dev,
> -				    struct ethtool_coalesce *ec)
> +				    struct ethtool_coalesce *ec,
> +				    bool per_queue,
> +				    u32 queue)
>  {
>  	struct virtnet_info *vi = netdev_priv(dev);
> -	int ret, i, napi_weight;
> +	int queue_count = per_queue ? 1 : vi->max_queue_pairs;
> +	int queue_number = per_queue ? queue : 0;

Actually can't we refactor this? This whole function is littered
with if/else branches. just code it separately - the only
common part is:

        napi_weight = ec->tx_max_coalesced_frames ? NAPI_POLL_WEIGHT : 0;
        if (napi_weight ^ vi->sq[0].napi.weight) {
                if (dev->flags & IFF_UP)
                        return -EBUSY;
                else
                        update_napi = true;
        }

so just move this to a helper and have two functions - global and
per queue.

>  	bool update_napi = false;
> +	int ret, i, napi_weight;
> +
> +	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;
> -	if (napi_weight ^ vi->sq[0].napi.weight) {
> -		if (dev->flags & IFF_UP)
> -			return -EBUSY;
> -		else
> +	for (i = queue_number; i < queue_count; i++) {
> +		if (napi_weight ^ vi->sq[i].napi.weight) {
> +			if (dev->flags & IFF_UP)
> +				return -EBUSY;
> +
>  			update_napi = true;
> +			/* All queues that belong to [queue_number, queue_count] will be
> +			 * updated for the sake of simplicity, which might not be necessary
> +			 */
> +			queue_number = i;
> +			break;
> +		}
>  	}
>  
> -	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_NOTF_COAL))
> +	if (!per_queue && virtio_has_feature(vi->vdev, VIRTIO_NET_F_NOTF_COAL))
>  		ret = virtnet_send_notf_coal_cmds(vi, ec);
> +	else if (per_queue && virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL))
> +		ret = virtnet_send_notf_coal_vq_cmds(vi, ec, queue);
>  	else
>  		ret = virtnet_coal_params_supported(ec);
>  
> @@ -3118,7 +3188,7 @@ static int virtnet_set_coalesce_one(struct net_device *dev,
>  		return ret;
>  
>  	if (update_napi) {
> -		for (i = 0; i < vi->max_queue_pairs; i++)
> +		for (i = queue_number; i < queue_count; i++)
>  			vi->sq[i].napi.weight = napi_weight;
>  	}
>  
> @@ -3130,19 +3200,29 @@ static int virtnet_set_coalesce(struct net_device *dev,
>  				struct kernel_ethtool_coalesce *kernel_coal,
>  				struct netlink_ext_ack *extack)
>  {
> -	return virtnet_set_coalesce_one(dev, ec);
> +	return virtnet_set_coalesce_one(dev, ec, false, 0);
>  }
>  
>  static int virtnet_get_coalesce_one(struct net_device *dev,
> -				    struct ethtool_coalesce *ec)
> +				    struct ethtool_coalesce *ec,
> +				    bool per_queue,
> +				    u32 queue)
>  {
>  	struct virtnet_info *vi = netdev_priv(dev);
>  
> -	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_NOTF_COAL)) {
> +	if (queue >= vi->max_queue_pairs)
> +		return -EINVAL;
> +
> +	if (!per_queue && virtio_has_feature(vi->vdev, VIRTIO_NET_F_NOTF_COAL)) {
>  		ec->rx_coalesce_usecs = vi->intr_coal_rx.max_usecs;
>  		ec->tx_coalesce_usecs = vi->intr_coal_tx.max_usecs;
>  		ec->tx_max_coalesced_frames = vi->intr_coal_tx.max_packets;
>  		ec->rx_max_coalesced_frames = vi->intr_coal_rx.max_packets;
> +	} else if (per_queue && virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL)) {
> +		ec->rx_coalesce_usecs = vi->rq[queue].intr_coal.max_usecs;
> +		ec->tx_coalesce_usecs = vi->sq[queue].intr_coal.max_usecs;
> +		ec->tx_max_coalesced_frames = vi->sq[queue].intr_coal.max_packets;
> +		ec->rx_max_coalesced_frames = vi->rq[queue].intr_coal.max_packets;
>  	} else {
>  		ec->rx_max_coalesced_frames = 1;
>  
> @@ -3158,7 +3238,21 @@ static int virtnet_get_coalesce(struct net_device *dev,
>  				struct kernel_ethtool_coalesce *kernel_coal,
>  				struct netlink_ext_ack *extack)
>  {
> -	return virtnet_get_coalesce_one(dev, ec);
> +	return virtnet_get_coalesce_one(dev, ec, false, 0);
> +}
> +
> +static int virtnet_set_per_queue_coalesce(struct net_device *dev,
> +					  u32 queue,
> +					  struct ethtool_coalesce *ec)
> +{
> +	return virtnet_set_coalesce_one(dev, ec, true, queue);
> +}
> +
> +static int virtnet_get_per_queue_coalesce(struct net_device *dev,
> +					  u32 queue,
> +					  struct ethtool_coalesce *ec)
> +{
> +	return virtnet_get_coalesce_one(dev, ec, true, queue);
>  }
>  
>  static void virtnet_init_settings(struct net_device *dev)
> @@ -3291,6 +3385,8 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
>  	.set_link_ksettings = virtnet_set_link_ksettings,
>  	.set_coalesce = virtnet_set_coalesce,
>  	.get_coalesce = virtnet_get_coalesce,
> +	.set_per_queue_coalesce = virtnet_set_per_queue_coalesce,
> +	.get_per_queue_coalesce = virtnet_get_per_queue_coalesce,
>  	.get_rxfh_key_size = virtnet_get_rxfh_key_size,
>  	.get_rxfh_indir_size = virtnet_get_rxfh_indir_size,
>  	.get_rxfh = virtnet_get_rxfh,
> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> index 12c1c9699935..cc65ef0f3c3e 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/include/uapi/linux/virtio_net.h
> @@ -56,6 +56,7 @@
>  #define VIRTIO_NET_F_MQ	22	/* Device supports Receive Flow
>  					 * Steering */
>  #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
> +#define VIRTIO_NET_F_VQ_NOTF_COAL 52	/* Device supports virtqueue notification coalescing */
>  #define VIRTIO_NET_F_NOTF_COAL	53	/* Device supports notifications coalescing */
>  #define VIRTIO_NET_F_GUEST_USO4	54	/* Guest can handle USOv4 in. */
>  #define VIRTIO_NET_F_GUEST_USO6	55	/* Guest can handle USOv6 in. */
> @@ -391,5 +392,18 @@ struct virtio_net_ctrl_coal_rx {
>  };
>  
>  #define VIRTIO_NET_CTRL_NOTF_COAL_RX_SET		1
> +#define VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET		2
> +#define VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET		3
> +
> +struct virtio_net_ctrl_coal {
> +	__le32 max_packets;
> +	__le32 max_usecs;
> +};
> +
> +struct  virtio_net_ctrl_coal_vq {
> +	__le16 vqn;
> +	__le16 reserved;
> +	struct virtio_net_ctrl_coal coal;
> +};
>  
>  #endif /* _UAPI_LINUX_VIRTIO_NET_H */
> -- 
> 2.39.1