Subject: Re: [net-next rfc v7 2/3] virtio_net: multiqueue support

From: "Michael S. Tsirkin" <[email-masked]>
Date: Sun, 2 Dec 2012 18:06:31 +0200

On Tue, Nov 27, 2012 at 06:15:59PM +0800, Jason Wang wrote:
> This addes multiqueue support to virtio_net driver. In multiple queue modes, the
> driver expects the number of queue paris is equal to the number of vcpus. To
> eliminate the contention bettwen vcpus and virtqueues, per-cpu virtqueue pairs
> were implemented through:
> 
> - select the txq based on the smp processor id.
> - smp affinity hint were set to the vcpu that owns the queue pairs.
> 
> Signed-off-by: Krishna Kumar <[email-masked]>
> Signed-off-by: Jason Wang <[email-masked]>
> ---
>  drivers/net/virtio_net.c        |  454 ++++++++++++++++++++++++++++++---------
>  include/uapi/linux/virtio_net.h |   16 ++
>  2 files changed, 371 insertions(+), 99 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 7975133..bcaa6e5 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -84,17 +84,25 @@ struct virtnet_info {
>  	struct virtio_device *vdev;
>  	struct virtqueue *cvq;
>  	struct net_device *dev;
> -	struct napi_struct napi;
> -	struct send_queue sq;
> -	struct receive_queue rq;
> +	struct send_queue *sq;
> +	struct receive_queue *rq;
>  	unsigned int status;
>  
> +	/* Max # of queue pairs supported by the device */
> +	u16 max_queue_pairs;
> +
> +	/* # of queue pairs currently used by the driver */
> +	u16 curr_queue_pairs;
> +
>  	/* I like... big packets and I cannot lie! */
>  	bool big_packets;
>  
>  	/* Host will merge rx buffers for big packets (shake it! shake it!) */
>  	bool mergeable_rx_bufs;
>  
> +	/* Has control virtqueue */
> +	bool has_cvq;
> +
>  	/* enable config space updates */
>  	bool config_enable;
>  
> @@ -126,6 +134,34 @@ struct padded_vnet_hdr {
>  	char padding[6];
>  };
>  
> +static const struct ethtool_ops virtnet_ethtool_ops;
> +
> +/*
> + * Converting between virtqueue no. and kernel tx/rx queue no.
> + * 0:rx0 1:tx0 2:cvq 3:rx1 4:tx1 ... 2N+1:rxN 2N+2:txN
> + */

Weird, this isn't what spec v5 says: it says
0:rx0 1:tx0 2: rx1 3: tx1 .... vcq
We can change the spec to match but keeping all rx/tx
together seems a bit prettier?

> +static int vq2txq(struct virtqueue *vq)
> +{
> +	int index = virtqueue_get_queue_index(vq);
> +	return index == 1 ? 0 : (index - 2) / 2;
> +}
> +
> +static int txq2vq(int txq)
> +{
> +	return txq ? 2 * txq + 2 : 1;
> +}
> +
> +static int vq2rxq(struct virtqueue *vq)
> +{
> +	int index = virtqueue_get_queue_index(vq);
> +	return index ? (index - 1) / 2 : 0;
> +}
> +
> +static int rxq2vq(int rxq)
> +{
> +	return rxq ? 2 * rxq + 1 : 0;
> +}
> +
>  static inline struct skb_vnet_hdr *skb_vnet_hdr(struct sk_buff *skb)
>  {
>  	return (struct skb_vnet_hdr *)skb->cb;
> @@ -166,7 +202,7 @@ static void skb_xmit_done(struct virtqueue *vq)
>  	virtqueue_disable_cb(vq);
>  
>  	/* We were probably waiting for more output buffers. */
> -	netif_wake_queue(vi->dev);
> +	netif_wake_subqueue(vi->dev, vq2txq(vq));
>  }
>  
>  static void set_skb_frag(struct sk_buff *skb, struct page *page,
> @@ -503,7 +539,7 @@ static bool try_fill_recv(struct receive_queue *rq, gfp_t gfp)
>  static void skb_recv_done(struct virtqueue *rvq)
>  {
>  	struct virtnet_info *vi = rvq->vdev->priv;
> -	struct receive_queue *rq = &vi->rq;
> +	struct receive_queue *rq = &vi->rq[vq2rxq(rvq)];
>  
>  	/* Schedule NAPI, Suppress further interrupts if successful. */
>  	if (napi_schedule_prep(&rq->napi)) {
> @@ -650,7 +686,8 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb)
>  static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
>  {
>  	struct virtnet_info *vi = netdev_priv(dev);
> -	struct send_queue *sq = &vi->sq;
> +	int qnum = skb_get_queue_mapping(skb);
> +	struct send_queue *sq = &vi->sq[qnum];
>  	int capacity;
>  
>  	/* Free up any pending old buffers before queueing new ones. */
> @@ -664,13 +701,14 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
>  		if (likely(capacity == -ENOMEM)) {
>  			if (net_ratelimit())
>  				dev_warn(&dev->dev,
> -					 "TX queue failure: out of memory\n");
> +					 "TXQ (%d) failure: out of memory\n",
> +					 qnum);
>  		} else {
>  			dev->stats.tx_fifo_errors++;
>  			if (net_ratelimit())
>  				dev_warn(&dev->dev,
> -					 "Unexpected TX queue failure: %d\n",
> -					 capacity);
> +					 "Unexpected TXQ (%d) failure: %d\n",
> +					 qnum, capacity);
>  		}
>  		dev->stats.tx_dropped++;
>  		kfree_skb(skb);
> @@ -685,12 +723,12 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
>  	/* Apparently nice girls don't return TX_BUSY; stop the queue
>  	 * before it gets out of hand.  Naturally, this wastes entries. */
>  	if (capacity < 2+MAX_SKB_FRAGS) {
> -		netif_stop_queue(dev);
> +		netif_stop_subqueue(dev, qnum);
>  		if (unlikely(!virtqueue_enable_cb_delayed(sq->vq))) {
>  			/* More just got used, free them then recheck. */
>  			capacity += free_old_xmit_skbs(sq);
>  			if (capacity >= 2+MAX_SKB_FRAGS) {
> -				netif_start_queue(dev);
> +				netif_start_subqueue(dev, qnum);
>  				virtqueue_disable_cb(sq->vq);
>  			}
>  		}
> @@ -758,23 +796,13 @@ static struct rtnl_link_stats64 *virtnet_stats(struct net_device *dev,
>  static void virtnet_netpoll(struct net_device *dev)
>  {
>  	struct virtnet_info *vi = netdev_priv(dev);
> +	int i;
>  
> -	napi_schedule(&vi->rq.napi);
> +	for (i = 0; i < vi->curr_queue_pairs; i++)
> +		napi_schedule(&vi->rq[i].napi);
>  }
>  #endif
>  
> -static int virtnet_open(struct net_device *dev)
> -{
> -	struct virtnet_info *vi = netdev_priv(dev);
> -
> -	/* Make sure we have some buffers: if oom use wq. */
> -	if (!try_fill_recv(&vi->rq, GFP_KERNEL))
> -		schedule_delayed_work(&vi->rq.refill, 0);
> -
> -	virtnet_napi_enable(&vi->rq);
> -	return 0;
> -}
> -
>  /*
>   * Send command via the control virtqueue and check status.  Commands
>   * supported by the hypervisor, as indicated by feature bits, should
> @@ -830,13 +858,53 @@ static void virtnet_ack_link_announce(struct virtnet_info *vi)
>  	rtnl_unlock();
>  }
>  
> +static int virtnet_set_queues(struct virtnet_info *vi)
> +{
> +	struct scatterlist sg;
> +	struct virtio_net_ctrl_rfs s;
> +	struct net_device *dev = vi->dev;
> +
> +	s.virtqueue_pairs = vi->curr_queue_pairs;
> +	sg_init_one(&sg, &s, sizeof(s));
> +
> +	if (!vi->has_cvq)
> +		return -EINVAL;
> +
> +	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_RFS,
> +				  VIRTIO_NET_CTRL_RFS_VQ_PAIRS_SET, &sg, 1, 0)){
> +		dev_warn(&dev->dev, "Fail to set the number of queue pairs to"
> +			 " %d\n", vi->curr_queue_pairs);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +static int virtnet_open(struct net_device *dev)
> +{
> +	struct virtnet_info *vi = netdev_priv(dev);
> +	int i;
> +
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		/* Make sure we have some buffers: if oom use wq. */
> +		if (!try_fill_recv(&vi->rq[i], GFP_KERNEL))
> +			schedule_delayed_work(&vi->rq[i].refill, 0);
> +		virtnet_napi_enable(&vi->rq[i]);
> +	}
> +
> +	return 0;
> +}
> +
>  static int virtnet_close(struct net_device *dev)
>  {
>  	struct virtnet_info *vi = netdev_priv(dev);
> +	int i;
>  
>  	/* Make sure refill_work doesn't re-enable napi! */
> -	cancel_delayed_work_sync(&vi->rq.refill);
> -	napi_disable(&vi->rq.napi);
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		cancel_delayed_work_sync(&vi->rq[i].refill);
> +		napi_disable(&vi->rq[i].napi);
> +	}
>  
>  	return 0;
>  }
> @@ -948,8 +1016,8 @@ static void virtnet_get_ringparam(struct net_device *dev,
>  {
>  	struct virtnet_info *vi = netdev_priv(dev);
>  
> -	ring->rx_max_pending = virtqueue_get_vring_size(vi->rq.vq);
> -	ring->tx_max_pending = virtqueue_get_vring_size(vi->sq.vq);
> +	ring->rx_max_pending = virtqueue_get_vring_size(vi->rq[0].vq);
> +	ring->tx_max_pending = virtqueue_get_vring_size(vi->sq[0].vq);
>  	ring->rx_pending = ring->rx_max_pending;
>  	ring->tx_pending = ring->tx_max_pending;
>  }
> @@ -967,12 +1035,6 @@ static void virtnet_get_drvinfo(struct net_device *dev,
>  
>  }
>  
> -static const struct ethtool_ops virtnet_ethtool_ops = {
> -	.get_drvinfo = virtnet_get_drvinfo,
> -	.get_link = ethtool_op_get_link,
> -	.get_ringparam = virtnet_get_ringparam,
> -};
> -
>  #define MIN_MTU 68
>  #define MAX_MTU 65535
>  
> @@ -984,6 +1046,20 @@ static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
>  	return 0;
>  }
>  
> +/* To avoid contending a lock hold by a vcpu who would exit to host, select the
> + * txq based on the processor id.
> + */
> +static u16 virtnet_select_queue(struct net_device *dev, struct sk_buff *skb)
> +{
> +	int txq = skb_rx_queue_recorded(skb) ? skb_get_rx_queue(skb) :
> +		  smp_processor_id();
> +
> +	while (unlikely(txq >= dev->real_num_tx_queues))
> +		txq -= dev->real_num_tx_queues;
> +
> +	return txq;
> +}
> +
>  static const struct net_device_ops virtnet_netdev = {
>  	.ndo_open            = virtnet_open,
>  	.ndo_stop   	     = virtnet_close,
> @@ -995,6 +1071,7 @@ static const struct net_device_ops virtnet_netdev = {
>  	.ndo_get_stats64     = virtnet_stats,
>  	.ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
>  	.ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
> +	.ndo_select_queue     = virtnet_select_queue,
>  #ifdef CONFIG_NET_POLL_CONTROLLER
>  	.ndo_poll_controller = virtnet_netpoll,
>  #endif
> @@ -1030,10 +1107,10 @@ static void virtnet_config_changed_work(struct work_struct *work)
>  
>  	if (vi->status & VIRTIO_NET_S_LINK_UP) {
>  		netif_carrier_on(vi->dev);
> -		netif_wake_queue(vi->dev);
> +		netif_tx_wake_all_queues(vi->dev);
>  	} else {
>  		netif_carrier_off(vi->dev);
> -		netif_stop_queue(vi->dev);
> +		netif_tx_stop_all_queues(vi->dev);
>  	}
>  done:
>  	mutex_unlock(&vi->config_lock);
> @@ -1046,41 +1123,212 @@ static void virtnet_config_changed(struct virtio_device *vdev)
>  	schedule_work(&vi->config_work);
>  }
>  
> -static int init_vqs(struct virtnet_info *vi)
> +static void free_receive_bufs(struct virtnet_info *vi)
> +{
> +	int i;
> +
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		while (vi->rq[i].pages)
> +			__free_pages(get_a_page(&vi->rq[i], GFP_KERNEL), 0);
> +	}
> +}
> +
> +/* Free memory allocated for send and receive queues */
> +static void virtnet_free_queues(struct virtnet_info *vi)
>  {
> -	struct virtqueue *vqs[3];
> -	vq_callback_t *callbacks[] = { skb_recv_done, skb_xmit_done, NULL};
> -	const char *names[] = { "input", "output", "control" };
> -	int nvqs, err;
> +	kfree(vi->rq);
> +	vi->rq = NULL;
> +	kfree(vi->sq);
> +	vi->sq = NULL;
> +}
>  
> -	/* We expect two virtqueues, receive then send,
> -	 * and optionally control. */
> -	nvqs = virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ) ? 3 : 2;
> +static void free_unused_bufs(struct virtnet_info *vi)
> +{
> +	void *buf;
> +	int i;
>  
> -	err = vi->vdev->config->find_vqs(vi->vdev, nvqs, vqs, callbacks, names);
> -	if (err)
> -		return err;
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		struct virtqueue *vq = vi->sq[i].vq;
> +		while ((buf = virtqueue_detach_unused_buf(vq)) != NULL)
> +			dev_kfree_skb(buf);
> +	}
>  
> -	vi->rq.vq = vqs[0];
> -	vi->sq.vq = vqs[1];
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		struct virtqueue *vq = vi->rq[i].vq;
>  
> -	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ)) {
> -		vi->cvq = vqs[2];
> +		while ((buf = virtqueue_detach_unused_buf(vq)) != NULL) {
> +			if (vi->mergeable_rx_bufs || vi->big_packets)
> +				give_pages(&vi->rq[i], buf);
> +			else
> +				dev_kfree_skb(buf);
> +			--vi->rq[i].num;
> +		}
> +		BUG_ON(vi->rq[i].num != 0);
> +	}
> +}
>  
> +static void virtnet_set_affinity(struct virtnet_info *vi, bool set)
> +{
> +	int i;
> +
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		int cpu = set ? i : -1;
> +		virtqueue_set_affinity(vi->rq[i].vq, cpu);
> +		virtqueue_set_affinity(vi->sq[i].vq, cpu);
> +	}
> +}
> +
> +static void virtnet_del_vqs(struct virtnet_info *vi)
> +{
> +	struct virtio_device *vdev = vi->vdev;
> +
> +	virtnet_set_affinity(vi, false);
> +
> +	vdev->config->del_vqs(vdev);
> +
> +	virtnet_free_queues(vi);
> +}
> +
> +static int virtnet_find_vqs(struct virtnet_info *vi)
> +{
> +	vq_callback_t **callbacks;
> +	struct virtqueue **vqs;
> +	int ret = -ENOMEM;
> +	int i, total_vqs;
> +	char **names;
> +
> +	/*
> +	 * We expect 1 RX virtqueue followed by 1 TX virtqueue, followd by
> +	 * possible control virtqueue, followed by RX/TX N-1 queue pairs used
> +	 * in multiqueue mode.
> +	 */
> +	total_vqs = vi->max_queue_pairs * 2 +
> +		    virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ);
> +
> +	/* Allocate space for find_vqs parameters */
> +	vqs = kzalloc(total_vqs * sizeof(*vqs), GFP_KERNEL);
> +	callbacks = kzalloc(total_vqs * sizeof(*callbacks), GFP_KERNEL);
> +	if (!vqs || !callbacks)
> +		goto err_mem;
> +	names = kzalloc(total_vqs * sizeof(*names), GFP_KERNEL);
> +	if (!names)
> +		goto err_mem;
> +
> +	/* Parameters for control virtqueue, if any */
> +	if (vi->has_cvq) {
> +		callbacks[2] = NULL;
> +		names[2] = kasprintf(GFP_KERNEL, "control");
> +	}
> +
> +	/* Allocate/initialize parameters for send/receive virtqueues */
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		callbacks[rxq2vq(i)] = skb_recv_done;
> +		callbacks[txq2vq(i)] = skb_xmit_done;
> +		names[rxq2vq(i)] = kasprintf(GFP_KERNEL, "input.%d", i);
> +		names[txq2vq(i)] = kasprintf(GFP_KERNEL, "output.%d", i);
> +	}
> +
> +	ret = vi->vdev->config->find_vqs(vi->vdev, total_vqs, vqs, callbacks,
> +					 (const char **)names);
> +	if (ret)
> +		goto err_names;
> +
> +	if (vi->has_cvq) {
> +		vi->cvq = vqs[2];
>  		if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VLAN))
>  			vi->dev->features |= NETIF_F_HW_VLAN_FILTER;
>  	}
> +
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		vi->rq[i].vq = vqs[rxq2vq(i)];
> +		vi->sq[i].vq = vqs[txq2vq(i)];
> +	}
> +
> +	kfree(callbacks);
> +	kfree(vqs);
> +
> +	return 0;
> +
> +err_names:
> +	for (i = 0; i < total_vqs * 2; i ++)
> +		kfree(names[i]);
> +	kfree(names);
> +
> +err_mem:
> +	kfree(callbacks);
> +	kfree(vqs);
> +
> +	return ret;
> +}
> +
> +static int virtnet_alloc_queues(struct virtnet_info *vi)
> +{
> +	int i;
> +
> +	vi->sq = kzalloc(sizeof(vi->sq[0]) * vi->max_queue_pairs, GFP_KERNEL);
> +	vi->rq = kzalloc(sizeof(vi->rq[0]) * vi->max_queue_pairs, GFP_KERNEL);
> +	if (!vi->rq || !vi->sq)
> +		goto err;
> +
> +	/* setup initial receive and send queue parameters */
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		vi->rq[i].pages = NULL;
> +		INIT_DELAYED_WORK(&vi->rq[i].refill, refill_work);
> +		netif_napi_add(vi->dev, &vi->rq[i].napi, virtnet_poll,
> +			       napi_weight);
> +
> +		sg_init_table(vi->rq[i].sg, ARRAY_SIZE(vi->rq[i].sg));
> +		sg_init_table(vi->sq[i].sg, ARRAY_SIZE(vi->sq[i].sg));
> +	}
> +
> +
>  	return 0;
> +
> +err:
> +	virtnet_free_queues(vi);
> +	return -ENOMEM;
> +}
> +
> +static int init_vqs(struct virtnet_info *vi)
> +{
> +	int ret;
> +
> +	/* Allocate send & receive queues */
> +	ret = virtnet_alloc_queues(vi);
> +	if (ret)
> +		goto err;
> +
> +	ret = virtnet_find_vqs(vi);
> +	if (ret)
> +		goto err_free;
> +
> +	virtnet_set_affinity(vi, true);
> +	return 0;
> +
> +err_free:
> +	virtnet_free_queues(vi);
> +err:
> +	return ret;
>  }
>  
>  static int virtnet_probe(struct virtio_device *vdev)
>  {
> -	int err;
> +	int i, err;
>  	struct net_device *dev;
>  	struct virtnet_info *vi;
> +	u16 curr_queue_pairs;

Probably a good idea to rename this max_queue_pairs.

> +
> +	/* Find if host supports multiqueue virtio_net device */
> +	err = virtio_config_val(vdev, VIRTIO_NET_F_RFS,
> +				offsetof(struct virtio_net_config,
> +				max_virtqueue_pairs), &curr_queue_pairs);
> +
> +	/* We need at least 2 queue's */
> +	if (err)
> +		curr_queue_pairs = 1;

Let's also validate against VIRTIO_NET_CTRL_RFS_VQ_PAIRS_MIN
and VIRTIO_NET_CTRL_RFS_VQ_PAIRS_MAX.

>  
>  	/* Allocate ourselves a network device with room for our info */
> -	dev = alloc_etherdev(sizeof(struct virtnet_info));
> +	dev = alloc_etherdev_mq(sizeof(struct virtnet_info), curr_queue_pairs);
>  	if (!dev)
>  		return -ENOMEM;
>  
> @@ -1126,22 +1374,17 @@ static int virtnet_probe(struct virtio_device *vdev)
>  
>  	/* Set up our device-specific information */
>  	vi = netdev_priv(dev);
> -	netif_napi_add(dev, &vi->rq.napi, virtnet_poll, napi_weight);
>  	vi->dev = dev;
>  	vi->vdev = vdev;
>  	vdev->priv = vi;
> -	vi->rq.pages = NULL;
>  	vi->stats = alloc_percpu(struct virtnet_stats);
>  	err = -ENOMEM;
>  	if (vi->stats == NULL)
>  		goto free;
>  
> -	INIT_DELAYED_WORK(&vi->rq.refill, refill_work);
>  	mutex_init(&vi->config_lock);
>  	vi->config_enable = true;
>  	INIT_WORK(&vi->config_work, virtnet_config_changed_work);
> -	sg_init_table(vi->rq.sg, ARRAY_SIZE(vi->rq.sg));
> -	sg_init_table(vi->sq.sg, ARRAY_SIZE(vi->sq.sg));
>  
>  	/* If we can receive ANY GSO packets, we must allocate large ones. */
>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> @@ -1152,10 +1395,21 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF))
>  		vi->mergeable_rx_bufs = true;
>  
> +	if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ))
> +		vi->has_cvq = true;
> +
> +	/* Use single tx/rx queue pair as default */
> +	vi->curr_queue_pairs = 1;
> +	vi->max_queue_pairs = curr_queue_pairs;
> +
> +	/* Allocate/initialize the rx/tx queues, and invoke find_vqs */
>  	err = init_vqs(vi);
>  	if (err)
>  		goto free_stats;
>  
> +	netif_set_real_num_tx_queues(dev, 1);
> +	netif_set_real_num_rx_queues(dev, 1);
> +
>  	err = register_netdev(dev);
>  	if (err) {
>  		pr_debug("virtio_net: registering device failed\n");
> @@ -1163,12 +1417,15 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	}
>  
>  	/* Last of all, set up some receive buffers. */
> -	try_fill_recv(&vi->rq, GFP_KERNEL);
> -
> -	/* If we didn't even get one input buffer, we're useless. */
> -	if (vi->rq.num == 0) {
> -		err = -ENOMEM;
> -		goto unregister;
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		try_fill_recv(&vi->rq[i], GFP_KERNEL);
> +
> +		/* If we didn't even get one input buffer, we're useless. */
> +		if (vi->rq[i].num == 0) {
> +			free_unused_bufs(vi);
> +			err = -ENOMEM;
> +			goto free_recv_bufs;
> +		}
>  	}
>  
>  	/* Assume link up if device can't report link status,
> @@ -1181,13 +1438,20 @@ static int virtnet_probe(struct virtio_device *vdev)
>  		netif_carrier_on(dev);
>  	}
>  
> -	pr_debug("virtnet: registered device %s\n", dev->name);
> +	pr_debug("virtnet: registered device %s with %d RX and TX vq's\n",
> +		 dev->name, curr_queue_pairs);
> +
>  	return 0;
>  
> -unregister:
> +free_recv_bufs:
> +	free_receive_bufs(vi);
>  	unregister_netdev(dev);
> +
>  free_vqs:
> -	vdev->config->del_vqs(vdev);
> +	for (i = 0; i <curr_queue_pairs; i++)
> +		cancel_delayed_work_sync(&vi->rq[i].refill);
> +	virtnet_del_vqs(vi);
> +
>  free_stats:
>  	free_percpu(vi->stats);
>  free:
> @@ -1195,28 +1459,6 @@ free:
>  	return err;
>  }
>  
> -static void free_unused_bufs(struct virtnet_info *vi)
> -{
> -	void *buf;
> -	while (1) {
> -		buf = virtqueue_detach_unused_buf(vi->sq.vq);
> -		if (!buf)
> -			break;
> -		dev_kfree_skb(buf);
> -	}
> -	while (1) {
> -		buf = virtqueue_detach_unused_buf(vi->rq.vq);
> -		if (!buf)
> -			break;
> -		if (vi->mergeable_rx_bufs || vi->big_packets)
> -			give_pages(&vi->rq, buf);
> -		else
> -			dev_kfree_skb(buf);
> -		--vi->rq.num;
> -	}
> -	BUG_ON(vi->rq.num != 0);
> -}
> -
>  static void remove_vq_common(struct virtnet_info *vi)
>  {
>  	vi->vdev->config->reset(vi->vdev);
> @@ -1224,10 +1466,9 @@ static void remove_vq_common(struct virtnet_info *vi)
>  	/* Free unused buffers in both send and recv, if any. */
>  	free_unused_bufs(vi);
>  
> -	vi->vdev->config->del_vqs(vi->vdev);
> +	free_receive_bufs(vi);
>  
> -	while (vi->rq.pages)
> -		__free_pages(get_a_page(&vi->rq, GFP_KERNEL), 0);
> +	virtnet_del_vqs(vi);
>  }
>  
>  static void __devexit virtnet_remove(struct virtio_device *vdev)
> @@ -1253,6 +1494,7 @@ static void __devexit virtnet_remove(struct virtio_device *vdev)
>  static int virtnet_freeze(struct virtio_device *vdev)
>  {
>  	struct virtnet_info *vi = vdev->priv;
> +	int i;
>  
>  	/* Prevent config work handler from accessing the device */
>  	mutex_lock(&vi->config_lock);
> @@ -1260,10 +1502,14 @@ static int virtnet_freeze(struct virtio_device *vdev)
>  	mutex_unlock(&vi->config_lock);
>  
>  	netif_device_detach(vi->dev);
> -	cancel_delayed_work_sync(&vi->rq.refill);
> +	for (i = 0; i < vi->max_queue_pairs; i++)
> +		cancel_delayed_work_sync(&vi->rq[i].refill);
>  
>  	if (netif_running(vi->dev))
> -		napi_disable(&vi->rq.napi);
> +		for (i = 0; i < vi->max_queue_pairs; i++) {
> +			napi_disable(&vi->rq[i].napi);
> +			netif_napi_del(&vi->rq[i].napi);
> +		}
>  
>  	remove_vq_common(vi);
>  
> @@ -1275,24 +1521,28 @@ static int virtnet_freeze(struct virtio_device *vdev)
>  static int virtnet_restore(struct virtio_device *vdev)
>  {
>  	struct virtnet_info *vi = vdev->priv;
> -	int err;
> +	int err, i;
>  
>  	err = init_vqs(vi);
>  	if (err)
>  		return err;
>  
>  	if (netif_running(vi->dev))
> -		virtnet_napi_enable(&vi->rq);
> +		for (i = 0; i < vi->max_queue_pairs; i++)
> +			virtnet_napi_enable(&vi->rq[i]);
>  
>  	netif_device_attach(vi->dev);
>  
> -	if (!try_fill_recv(&vi->rq, GFP_KERNEL))
> -		schedule_delayed_work(&vi->rq.refill, 0);
> +	for (i = 0; i < vi->max_queue_pairs; i++)
> +		if (!try_fill_recv(&vi->rq[i], GFP_KERNEL))
> +			schedule_delayed_work(&vi->rq[i].refill, 0);
>  
>  	mutex_lock(&vi->config_lock);
>  	vi->config_enable = true;
>  	mutex_unlock(&vi->config_lock);
>  
> +	BUG_ON(virtnet_set_queues(vi));
> +

Won't this always fail when control vq is off?

>  	return 0;
>  }
>  #endif
> @@ -1310,7 +1560,7 @@ static unsigned int features[] = {
>  	VIRTIO_NET_F_GUEST_ECN, VIRTIO_NET_F_GUEST_UFO,
>  	VIRTIO_NET_F_MRG_RXBUF, VIRTIO_NET_F_STATUS, VIRTIO_NET_F_CTRL_VQ,
>  	VIRTIO_NET_F_CTRL_RX, VIRTIO_NET_F_CTRL_VLAN,
> -	VIRTIO_NET_F_GUEST_ANNOUNCE,
> +	VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_RFS,
>  };
>  
>  static struct virtio_driver virtio_net_driver = {
> @@ -1328,6 +1578,12 @@ static struct virtio_driver virtio_net_driver = {
>  #endif
>  };
>  
> +static const struct ethtool_ops virtnet_ethtool_ops = {
> +	.get_drvinfo = virtnet_get_drvinfo,
> +	.get_link = ethtool_op_get_link,
> +	.get_ringparam = virtnet_get_ringparam,
> +};
> +
>  static int __init init(void)
>  {
>  	return register_virtio_driver(&virtio_net_driver);
> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> index 2470f54..6056cec 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/include/uapi/linux/virtio_net.h
> @@ -51,6 +51,7 @@
>  #define VIRTIO_NET_F_CTRL_RX_EXTRA 20	/* Extra RX mode control support */
>  #define VIRTIO_NET_F_GUEST_ANNOUNCE 21	/* Guest can announce device on the
>  					 * network */
> +#define VIRTIO_NET_F_RFS	22	/* Device supports multiple TXQ/RXQ */
>  
>  #define VIRTIO_NET_S_LINK_UP	1	/* Link is up */
>  #define VIRTIO_NET_S_ANNOUNCE	2	/* Announcement is needed */
> @@ -60,6 +61,8 @@ struct virtio_net_config {
>  	__u8 mac[6];
>  	/* See VIRTIO_NET_F_STATUS and VIRTIO_NET_S_* above */
>  	__u16 status;
> +	/* Total number of RX/TX queues */
> +	__u16 max_virtqueue_pairs;
>  } __attribute__((packed));
>  
>  /* This is the first element of the scatter-gather list.  If you don't
> @@ -166,4 +169,17 @@ struct virtio_net_ctrl_mac {
>  #define VIRTIO_NET_CTRL_ANNOUNCE       3
>   #define VIRTIO_NET_CTRL_ANNOUNCE_ACK         0
>  
> +/*
> + * Control multiqueue
> + *
> + */
> +struct virtio_net_ctrl_rfs {
> +	u16 virtqueue_pairs;
> +};
> +
> +#define VIRTIO_NET_CTRL_RFS   4
> + #define VIRTIO_NET_CTRL_RFS_VQ_PAIRS_SET        0
> + #define VIRTIO_NET_CTRL_RFS_VQ_PAIRS_MIN        1
> + #define VIRTIO_NET_CTRL_RFS_VQ_PAIRS_MAX        0x8000
> +
>  #endif /* _LINUX_VIRTIO_NET_H */
> -- 
> 1.7.1