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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 4 Dec 2012 15:24:22 +0200

I found some bugs, see below.
Also some style nitpicking, this is not mandatory to address.

On Tue, Dec 04, 2012 at 07:07:57PM +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:

Lots of typos above - try running ispell on it :)

> 
> - 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        |  472 ++++++++++++++++++++++++++++++---------
>  include/uapi/linux/virtio_net.h |   16 ++
>  2 files changed, 385 insertions(+), 103 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 266f712..912f5b2 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -81,16 +81,25 @@ struct virtnet_info {
>  	struct virtio_device *vdev;
>  	struct virtqueue *cvq;
>  	struct net_device *dev;
> -	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;
>  
> @@ -125,6 +134,32 @@ 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:rx1 3:tx1 ... 2N:rxN 2N+1:txN 2N+2:cvq
> + */
> +static int vq2txq(struct virtqueue *vq)
> +{
> +	return (virtqueue_get_queue_index(vq) - 1) / 2;
> +}
> +
> +static int txq2vq(int txq)
> +{
> +	return txq * 2 + 1;
> +}
> +
> +static int vq2rxq(struct virtqueue *vq)
> +{
> +	return virtqueue_get_queue_index(vq) / 2;
> +}
> +
> +static int rxq2vq(int rxq)
> +{
> +	return rxq * 2;
> +}
> +
>  static inline struct skb_vnet_hdr *skb_vnet_hdr(struct sk_buff *skb)
>  {
>  	return (struct skb_vnet_hdr *)skb->cb;
> @@ -165,7 +200,7 @@ 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,
> @@ -502,7 +537,7 @@ 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)) {
> @@ -532,15 +567,21 @@ static void refill_work(struct work_struct *work)
>  	struct virtnet_info *vi =
>  		container_of(work, struct virtnet_info, refill.work);
>  	bool still_empty;
> +	int i;
> +
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		struct receive_queue *rq = &vi->rq[i];
>  
> -	napi_disable(&vi->rq.napi);
> -	still_empty = !try_fill_recv(&vi->rq, GFP_KERNEL);
> -	virtnet_napi_enable(&vi->rq);
> +		napi_disable(&rq->napi);
> +		still_empty = !try_fill_recv(rq, GFP_KERNEL);
> +		virtnet_napi_enable(rq);
>  
> -	/* In theory, this can happen: if we don't get any buffers in
> -	 * we will *never* try to fill again. */
> -	if (still_empty)
> -		schedule_delayed_work(&vi->refill, HZ/2);
> +		/* In theory, this can happen: if we don't get any buffers in
> +		 * we will *never* try to fill again.
> +		 */
> +		if (still_empty)
> +			schedule_delayed_work(&vi->refill, HZ/2);
> +	}
>  }
>  
>  static int virtnet_poll(struct napi_struct *napi, int budget)
> @@ -650,7 +691,8 @@ 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 +706,14 @@ 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 +728,12 @@ 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 +801,13 @@ 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->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 +863,51 @@ static void virtnet_ack_link_announce(struct virtnet_info *vi)
>  	rtnl_unlock();
>  }
>  
> +/* Caller check the support of cvq and multiqueue. */
> +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 (!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 num of queue pairs to %d\n",
> +			 vi->curr_queue_pairs);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +static int virtnet_open(struct net_device *dev)

Why move this here? diff will be smaller if you don't.

> +{
> +	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->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->refill);
> -	napi_disable(&vi->rq.napi);
> +
> +	for (i = 0; i < vi->max_queue_pairs; i++)
> +		napi_disable(&vi->rq[i].napi);
>  
>  	return 0;
>  }
> @@ -948,8 +1019,8 @@ 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 +1038,6 @@ 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 +1049,21 @@ 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.
> + * TODO: handle cpu hotplug.
> + */
> +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 +1075,7 @@ 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 +1111,10 @@ 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 +1127,219 @@ 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)
>  {
> -	struct virtqueue *vqs[3];
> -	vq_callback_t *callbacks[] = { skb_recv_done, skb_xmit_done, NULL};
> -	const char *names[] = { "input", "output", "control" };
> -	int nvqs, err;
> +	int i;
>  
> -	/* We expect two virtqueues, receive then send,
> -	 * and optionally control. */
> -	nvqs = virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ) ? 3 : 2;
> +	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);
> +	}
> +}
>  
> -	err = vi->vdev->config->find_vqs(vi->vdev, nvqs, vqs, callbacks, names);
> -	if (err)
> -		return err;
> +/* Free memory allocated for send and receive queues */
> +static void virtnet_free_queues(struct virtnet_info *vi)

I think it's cleaner to open-code this, this way
during error handling you can have:

	kfree(vi->rq);
err_rq:
	kfree(vi->sq);
err_sq:

without tricks like malloc them both then goto end.

> +{
> +	kfree(vi->rq);
> +	vi->rq = NULL;
> +	kfree(vi->sq);
> +	vi->sq = NULL;

I think = NULL is not needed - we never call this twice.

> +}
> +
> +static void free_unused_bufs(struct virtnet_info *vi)
> +{
> +	void *buf;
> +	int i;
> +
> +	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);
> +	}
> +
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		struct virtqueue *vq = vi->rq[i].vq;
> +
> +		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;
> +
> +	/* Don't set the affinity hint when in single queue mode or we have too
> +	 * much online cpus.
> +	 */

Pls remove this comment, or replace with one explaining
the motivation for this logic.

> +	if (vi->curr_queue_pairs == 1 ||
> +	    vi->max_queue_pairs > num_online_cpus())

If we have less it's not a good idea either, is it?
So check vi->max_queue_pairs != num_online_cpus().

> +		set = false;

This will overwrite affinity if it was set by userspace.
Just
	if (set)
		return;
will not have this problem.

> +	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)

It might be a good idea to add this function in previous
patch.

> +{
> +	struct virtio_device *vdev = vi->vdev;
> +
> +	virtnet_set_affinity(vi, false);
> +
> +	vdev->config->del_vqs(vdev);
>  
> -	vi->rq.vq = vqs[0];
> -	vi->sq.vq = vqs[1];
> +	virtnet_free_queues(vi);
> +}
>  
> -	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ)) {
> -		vi->cvq = vqs[2];
> +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

followed

> +	 * possible N-1 RX/TX queue pairs used in multiqueue mode, followed by
> +	 * possible control vq.
> +	 */
> +	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);

Why kzalloc? You seem to fill in all of it. Pls just use kmalloc
and initialize fields.

> +	if (!names)
> +		goto err_mem;

Since you have separate goto here it's more consistent
to use a separate label and two if tests above.

> +
> +	/* Parameters for control virtqueue, if any */
> +	if (vi->has_cvq) {
> +		callbacks[total_vqs - 1] = NULL;
> +		names[total_vqs - 1] = 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);
> +	}

We would need to check kasprintf return value.
Also if you allocate names from slab we'll need to free them
later.
It's probably easier to just use fixed names for now -
it's not like the index is really useful.

> +
> +	ret = vi->vdev->config->find_vqs(vi->vdev, total_vqs, vqs, callbacks,
> +					 (const char **)names);

Please avoid casts, use a proper type for names.

> +	if (ret)
> +		goto err_names;
> +
> +	if (vi->has_cvq) {
> +		vi->cvq = vqs[total_vqs - 1];
>  		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);

Who frees names if there's no error?

> +
> +	return 0;
> +
> +err_names:
> +	for (i = 0; i < total_vqs * 2; i++)

Why * 2?
This looks like a bug.

> +		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);

While equivalent, *vi->rq is clearer IMHO.

> +	if (!vi->rq || !vi->sq)
> +		goto err;
> +
> +	INIT_DELAYED_WORK(&vi->refill, refill_work);
> +	/* setup initial receive and send queue parameters */

Pls remove this comment, it's confuses more than it clarifies.

> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		vi->rq[i].pages = NULL;
> +		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));
> +	}
> +
> +

Extra empty line.

> +	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 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), &max_queue_pairs);
> +
> +	/* We need at least 2 queue's */
> +	if (err || max_queue_pairs < VIRTIO_NET_CTRL_RFS_VQ_PAIRS_MIN ||
> +	    max_queue_pairs > VIRTIO_NET_CTRL_RFS_VQ_PAIRS_MAX)

Check has_cvq as well.

> +		max_queue_pairs = 1;
>  
>  	/* 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), max_queue_pairs);
>  	if (!dev)
>  		return -ENOMEM;
>  
> @@ -1127,22 +1386,17 @@ 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->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) ||
> @@ -1153,10 +1407,21 @@ 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 = max_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");
> @@ -1164,12 +1429,15 @@ 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,
> @@ -1182,13 +1450,19 @@ 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, max_queue_pairs);
> +
>  	return 0;
>  
> -unregister:
> +free_recv_bufs:
> +	free_receive_bufs(vi);
>  	unregister_netdev(dev);
> +
>  free_vqs:
> -	vdev->config->del_vqs(vdev);
> +	cancel_delayed_work_sync(&vi->refill);
> +	virtnet_del_vqs(vi);
> +
>  free_stats:
>  	free_percpu(vi->stats);
>  free:
> @@ -1196,28 +1470,6 @@ 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);
> @@ -1225,10 +1477,9 @@ 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)
> @@ -1254,6 +1505,7 @@ 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);
> @@ -1264,7 +1516,10 @@ static int virtnet_freeze(struct virtio_device *vdev)
>  	cancel_delayed_work_sync(&vi->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);
>  
> @@ -1276,24 +1531,29 @@ 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->refill, 0);
> +	for (i = 0; i < vi->max_queue_pairs; i++)
> +		if (!try_fill_recv(&vi->rq[i], GFP_KERNEL))
> +			schedule_delayed_work(&vi->refill, 0);
>  
>  	mutex_lock(&vi->config_lock);
>  	vi->config_enable = true;
>  	mutex_unlock(&vi->config_lock);
>  
> +	if (vi->has_cvq && virtio_has_feature(vi->vdev, VIRTIO_NET_F_RFS))
> +		virtnet_set_queues(vi);
> +

I think it's easier to test
if (curr_queue_pairs == max_queue_pairs)
within virtnet_set_queues and make it
a NOP if so.

>  	return 0;
>  }
>  #endif
> @@ -1311,7 +1571,7 @@ 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 = {
> @@ -1329,6 +1589,12 @@ 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 */

Should be
/* Device supports Receive Flow Steering. */

>  
>  #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 */

Better comment:
/* Maximum number of each of transmit and receive queues;
 * see VIRTIO_NET_F_RFS and VIRTIO_NET_CTRL_RFS.
 * Legal values are between 1 and 0x8000
 */

> +	__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

Here's a better comment:

Control Receive Flow Steering

 The command VIRTIO_NET_CTRL_RFS_VQ_PAIRS_SET
 enables Receive Flow Steering, specifying the number of the transmit and receive queues that
will be used.
 After the command is consumed and acked by the device,
 the device will not steer new packets on receive virtqueues
 other than specified nor read from transmit virtqueues other than specified.
 Accordingly, driver should not transmit new packets
 on virtqueues other than specified.

> + *

Remove this empty line.

> + */
> +struct virtio_net_ctrl_rfs {
/* Number of each of transmit and receive queues to use;
 * Legal values are between 1 and max_virtqueue_pairs
 */
> +	u16 virtqueue_pairs;
> +};
> +
> +#define VIRTIO_NET_CTRL_RFS   4
> + #define VIRTIO_NET_CTRL_RFS_VQ_PAIRS_SET        0

/* Value range for max_virtqueue_pairsfor and virtqueue_pairs above */

> + #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