Subject: Re: [net-next RFC V5 5/5] virtio_net: support negotiating the number of queues through ctrl vq

From: "Michael S. Tsirkin" <[email-masked]>
Date: Fri, 20 Jul 2012 15:33:20 +0300

On Thu, Jul 05, 2012 at 06:29:54PM +0800, Jason Wang wrote:
> This patch let the virtio_net driver can negotiate the number of queues it
> wishes to use through control virtqueue and export an ethtool interface to let
> use tweak it.
> 
> As current multiqueue virtio-net implementation has optimizations on per-cpu
> virtuqueues, so only two modes were support:
> 
> - single queue pair mode
> - multiple queue paris mode, the number of queues matches the number of vcpus
> 
> The single queue mode were used by default currently due to regression of
> multiqueue mode in some test (especially in stream test).
> 
> Since virtio core does not support paritially deleting virtqueues, so during
> mode switching the whole virtqueue were deleted and the driver would re-create
> the virtqueues it would used.
> 
> btw. The queue number negotiating were defered to .ndo_open(), this is because
> only after feature negotitaion could we send the command to control virtqueue
> (as it may also use event index).
> 
> Signed-off-by: Jason Wang <[email-masked]>
> ---
>  drivers/net/virtio_net.c   |  171 ++++++++++++++++++++++++++++++++++---------
>  include/linux/virtio_net.h |    7 ++
>  2 files changed, 142 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 7410187..3339eeb 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -88,6 +88,7 @@ struct receive_queue {
>  
>  struct virtnet_info {
>  	u16 num_queue_pairs;		/* # of RX/TX vq pairs */
> +	u16 total_queue_pairs;
>  
>  	struct send_queue *sq[MAX_QUEUES] ____cacheline_aligned_in_smp;
>  	struct receive_queue *rq[MAX_QUEUES] ____cacheline_aligned_in_smp;
> @@ -137,6 +138,8 @@ struct padded_vnet_hdr {
>  	char padding[6];
>  };
>  
> +static const struct ethtool_ops virtnet_ethtool_ops;
> +
>  static inline int txq_get_qnum(struct virtnet_info *vi, struct virtqueue *vq)
>  {
>  	int ret = virtqueue_get_queue_index(vq);
> @@ -802,22 +805,6 @@ static void virtnet_netpoll(struct net_device *dev)
>  }
>  #endif
>  
> -static int virtnet_open(struct net_device *dev)
> -{
> -	struct virtnet_info *vi = netdev_priv(dev);
> -	int i;
> -
> -	for (i = 0; i < vi->num_queue_pairs; i++) {
> -		/* Make sure we have some buffers: if oom use wq. */
> -		if (!try_fill_recv(vi->rq[i], GFP_KERNEL))
> -			queue_delayed_work(system_nrt_wq,
> -					   &vi->rq[i]->refill, 0);
> -		virtnet_napi_enable(vi->rq[i]);
> -	}
> -
> -	return 0;
> -}
> -
>  /*
>   * Send command via the control virtqueue and check status.  Commands
>   * supported by the hypervisor, as indicated by feature bits, should
> @@ -873,6 +860,43 @@ 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 net_device *dev = vi->dev;
> +	sg_init_one(&sg, &vi->num_queue_pairs, sizeof(vi->num_queue_pairs));
> +
> +	if (!vi->has_cvq)
> +		return -EINVAL;
> +
> +	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_MULTIQUEUE,
> +				  VIRTIO_NET_CTRL_MULTIQUEUE_QNUM, &sg, 1, 0)){
> +		dev_warn(&dev->dev, "Fail to set the number of queue pairs to"
> +			 " %d\n", vi->num_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->num_queue_pairs; i++) {
> +		/* Make sure we have some buffers: if oom use wq. */
> +		if (!try_fill_recv(vi->rq[i], GFP_KERNEL))
> +			queue_delayed_work(system_nrt_wq,
> +					   &vi->rq[i]->refill, 0);
> +		virtnet_napi_enable(vi->rq[i]);
> +	}
> +
> +	virtnet_set_queues(vi);
> +
> +	return 0;
> +}
> +
>  static int virtnet_close(struct net_device *dev)
>  {
>  	struct virtnet_info *vi = netdev_priv(dev);
> @@ -1013,12 +1037,6 @@ 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
>  
> @@ -1235,7 +1253,7 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
>  
>  err:
>  	if (ret && names)
> -		for (i = 0; i < vi->num_queue_pairs * 2; i++)
> +		for (i = 0; i < total_vqs * 2; i++)
>  			kfree(names[i]);
>  
>  	kfree(names);
> @@ -1373,7 +1391,6 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	mutex_init(&vi->config_lock);
>  	vi->config_enable = true;
>  	INIT_WORK(&vi->config_work, virtnet_config_changed_work);
> -	vi->num_queue_pairs = num_queue_pairs;
>  
>  	/* If we can receive ANY GSO packets, we must allocate large ones. */
>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> @@ -1387,6 +1404,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ))
>  		vi->has_cvq = true;
>  
> +	/* Use single tx/rx queue pair as default */
> +	vi->num_queue_pairs = 1;
> +	vi->total_queue_pairs = num_queue_pairs;
> +
>  	/* Allocate/initialize the rx/tx queues, and invoke find_vqs */
>  	err = virtnet_setup_vqs(vi);
>  	if (err)
> @@ -1396,6 +1417,9 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VLAN))
>  		dev->features |= NETIF_F_HW_VLAN_FILTER;
>  
> +	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");
> @@ -1403,7 +1427,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	}
>  
>  	/* Last of all, set up some receive buffers. */
> -	for (i = 0; i < num_queue_pairs; i++) {
> +	for (i = 0; i < vi->num_queue_pairs; i++) {
>  		try_fill_recv(vi->rq[i], GFP_KERNEL);
>  
>  		/* If we didn't even get one input buffer, we're useless. */
> @@ -1474,10 +1498,8 @@ static void __devexit virtnet_remove(struct virtio_device *vdev)
>  	free_netdev(vi->dev);
>  }
>  
> -#ifdef CONFIG_PM
> -static int virtnet_freeze(struct virtio_device *vdev)
> +static void virtnet_stop(struct virtnet_info *vi)
>  {
> -	struct virtnet_info *vi = vdev->priv;
>  	int i;
>  
>  	/* Prevent config work handler from accessing the device */
> @@ -1493,17 +1515,10 @@ static int virtnet_freeze(struct virtio_device *vdev)
>  		for (i = 0; i < vi->num_queue_pairs; i++)
>  			napi_disable(&vi->rq[i]->napi);
>  
> -
> -	remove_vq_common(vi);
> -
> -	flush_work(&vi->config_work);
> -
> -	return 0;
>  }
>  
> -static int virtnet_restore(struct virtio_device *vdev)
> +static int virtnet_start(struct virtnet_info *vi)
>  {
> -	struct virtnet_info *vi = vdev->priv;
>  	int err, i;
>  
>  	err = virtnet_setup_vqs(vi);
> @@ -1527,6 +1542,29 @@ static int virtnet_restore(struct virtio_device *vdev)
>  
>  	return 0;
>  }
> +
> +#ifdef CONFIG_PM
> +static int virtnet_freeze(struct virtio_device *vdev)
> +{
> +	struct virtnet_info *vi = vdev->priv;
> +
> +	virtnet_stop(vi);
> +
> +	remove_vq_common(vi);
> +
> +	flush_work(&vi->config_work);
> +
> +	return 0;
> +}
> +
> +static int virtnet_restore(struct virtio_device *vdev)
> +{
> +	struct virtnet_info *vi = vdev->priv;
> +
> +	virtnet_start(vi);
> +
> +	return 0;
> +}
>  #endif
>  
>  static struct virtio_device_id id_table[] = {
> @@ -1560,6 +1598,67 @@ static struct virtio_driver virtio_net_driver = {
>  #endif
>  };
>  
> +static int virtnet_set_channels(struct net_device *dev,
> +				struct ethtool_channels *channels)
> +{
> +	struct virtnet_info *vi = netdev_priv(dev);
> +	u16 queues = channels->rx_count;
> +	unsigned status = VIRTIO_CONFIG_S_ACKNOWLEDGE | VIRTIO_CONFIG_S_DRIVER;
> +
> +	if (channels->rx_count != channels->tx_count)
> +		return -EINVAL;
> +	/* Only two modes were support currently */

s/were/are/ ?

> +	if (queues != vi->total_queue_pairs && queues != 1)
> +		return -EINVAL;

So userspace has to get queue number right. How does it know
what the valid value is?

> +	if (!vi->has_cvq)
> +		return -EINVAL;
> +
> +	virtnet_stop(vi);
> +
> +	netif_set_real_num_tx_queues(dev, queues);
> +	netif_set_real_num_rx_queues(dev, queues);
> +
> +	remove_vq_common(vi);
> +	flush_work(&vi->config_work);
> +
> +	vi->num_queue_pairs = queues;
> +	virtnet_start(vi);
> +
> +	vi->vdev->config->finalize_features(vi->vdev);
> +
> +	if (virtnet_set_queues(vi))
> +		status |= VIRTIO_CONFIG_S_FAILED;
> +	else
> +		status |= VIRTIO_CONFIG_S_DRIVER_OK;
> +
> +	vi->vdev->config->set_status(vi->vdev, status);
> +

Why do we need to tweak status like that?
Can we maybe just roll changes back on error?

> +	return 0;
> +}
> +
> +static void virtnet_get_channels(struct net_device *dev,
> +				 struct ethtool_channels *channels)
> +{
> +	struct virtnet_info *vi = netdev_priv(dev);
> +
> +	channels->max_rx = vi->total_queue_pairs;
> +	channels->max_tx = vi->total_queue_pairs;
> +	channels->max_other = 0;
> +	channels->max_combined = 0;
> +	channels->rx_count = vi->num_queue_pairs;
> +	channels->tx_count = vi->num_queue_pairs;
> +	channels->other_count = 0;
> +	channels->combined_count = 0;
> +}
> +
> +static const struct ethtool_ops virtnet_ethtool_ops = {
> +	.get_drvinfo = virtnet_get_drvinfo,
> +	.get_link = ethtool_op_get_link,
> +	.get_ringparam = virtnet_get_ringparam,
> +	.set_channels = virtnet_set_channels,
> +	.get_channels = virtnet_get_channels,
> +};
> +
>  static int __init init(void)
>  {
>  	return register_virtio_driver(&virtio_net_driver);
> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
> index 60f09ff..0d21e08 100644
> --- a/include/linux/virtio_net.h
> +++ b/include/linux/virtio_net.h
> @@ -169,4 +169,11 @@ struct virtio_net_ctrl_mac {
>  #define VIRTIO_NET_CTRL_ANNOUNCE       3
>   #define VIRTIO_NET_CTRL_ANNOUNCE_ACK         0
>  
> +/*
> + * Control multiqueue
> + *
> + */
> +#define VIRTIO_NET_CTRL_MULTIQUEUE       4
> + #define VIRTIO_NET_CTRL_MULTIQUEUE_QNUM         0
> +
>  #endif /* _LINUX_VIRTIO_NET_H */
> -- 
> 1.7.1