Subject: Re: [PATCH] virtio-net: Reporting traffic queue distribution statistics through ethtool

From: "Michael S. Tsirkin" <[email-masked]>
Date: Sun, 19 May 2013 14:28:00 +0300

On Thu, May 16, 2013 at 01:24:29PM -0700, Sriram Narasimhan wrote:
> This patch allows virtio-net driver to report traffic distribution
> to inbound/outbound queues through ethtool -S.  The per_cpu
> virtnet_stats is split into receive and transmit stats and are
> maintained on a per receive_queue and send_queue basis.
> virtnet_stats() is modified to aggregate interface level statistics
> from per-queue statistics.  Sample output below:
> 

Thanks for the patch. The idea itself looks OK to me.
Ben Hutchings already sent some comments
so I won't repeat them. Some minor more comments
and questions below.

> NIC statistics:
>      rxq0: rx_packets: 4357802
>      rxq0: rx_bytes: 292642052
>      txq0: tx_packets: 824540
>      txq0: tx_bytes: 55256404
>      rxq1: rx_packets: 0
>      rxq1: rx_bytes: 0
>      txq1: tx_packets: 1094268
>      txq1: tx_bytes: 73328316
>      rxq2: rx_packets: 0
>      rxq2: rx_bytes: 0
>      txq2: tx_packets: 1091466
>      txq2: tx_bytes: 73140566
>      rxq3: rx_packets: 0
>      rxq3: rx_bytes: 0
>      txq3: tx_packets: 1093043
>      txq3: tx_bytes: 73246142

Interesting. This example implies that all packets are coming in
through the same RX queue - is this right?
If yes that's worth exploring - could be a tun bug -
and shows how this patch is useful.

> Signed-off-by: Sriram Narasimhan <[email-masked]>

BTW, while you are looking at the stats, one other interesting
thing to add could be checking more types of stats: number of exits,
queue full errors, etc.

> ---
>  drivers/net/virtio_net.c |  157 +++++++++++++++++++++++++++++++++++++---------
>  1 files changed, 128 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 3c23fdc..3c58c52 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -41,15 +41,46 @@ module_param(gso, bool, 0444);
>  
>  #define VIRTNET_DRIVER_VERSION "1.0.0"
>  
> -struct virtnet_stats {
> -	struct u64_stats_sync tx_syncp;
> +struct virtnet_rx_stats {
>  	struct u64_stats_sync rx_syncp;
> -	u64 tx_bytes;
> +	u64 rx_packets;
> +	u64 rx_bytes;
> +};
> +
> +struct virtnet_tx_stats {
> +	struct u64_stats_sync tx_syncp;
>  	u64 tx_packets;
> +	u64 tx_bytes;
> +};
>  
> -	u64 rx_bytes;
> -	u64 rx_packets;

I think maintaining the stats in a per-queue data structure like this is
fine.  if # of CPUs == # of queues which is typical, we use same amount
of memory.  And each queue access is under a lock,
or from napi thread, so no races either.

> +struct virtnet_ethtool_stats {
> +	char desc[ETH_GSTRING_LEN];
> +	int type;
> +	int size;
> +	int offset;
> +};
> +
> +enum {VIRTNET_STATS_TX, VIRTNET_STATS_RX};
> +
> +#define VIRTNET_RX_STATS_INFO(_struct, _field) \
> +	{#_field, VIRTNET_STATS_RX, FIELD_SIZEOF(_struct, _field), \
> +	offsetof(_struct, _field)}
> +
> +#define VIRTNET_TX_STATS_INFO(_struct, _field) \
> +	{#_field, VIRTNET_STATS_TX, FIELD_SIZEOF(_struct, _field), \
> +	offsetof(_struct, _field)}
> +
> +static const struct virtnet_ethtool_stats virtnet_et_rx_stats[] = {
> +	VIRTNET_RX_STATS_INFO(struct virtnet_rx_stats, rx_packets),
> +	VIRTNET_RX_STATS_INFO(struct virtnet_rx_stats, rx_bytes)
> +};
> +#define VIRTNET_RX_STATS_NUM (ARRAY_SIZE(virtnet_et_rx_stats))
> +
> +static const struct virtnet_ethtool_stats virtnet_et_tx_stats[] = {
> +	VIRTNET_TX_STATS_INFO(struct virtnet_tx_stats, tx_packets),
> +	VIRTNET_TX_STATS_INFO(struct virtnet_tx_stats, tx_bytes)
>  };
> +#define VIRTNET_TX_STATS_NUM (ARRAY_SIZE(virtnet_et_tx_stats))

I'd prefer a full name: virtnet_ethtool_tx_stats, or
just virtnet_tx_stats.

>  
>  /* Internal representation of a send virtqueue */
>  struct send_queue {
> @@ -61,6 +92,9 @@ struct send_queue {
>  
>  	/* Name of the send queue: output.$index */
>  	char name[40];
> +
> +	/* Active send queue statistics */
> +	struct virtnet_tx_stats stats;
>  };
>  
>  /* Internal representation of a receive virtqueue */
> @@ -81,6 +115,9 @@ struct receive_queue {
>  
>  	/* Name of this receive queue: input.$index */
>  	char name[40];
> +
> +	/* Active receive queue statistics */
> +	struct virtnet_rx_stats stats;
>  };
>  
>  struct virtnet_info {
> @@ -109,9 +146,6 @@ struct virtnet_info {
>  	/* enable config space updates */
>  	bool config_enable;
>  
> -	/* Active statistics */
> -	struct virtnet_stats __percpu *stats;
> -
>  	/* Work struct for refilling if we run low on memory. */
>  	struct delayed_work refill;
>  
> @@ -330,7 +364,7 @@ static void receive_buf(struct receive_queue *rq, void *buf, unsigned int len)
>  {
>  	struct virtnet_info *vi = rq->vq->vdev->priv;
>  	struct net_device *dev = vi->dev;
> -	struct virtnet_stats *stats = this_cpu_ptr(vi->stats);
> +	struct virtnet_rx_stats *stats = &rq->stats;
>  	struct sk_buff *skb;
>  	struct page *page;
>  	struct skb_vnet_hdr *hdr;
> @@ -650,8 +684,7 @@ static void free_old_xmit_skbs(struct send_queue *sq)
>  {
>  	struct sk_buff *skb;
>  	unsigned int len;
> -	struct virtnet_info *vi = sq->vq->vdev->priv;
> -	struct virtnet_stats *stats = this_cpu_ptr(vi->stats);
> +	struct virtnet_tx_stats *stats = &sq->stats;
>  
>  	while ((skb = virtqueue_get_buf(sq->vq, &len)) != NULL) {
>  		pr_debug("Sent skb %p\n", skb);
> @@ -841,24 +874,25 @@ static struct rtnl_link_stats64 *virtnet_stats(struct net_device *dev,
>  					       struct rtnl_link_stats64 *tot)
>  {
>  	struct virtnet_info *vi = netdev_priv(dev);
> -	int cpu;
> +	int i;
>  	unsigned int start;
>  
> -	for_each_possible_cpu(cpu) {
> -		struct virtnet_stats *stats = per_cpu_ptr(vi->stats, cpu);
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		struct virtnet_tx_stats *tstats = &vi->sq[i].stats;
> +		struct virtnet_rx_stats *rstats = &vi->rq[i].stats;
>  		u64 tpackets, tbytes, rpackets, rbytes;
>  
>  		do {
> -			start = u64_stats_fetch_begin_bh(&stats->tx_syncp);
> -			tpackets = stats->tx_packets;
> -			tbytes   = stats->tx_bytes;
> -		} while (u64_stats_fetch_retry_bh(&stats->tx_syncp, start));
> +			start = u64_stats_fetch_begin_bh(&tstats->tx_syncp);
> +			tpackets = tstats->tx_packets;
> +			tbytes   = tstats->tx_bytes;
> +		} while (u64_stats_fetch_retry_bh(&tstats->tx_syncp, start));
>  
>  		do {
> -			start = u64_stats_fetch_begin_bh(&stats->rx_syncp);
> -			rpackets = stats->rx_packets;
> -			rbytes   = stats->rx_bytes;
> -		} while (u64_stats_fetch_retry_bh(&stats->rx_syncp, start));
> +			start = u64_stats_fetch_begin_bh(&rstats->rx_syncp);
> +			rpackets = rstats->rx_packets;
> +			rbytes   = rstats->rx_bytes;
> +		} while (u64_stats_fetch_retry_bh(&rstats->rx_syncp, start));
>  
>  		tot->rx_packets += rpackets;
>  		tot->tx_packets += tpackets;
> @@ -1177,12 +1211,83 @@ static void virtnet_get_channels(struct net_device *dev,
>  	channels->other_count = 0;
>  }
>  
> +static void virtnet_get_stat_strings(struct net_device *dev,
> +					u32 stringset,
> +					u8 *data)
> +{
> +	struct virtnet_info *vi = netdev_priv(dev);
> +	int i, j;
> +
> +	switch (stringset) {
> +	case ETH_SS_STATS:
> +		for (i = 0; i < vi->max_queue_pairs; i++) {
> +			for (j = 0; j < VIRTNET_RX_STATS_NUM; j++) {
> +				sprintf(data, "rxq%d: %s", i,
> +					virtnet_et_rx_stats[j].desc);
> +				data += ETH_GSTRING_LEN;
> +			}
> +			for (j = 0; j < VIRTNET_TX_STATS_NUM; j++) {
> +				sprintf(data, "txq%d: %s", i,
> +					virtnet_et_tx_stats[j].desc);
> +				data += ETH_GSTRING_LEN;
> +			}
> +		}
> +		break;
> +	}
> +}
> +
> +static int virtnet_get_sset_count(struct net_device *dev, int stringset)
> +{
> +	struct virtnet_info *vi = netdev_priv(dev);
> +	switch (stringset) {
> +	case ETH_SS_STATS:
> +		return vi->max_queue_pairs *
> +			(VIRTNET_RX_STATS_NUM + VIRTNET_TX_STATS_NUM);
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static void virtnet_get_ethtool_stats(struct net_device *dev,
> +					struct ethtool_stats *stats,
> +					u64 *data)
> +{
> +	struct virtnet_info *vi = netdev_priv(dev);
> +	unsigned int i, base;
> +	unsigned int start;
> +
> +	for (i = 0, base = 0; i < vi->max_queue_pairs; i++) {
> +		struct virtnet_tx_stats *tstats = &vi->sq[i].stats;
> +		struct virtnet_rx_stats *rstats = &vi->rq[i].stats;
> +
> +		do {
> +			start = u64_stats_fetch_begin_bh(&rstats->rx_syncp);
> +			data[base] = rstats->rx_packets;
> +			data[base+1] = rstats->rx_bytes;

nitpicking:
We normally has spaces around +, like this:
			data[base + 1] = rstats->rx_bytes;

> +		} while (u64_stats_fetch_retry_bh(&rstats->rx_syncp, start));
> +
> +		base += VIRTNET_RX_STATS_NUM;
> +
> +		do {
> +			start = u64_stats_fetch_begin_bh(&tstats->tx_syncp);
> +			data[base] = tstats->tx_packets;
> +			data[base+1]   = tstats->tx_bytes;

nitpicking:
Here, something strange happened to indentation.

> +		} while (u64_stats_fetch_retry_bh(&tstats->tx_syncp, start));
> +
> +		base += VIRTNET_TX_STATS_NUM;
> +	}
> +}
> +
> +
>  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,
> +	.get_strings = virtnet_get_stat_strings,
> +	.get_sset_count = virtnet_get_sset_count,
> +	.get_ethtool_stats = virtnet_get_ethtool_stats,
>  };
>  
>  #define MIN_MTU 68
> @@ -1531,14 +1636,11 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	vi->dev = dev;
>  	vi->vdev = vdev;
>  	vdev->priv = vi;
> -	vi->stats = alloc_percpu(struct virtnet_stats);
>  	err = -ENOMEM;
> -	if (vi->stats == NULL)
> -		goto free;
>  
>  	vi->vq_index = alloc_percpu(int);
>  	if (vi->vq_index == NULL)
> -		goto free_stats;
> +		goto free;
>  
>  	mutex_init(&vi->config_lock);
>  	vi->config_enable = true;
> @@ -1616,8 +1718,6 @@ free_vqs:
>  	virtnet_del_vqs(vi);
>  free_index:
>  	free_percpu(vi->vq_index);
> -free_stats:
> -	free_percpu(vi->stats);
>  free:
>  	free_netdev(dev);
>  	return err;
> @@ -1653,7 +1753,6 @@ static void virtnet_remove(struct virtio_device *vdev)
>  	flush_work(&vi->config_work);
>  
>  	free_percpu(vi->vq_index);
> -	free_percpu(vi->stats);
>  	free_netdev(vi->dev);
>  }

Thanks!

> -- 
> 1.7.1