Subject: Re: [V2 RFC net-next PATCH 2/2] virtio_net: export more statistics through ethtool

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 6 Jun 2012 12:32:38 +0300

On Wed, Jun 06, 2012 at 03:52:17PM +0800, Jason Wang wrote:
> Satistics counters is useful for debugging and performance optimization, so this
> patch lets virtio_net driver collect following and export them to userspace
> through "ethtool -S":
> 
> - number of packets sent/received
> - number of bytes sent/received
> - number of callbacks for tx/rx
> - number of kick for tx/rx
> - number of bytes/packets queued for tx
> 
> As virtnet_stats were per-cpu, so both per-cpu and gloabl satistics were
> collected like:
> 
> NIC statistics:
>      tx_bytes[0]: 1731209929
>      tx_packets[0]: 60685
>      tx_kicks[0]: 63
>      tx_callbacks[0]: 73
>      tx_queued_bytes[0]: 1935749360
>      tx_queued_packets[0]: 80652
>      rx_bytes[0]: 2695648
>      rx_packets[0]: 40767
>      rx_kicks[0]: 1
>      rx_callbacks[0]: 2077
>      tx_bytes[1]: 9105588697
>      tx_packets[1]: 344150
>      tx_kicks[1]: 162
>      tx_callbacks[1]: 905
>      tx_queued_bytes[1]: 8901049412
>      tx_queued_packets[1]: 324184
>      rx_bytes[1]: 23679828
>      rx_packets[1]: 358770
>      rx_kicks[1]: 6
>      rx_callbacks[1]: 17717
>      tx_bytes: 10836798626
>      tx_packets: 404835
>      tx_kicks: 225
>      tx_callbacks: 978
>      tx_queued_bytes: 10836798772
>      tx_queued_packets: 404836
>      rx_bytes: 26375476
>      rx_packets: 399537
>      rx_kicks: 7
>      rx_callbacks: 19794
> 
> TODO:
> 
> - more statistics
> - calculate the pending bytes/pkts
> 
> Signed-off-by: Jason Wang <[email-masked]>
> 
> ---
> Changes from v1:
> 
> - style & typo fixs
> - convert the statistics fields to array
> - use unlikely()
> ---
>  drivers/net/virtio_net.c |  115 +++++++++++++++++++++++++++++++++++++++++++++-
>  1 files changed, 113 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 6e4aa6f..909a0a7 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -44,8 +44,14 @@ module_param(gso, bool, 0444);
>  enum virtnet_stats_type {
>  	VIRTNET_TX_BYTES,
>  	VIRTNET_TX_PACKETS,
> +	VIRTNET_TX_KICKS,
> +	VIRTNET_TX_CBS,
> +	VIRTNET_TX_Q_BYTES,
> +	VIRTNET_TX_Q_PACKETS,

What about counting the time we spend with queue
stopped and # of times we stop the queue?

>  	VIRTNET_RX_BYTES,
>  	VIRTNET_RX_PACKETS,
> +	VIRTNET_RX_KICKS,
> +	VIRTNET_RX_CBS,

What about a counter for oom on rx?

>  	VIRTNET_NUM_STATS,
>  };
>  
> @@ -54,6 +60,21 @@ struct virtnet_stats {
>  	u64 data[VIRTNET_NUM_STATS];
>  };
>  
> +static struct {
> +	char string[ETH_GSTRING_LEN];
> +} virtnet_stats_str_attr[] = {
> +	{ "tx_bytes" },
> +	{ "tx_packets" },
> +	{ "tx_kicks" },
> +	{ "tx_callbacks" },
> +	{ "tx_queued_bytes" },
> +	{ "tx_queued_packets" },
> +	{ "rx_bytes" },
> +	{ "rx_packets" },
> +	{ "rx_kicks" },
> +	{ "rx_callbacks" },
> +};
> +
>  struct virtnet_info {
>  	struct virtio_device *vdev;
>  	struct virtqueue *rvq, *svq, *cvq;
> @@ -146,6 +167,11 @@ static struct page *get_a_page(struct virtnet_info *vi, gfp_t gfp_mask)
>  static void skb_xmit_done(struct virtqueue *svq)
>  {
>  	struct virtnet_info *vi = svq->vdev->priv;
> +	struct virtnet_stats *stats = this_cpu_ptr(vi->stats);
> +
> +	u64_stats_update_begin(&stats->syncp);
> +	stats->data[VIRTNET_TX_CBS]++;
> +	u64_stats_update_end(&stats->syncp);
>  
>  	/* Suppress further interrupts. */
>  	virtqueue_disable_cb(svq);
> @@ -465,6 +491,7 @@ static bool try_fill_recv(struct virtnet_info *vi, gfp_t gfp)
>  {
>  	int err;
>  	bool oom;
> +	struct virtnet_stats *stats = this_cpu_ptr(vi->stats);
>  
>  	do {
>  		if (vi->mergeable_rx_bufs)
> @@ -481,13 +508,24 @@ static bool try_fill_recv(struct virtnet_info *vi, gfp_t gfp)
>  	} while (err > 0);
>  	if (unlikely(vi->num > vi->max))
>  		vi->max = vi->num;
> -	virtqueue_kick(vi->rvq);
> +	if (virtqueue_kick_prepare(vi->rvq)) {
> +		virtqueue_notify(vi->rvq);
> +		u64_stats_update_begin(&stats->syncp);
> +		stats->data[VIRTNET_RX_KICKS]++;
> +		u64_stats_update_end(&stats->syncp);
> +	}
>  	return !oom;
>  }
>  
>  static void skb_recv_done(struct virtqueue *rvq)
>  {
>  	struct virtnet_info *vi = rvq->vdev->priv;
> +	struct virtnet_stats *stats = this_cpu_ptr(vi->stats);
> +
> +	u64_stats_update_begin(&stats->syncp);
> +	stats->data[VIRTNET_RX_CBS]++;
> +	u64_stats_update_end(&stats->syncp);
> +

This data path so not entirely free.
I am guessing the overhead is not measureable but
did you check?

An alternative is to count when napi callbacks
are envoked. If we also count when weight was exceeded
we get almost the same result.

>  	/* Schedule NAPI, Suppress further interrupts if successful. */
>  	if (napi_schedule_prep(&vi->napi)) {
>  		virtqueue_disable_cb(rvq);
> @@ -630,7 +668,9 @@ static int xmit_skb(struct virtnet_info *vi, 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 virtnet_stats *stats = this_cpu_ptr(vi->stats);
>  	int capacity;
> +	bool kick;
>  
>  	/* Free up any pending old buffers before queueing new ones. */
>  	free_old_xmit_skbs(vi);
> @@ -655,7 +695,17 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
>  		kfree_skb(skb);
>  		return NETDEV_TX_OK;
>  	}
> -	virtqueue_kick(vi->svq);
> +
> +	kick = virtqueue_kick_prepare(vi->svq);
> +	if (unlikely(kick))
> +		virtqueue_notify(vi->svq);
> +
> +	u64_stats_update_begin(&stats->syncp);
> +	if (unlikely(kick))
> +		stats->data[VIRTNET_TX_KICKS]++;
> +	stats->data[VIRTNET_TX_Q_BYTES] += skb->len;
> +	stats->data[VIRTNET_TX_Q_PACKETS]++;
> +	u64_stats_update_end(&stats->syncp);
>  
>  	/* Don't wait up for transmitted skbs to be freed. */
>  	skb_orphan(skb);
> @@ -943,10 +993,71 @@ static void virtnet_get_drvinfo(struct net_device *dev,
>  
>  }
>  
> +static void virtnet_get_strings(struct net_device *dev, u32 stringset, u8 *buf)
> +{
> +	int i, cpu;
> +	switch (stringset) {
> +	case ETH_SS_STATS:
> +		for_each_possible_cpu(cpu)
> +			for (i = 0; i < VIRTNET_NUM_STATS; i++) {
> +				sprintf(buf, "%s[%u]",
> +					virtnet_stats_str_attr[i].string, cpu);
> +				buf += ETH_GSTRING_LEN;
> +			}
> +		for (i = 0; i < VIRTNET_NUM_STATS; i++) {
> +			memcpy(buf, virtnet_stats_str_attr[i].string,
> +				ETH_GSTRING_LEN);
> +			buf += ETH_GSTRING_LEN;
> +		}
> +		break;
> +	}
> +}
> +
> +static int virtnet_get_sset_count(struct net_device *dev, int sset)
> +{
> +	switch (sset) {
> +	case ETH_SS_STATS:
> +		return VIRTNET_NUM_STATS * (num_possible_cpus() + 1);
> +	default:
> +		return -EOPNOTSUPP;
> +	}
> +}
> +
> +static void virtnet_get_ethtool_stats(struct net_device *dev,
> +				      struct ethtool_stats *stats, u64 *buf)
> +{
> +	struct virtnet_info *vi = netdev_priv(dev);
> +	int cpu, i;
> +	unsigned int start;
> +	struct virtnet_stats sample, total;
> +
> +	memset(&total, 0, sizeof(total));
> +
> +	for_each_possible_cpu(cpu) {
> +		struct virtnet_stats *s = per_cpu_ptr(vi->stats, cpu);
> +		do {
> +			start = u64_stats_fetch_begin(&s->syncp);
> +			memcpy(&sample.data, &s->data,
> +			       sizeof(u64) * VIRTNET_NUM_STATS);
> +		} while (u64_stats_fetch_retry(&s->syncp, start));
> +
> +		for (i = 0; i < VIRTNET_NUM_STATS; i++) {
> +			*buf = sample.data[i];
> +			total.data[i] += sample.data[i];
> +			buf++;
> +		}
> +	}
> +
> +	memcpy(buf, &total.data, sizeof(u64) * VIRTNET_NUM_STATS);
> +}
> +
>  static const struct ethtool_ops virtnet_ethtool_ops = {
>  	.get_drvinfo = virtnet_get_drvinfo,
>  	.get_link = ethtool_op_get_link,
>  	.get_ringparam = virtnet_get_ringparam,
> +	.get_ethtool_stats = virtnet_get_ethtool_stats,
> +	.get_strings = virtnet_get_strings,
> +	.get_sset_count = virtnet_get_sset_count,
>  };
>  
>  #define MIN_MTU 68