Subject: Re: [net-next RFC PATCH] virtio_net: collect satistics and export through ethtool

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 5 Jun 2012 13:10:37 +0300

On Tue, Jun 05, 2012 at 04:38:41PM +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 exposed
> like:
> 
> NIC statistics:
>      tx_bytes[0]: 2551
>      tx_packets[0]: 12
>      tx_kick[0]: 12
>      tx_callbacks[0]: 1
>      tx_queued_packets[0]: 12
>      tx_queued_bytes[0]: 3055
>      rx_bytes[0]: 0
>      rx_packets[0]: 0
>      rx_kick[0]: 0
>      rx_callbacks[0]: 0
>      tx_bytes[1]: 5575
>      tx_packets[1]: 37
>      tx_kick[1]: 38
>      tx_callbacks[1]: 0
>      tx_queued_packets[1]: 38
>      tx_queued_bytes[1]: 5217
>      rx_bytes[1]: 4175
>      rx_packets[1]: 25
>      rx_kick[1]: 1
>      rx_callbacks[1]: 16
>      tx_bytes: 8126
>      tx_packets: 49
>      tx_kick: 50
>      tx_callbacks: 1
>      tx_queued_packets: 50
>      tx_queued_bytes: 8272
>      rx_bytes: 4175
>      rx_packets: 25
>      rx_kick: 1
>      rx_callbacks: 16
> 
> TODO:
> 
> - more satistics
> - unitfy the ndo_get_stats64 and get_ethtool_stats
> - calculate the pending bytes/pkts
> 
> Signed-off-by: Jason Wang <[email-masked]>
> ---
>  drivers/net/virtio_net.c |  130 +++++++++++++++++++++++++++++++++++++++++++++-
>  1 files changed, 127 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 5214b1e..7ab0cc1 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -41,6 +41,10 @@ module_param(gso, bool, 0444);
>  #define VIRTNET_SEND_COMMAND_SG_MAX    2
>  #define VIRTNET_DRIVER_VERSION "1.0.0"
>  
> +#define VIRTNET_STAT_OFF(m) offsetof(struct virtnet_stats, m)
> +#define VIRTNET_STAT(stat, i) (*((u64 *)((char *)stat + \

What's going on? Why cast to char *?

> +			       virtnet_stats_str_attr[i].stat_offset)))

These are confusing unless you see what virtnet_stats_str_attr
is so please move them near that definition.

> +
>  struct virtnet_stats {
>  	struct u64_stats_sync syncp;
>  	u64 tx_bytes;
> @@ -48,8 +52,33 @@ struct virtnet_stats {
>  
>  	u64 rx_bytes;
>  	u64 rx_packets;
> +
> +	u64 tx_kick;
> +	u64 rx_kick;
> +	u64 tx_callbacks;
> +	u64 rx_callbacks;
> +	u64 tx_queued_packets;
> +	u64 tx_queued_bytes;
> +};

I have an idea (not a must): why don't we simply create an enum
enum virtnet_stats {
	VIRTNET_TX_KICK,
	VIRTNET_RX_KICK,
	....
	VIRTNET_MAX_STAT,
}

now stats can just do
	stats->data[VIRTNET_RX_KICK] instead of stats->rx_kick
which is not a big problem, but copying them in bulk
becomes straight-forward, no need for macros at all.

If we decide to do this, needs to be a separate patch,
then this one on top.

> +
> +static struct {

static const.

> +	char string[ETH_GSTRING_LEN];
> +	int stat_offset;
> +} virtnet_stats_str_attr[] = {
> +	{ "tx_bytes", VIRTNET_STAT_OFF(tx_bytes)},
> +	{ "tx_packets", VIRTNET_STAT_OFF(tx_packets)},
> +	{ "tx_kick", VIRTNET_STAT_OFF(tx_kick)},
> +	{ "tx_callbacks", VIRTNET_STAT_OFF(tx_callbacks)},
> +	{ "tx_queued_packets", VIRTNET_STAT_OFF(tx_queued_packets)},
> +	{ "tx_queued_bytes", VIRTNET_STAT_OFF(tx_queued_bytes)},
> +	{ "rx_bytes" , VIRTNET_STAT_OFF(rx_bytes)},
> +	{ "rx_packets", VIRTNET_STAT_OFF(rx_packets)},
> +	{ "rx_kick", VIRTNET_STAT_OFF(rx_kick)},
> +	{ "rx_callbacks", VIRTNET_STAT_OFF(rx_callbacks)},

VIRTNET_STAT_OFF does not save much here, but if you are after
saving characters then make the macro instanciate the string
as well.

>  };
>  
> +#define VIRTNET_NUM_STATS ARRAY_SIZE(virtnet_stats_str_attr)
> +

if you pass virtnet_stats_str_attr to VIRTNET_STAT macro,
then it's explicit and VIRTNET_NUM_STATS won't be needed either.

>  struct virtnet_info {
>  	struct virtio_device *vdev;
>  	struct virtqueue *rvq, *svq, *cvq;
> @@ -142,6 +171,11 @@ 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->tx_callbacks++;
> +	u64_stats_update_end(&stats->syncp);
>  
>  	/* Suppress further interrupts. */
>  	virtqueue_disable_cb(svq);
> @@ -461,6 +495,7 @@ 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)
> @@ -477,13 +512,24 @@ 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->rx_kick++;
> +		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->rx_callbacks++;
> +	u64_stats_update_end(&stats->syncp);
> +
>  	/* Schedule NAPI, Suppress further interrupts if successful. */
>  	if (napi_schedule_prep(&vi->napi)) {
>  		virtqueue_disable_cb(rvq);
> @@ -626,7 +672,9 @@ 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);
> @@ -651,7 +699,17 @@ 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 (kick)

probably
	 if (unlikely(kick))

> +		virtqueue_notify(vi->svq);
> +
> +	u64_stats_update_begin(&stats->syncp);
> +	if (kick)

this too

> +		stats->tx_kick++;
> +	stats->tx_queued_bytes += skb->len;
> +	stats->tx_queued_packets++;
> +	u64_stats_update_end(&stats->syncp);
>  
>  	/* Don't wait up for transmitted skbs to be freed. */
>  	skb_orphan(skb);
> @@ -926,7 +984,6 @@ static void virtnet_get_ringparam(struct net_device *dev,
>  
>  }
>  
> -
>  static void virtnet_get_drvinfo(struct net_device *dev,
>  				struct ethtool_drvinfo *info)
>  {
> @@ -939,10 +996,77 @@ 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_online_cpus() + 1);

This will allocate buffers for online cpus only, but the above
will fill them in for all possible cpus.
Will this overrun some buffer?

> +	default:
> +		return -EOPNOTSUPP;
> +	}
> +}
> +
> +static void virtnet_get_ethtool_stats(struct net_device *dev,
> +				struct ethtool_stats *stats, u64 *buf)

The coding style says
	Descendants are always substantially shorter than the parent and
	are placed substantially to the right.

you can't call it substantially to the right if it's to the left of
the opening '('  :), so please indent it aligning on the opening.

> +{
> +	struct virtnet_info *vi = netdev_priv(dev);
> +	int cpu, i;
> +	unsigned int start;
> +	struct virtnet_stats sample, total;
> +
> +	memset(&total, 0, sizeof(total));
> +	memset(&sample, 0, sizeof(sample));
> +
> +	for_each_possible_cpu(cpu) {
> +		struct virtnet_stats *stats = per_cpu_ptr(vi->stats, cpu);
> +		do {
> +			start = u64_stats_fetch_begin(&stats->syncp);
> +			for (i = 0; i < VIRTNET_NUM_STATS; i++) {
> +				VIRTNET_STAT(&sample, i) =
> +					VIRTNET_STAT(stats, i);

when you feel the need to break lines like this - don't :)
use an inline function instead.

> +

kill empty line here
> +			}

don't put {} around single statements pls.

> +		} while (u64_stats_fetch_retry(&stats->syncp, start));
> +		for (i = 0; i < VIRTNET_NUM_STATS; i++) {
> +			*buf = VIRTNET_STAT(&sample, i);
> +			VIRTNET_STAT(&total, i) += VIRTNET_STAT(stats, i);
> +			buf++;
> +		}
> +	}
> +
> +	for (i = 0; i < VIRTNET_NUM_STATS; i++) {
> +		*buf = VIRTNET_STAT(&total, i);
> +		buf++;
> +	}
> +}
> +
>  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