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

From: Jason Wang <[email-masked]>
Date: Mon, 20 May 2013 11:28:59 +0800

On 05/20/2013 06:56 AM, Narasimhan, Sriram wrote:
> Hi Michael,
>
> Comments inline...
>
> -----Original Message-----
> From: Michael S. Tsirkin [mailto:[email-masked]] 
> Sent: Sunday, May 19, 2013 1:03 PM
> To: Narasimhan, Sriram
> Cc: [email-masked]; [email-masked]; [email-masked]; [email-masked]; [email-masked]; Jason Wang
> Subject: Re: [PATCH] virtio-net: Reporting traffic queue distribution statistics through ethtool
>
> On Sun, May 19, 2013 at 04:09:48PM +0000, Narasimhan, Sriram wrote:
>> Hi Michael,
>>
>> I was getting all packets on the same inbound queue which
>> is why I added this support to virtio-net (and some more
>> instrumentation at tun as well).  But, it turned out to be
>> my misconfiguration - I did not enable IFF_MULTI_QUEUE on
>> the tap device, so the real_num_tx_queues on tap netdev was 
>> always 1 (no tx distribution at tap).
> Interesting that qemu didn't fail.
>
> [Sriram] void tun_set_real_num_tx_queues() does not return 
> the EINVAL return from netif_set_real_num_tx_queues() for 
> txq > dev->num_tx_queues (which would be the case if the
> tap device were not created with IFF_MULTI_QUEUE).  I think
> it would be better to fix the code to disable the new 
> queue and fail tun_attach() in this scenario.  If you 
> agree, I can go ahead and create a separate patch for that.
>    

But tun_attach() check the TUN_TAP_MQ flags before, so it should fail?
How was the tap created?
>> I am thinking about 
>> adding a -q option to tunctl to specify multi-queue flag on
>> the tap device.
> Absolutely.
>
> [Sriram] OK, let me do that.
>
>> Yes, number of exits will be most useful.  I will look into
>> adding the other statistics you mention.
>>
>> Sriram  
> Pls note you'll need to switch to virtqueue_kick_prepare
> to detect exits: virtqueue_kick doesn't let you know
> whether there was an exit.
>
> Also, it's best to make this a separate patch from the one
> adding per-queue stats.
>
> [Sriram] OK, I will cover only the per-queue statistics in
> this patch. Also, I will address the indentation/data 
> structure name points that you mentioned in your earlier
> email and send a new revision for this patch.
>
> Sriram

Better have some performance numbers to make sure nothing was slowed down.

Thanks
>
>> -----Original Message-----
>> From: Michael S. Tsirkin [mailto:[email-masked]] 
>> Sent: Sunday, May 19, 2013 4:28 AM
>> To: Narasimhan, Sriram
>> Cc: [email-masked]; [email-masked]; [email-masked]; [email-masked]; [email-masked]
>> Subject: Re: [PATCH] virtio-net: Reporting traffic queue distribution statistics through ethtool
>>
>> 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
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