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SubjectRE: [PATCH] virtio-net: Reporting traffic queue distribution statistics through ethtool
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Hi Michael,

Comments inline...

-----Original Message-----
From: Michael S. Tsirkin [mailto:mst@redhat.com]
Sent: Sunday, May 19, 2013 1:03 PM
To: Narasimhan, Sriram
Cc: rusty@rustcorp.com.au; virtualization@lists.linux-foundation.org; kvm@vger.kernel.org; netdev@vger.kernel.org; linux-kernel@vger.kernel.org; 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.


> 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

> -----Original Message-----
> From: Michael S. Tsirkin [mailto:mst@redhat.com]
> Sent: Sunday, May 19, 2013 4:28 AM
> To: Narasimhan, Sriram
> Cc: rusty@rustcorp.com.au; virtualization@lists.linux-foundation.org; kvm@vger.kernel.org; netdev@vger.kernel.org; linux-kernel@vger.kernel.org
> 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 <sriram.narasimhan@hp.com>
>
> 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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