vlan: Precise RX stats accounting

With multi queue devices, its possible that several cpus call
vlan RX routines simultaneously for the same vlan device.

We update RX stats counter without any locking, so we can
get slightly wrong counters.

One possible fix is to use percpu counters, to get precise
accounting and also get guarantee of no cache line ping pongs
between cpus.

Note: this adds 16 bytes (32 bytes on 64bit arches) of percpu
data per vlan device.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 41 insertions, 6 deletions

diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c
index 915965942139..de0dc6bacbe8 100644
--- a/net/8021q/vlan_dev.c
+++ b/net/8021q/vlan_dev.c
@@ -140,7 +140,7 @@ int vlan_skb_recv(struct sk_buff *skb, struct net_device *dev,
 		  struct packet_type *ptype, struct net_device *orig_dev)
 {
 	struct vlan_hdr *vhdr;
-	struct net_device_stats *stats;
+	struct vlan_rx_stats *rx_stats;
 	u16 vlan_id;
 	u16 vlan_tci;
 
@@ -163,9 +163,10 @@ int vlan_skb_recv(struct sk_buff *skb, struct net_device *dev,
 		goto err_unlock;
 	}
 
-	stats = &skb->dev->stats;
-	stats->rx_packets++;
-	stats->rx_bytes += skb->len;
+	rx_stats = per_cpu_ptr(vlan_dev_info(dev)->vlan_rx_stats,
+			       smp_processor_id());
+	rx_stats->rx_packets++;
+	rx_stats->rx_bytes += skb->len;
 
 	skb_pull_rcsum(skb, VLAN_HLEN);
 
@@ -180,7 +181,7 @@ int vlan_skb_recv(struct sk_buff *skb, struct net_device *dev,
 		break;
 
 	case PACKET_MULTICAST:
-		stats->multicast++;
+		rx_stats->multicast++;
 		break;
 
 	case PACKET_OTHERHOST:
@@ -200,7 +201,7 @@ int vlan_skb_recv(struct sk_buff *skb, struct net_device *dev,
 
 	skb = vlan_check_reorder_header(skb);
 	if (!skb) {
-		stats->rx_errors++;
+		rx_stats->rx_errors++;
 		goto err_unlock;
 	}
 
@@ -731,6 +732,11 @@ static int vlan_dev_init(struct net_device *dev)
 		subclass = 1;
 
 	vlan_dev_set_lockdep_class(dev, subclass);
+
+	vlan_dev_info(dev)->vlan_rx_stats = alloc_percpu(struct vlan_rx_stats);
+	if (!vlan_dev_info(dev)->vlan_rx_stats)
+		return -ENOMEM;
+
 	return 0;
 }
 
@@ -740,6 +746,8 @@ static void vlan_dev_uninit(struct net_device *dev)
 	struct vlan_dev_info *vlan = vlan_dev_info(dev);
 	int i;
 
+	free_percpu(vlan->vlan_rx_stats);
+	vlan->vlan_rx_stats = NULL;
 	for (i = 0; i < ARRAY_SIZE(vlan->egress_priority_map); i++) {
 		while ((pm = vlan->egress_priority_map[i]) != NULL) {
 			vlan->egress_priority_map[i] = pm->next;
@@ -775,6 +783,31 @@ static u32 vlan_ethtool_get_flags(struct net_device *dev)
 	return dev_ethtool_get_flags(vlan->real_dev);
 }
 
+static struct net_device_stats *vlan_dev_get_stats(struct net_device *dev)
+{
+	struct net_device_stats *stats = &dev->stats;
+
+	dev_txq_stats_fold(dev, stats);
+
+	if (vlan_dev_info(dev)->vlan_rx_stats) {
+		struct vlan_rx_stats *p, rx = {0};
+		int i;
+
+		for_each_possible_cpu(i) {
+			p = per_cpu_ptr(vlan_dev_info(dev)->vlan_rx_stats, i);
+			rx.rx_packets += p->rx_packets;
+			rx.rx_bytes   += p->rx_bytes;
+			rx.rx_errors  += p->rx_errors;
+			rx.multicast  += p->multicast;
+		}
+		stats->rx_packets = rx.rx_packets;
+		stats->rx_bytes   = rx.rx_bytes;
+		stats->rx_errors  = rx.rx_errors;
+		stats->multicast  = rx.multicast;
+	}
+	return stats;
+}
+
 static const struct ethtool_ops vlan_ethtool_ops = {
 	.get_settings	        = vlan_ethtool_get_settings,
 	.get_drvinfo	        = vlan_ethtool_get_drvinfo,
@@ -797,6 +830,7 @@ static const struct net_device_ops vlan_netdev_ops = {
 	.ndo_change_rx_flags	= vlan_dev_change_rx_flags,
 	.ndo_do_ioctl		= vlan_dev_ioctl,
 	.ndo_neigh_setup	= vlan_dev_neigh_setup,
+	.ndo_get_stats		= vlan_dev_get_stats,
 #if defined(CONFIG_FCOE) || defined(CONFIG_FCOE_MODULE)
 	.ndo_fcoe_ddp_setup	= vlan_dev_fcoe_ddp_setup,
 	.ndo_fcoe_ddp_done	= vlan_dev_fcoe_ddp_done,
@@ -820,6 +854,7 @@ static const struct net_device_ops vlan_netdev_accel_ops = {
 	.ndo_change_rx_flags	= vlan_dev_change_rx_flags,
 	.ndo_do_ioctl		= vlan_dev_ioctl,
 	.ndo_neigh_setup	= vlan_dev_neigh_setup,
+	.ndo_get_stats		= vlan_dev_get_stats,
 #if defined(CONFIG_FCOE) || defined(CONFIG_FCOE_MODULE)
 	.ndo_fcoe_ddp_setup	= vlan_dev_fcoe_ddp_setup,
 	.ndo_fcoe_ddp_done	= vlan_dev_fcoe_ddp_done,