hv_netvsc: use per_cpu stats to calculate TX/RX data

Current code does not lock anything when calculating the TX and RX stats.
As a result, the RX and TX data reported by ifconfig are not accuracy in a
system with high network throughput and multiple CPUs (in my test,
RX/TX = 83% between 2 HyperV VM nodes which have 8 vCPUs and 40G Ethernet).

This patch fixed the above issue by using per_cpu stats.
netvsc_get_stats64() summarizes TX and RX data by iterating over all CPUs
to get their respective stats.

This v2 patch addressed David's comments on the cleanup path when
netdev_alloc_pcpu_stats() failed.
Signed-off-by: NSimon Xiao <sixiao@microsoft.com>
Reviewed-by: NK. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: NHaiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/hyperv/hyperv_net.h

@@ -611,6 +611,12 @@ struct multi_send_data {
 	u32 count; /* counter of batched packets */
 };
 
+struct netvsc_stats {
+	u64 packets;
+	u64 bytes;
+	struct u64_stats_sync s_sync;
+};
+
 /* The context of the netvsc device  */
 struct net_device_context {
 	/* point back to our device context */
@@ -618,6 +624,9 @@ struct net_device_context {
 	struct delayed_work dwork;
 	struct work_struct work;
 	u32 msg_enable; /* debug level */
+
+	struct netvsc_stats __percpu *tx_stats;
+	struct netvsc_stats __percpu *rx_stats;
 };
 
 /* Per netvsc device */

drivers/net/hyperv/netvsc_drv.c

@@ -391,7 +391,7 @@ static int netvsc_start_xmit(struct sk_buff *skb, struct net_device *net)
 	u32 skb_length;
 	u32 pkt_sz;
 	struct hv_page_buffer page_buf[MAX_PAGE_BUFFER_COUNT];
-
+	struct netvsc_stats *tx_stats = this_cpu_ptr(net_device_ctx->tx_stats);
 
 	/* We will atmost need two pages to describe the rndis
 	 * header. We can only transmit MAX_PAGE_BUFFER_COUNT number
@@ -580,8 +580,10 @@ static int netvsc_start_xmit(struct sk_buff *skb, struct net_device *net)
 
 drop:
 	if (ret == 0) {
-		net->stats.tx_bytes += skb_length;
-		net->stats.tx_packets++;
+		u64_stats_update_begin(&tx_stats->s_sync);
+		tx_stats->packets++;
+		tx_stats->bytes += skb_length;
+		u64_stats_update_end(&tx_stats->s_sync);
 	} else {
 		if (ret != -EAGAIN) {
 			dev_kfree_skb_any(skb);
@@ -644,13 +646,17 @@ int netvsc_recv_callback(struct hv_device *device_obj,
 				struct ndis_tcp_ip_checksum_info *csum_info)
 {
 	struct net_device *net;
+	struct net_device_context *net_device_ctx;
 	struct sk_buff *skb;
+	struct netvsc_stats *rx_stats;
 
 	net = ((struct netvsc_device *)hv_get_drvdata(device_obj))->ndev;
 	if (!net || net->reg_state != NETREG_REGISTERED) {
 		packet->status = NVSP_STAT_FAIL;
 		return 0;
 	}
+	net_device_ctx = netdev_priv(net);
+	rx_stats = this_cpu_ptr(net_device_ctx->rx_stats);
 
 	/* Allocate a skb - TODO direct I/O to pages? */
 	skb = netdev_alloc_skb_ip_align(net, packet->total_data_buflen);
@@ -686,8 +692,10 @@ int netvsc_recv_callback(struct hv_device *device_obj,
 	skb_record_rx_queue(skb, packet->channel->
 			    offermsg.offer.sub_channel_index);
 
-	net->stats.rx_packets++;
-	net->stats.rx_bytes += packet->total_data_buflen;
+	u64_stats_update_begin(&rx_stats->s_sync);
+	rx_stats->packets++;
+	rx_stats->bytes += packet->total_data_buflen;
+	u64_stats_update_end(&rx_stats->s_sync);
 
 	/*
 	 * Pass the skb back up. Network stack will deallocate the skb when it
@@ -753,6 +761,46 @@ static int netvsc_change_mtu(struct net_device *ndev, int mtu)
 	return 0;
 }
 
+static struct rtnl_link_stats64 *netvsc_get_stats64(struct net_device *net,
+						    struct rtnl_link_stats64 *t)
+{
+	struct net_device_context *ndev_ctx = netdev_priv(net);
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		struct netvsc_stats *tx_stats = per_cpu_ptr(ndev_ctx->tx_stats,
+							    cpu);
+		struct netvsc_stats *rx_stats = per_cpu_ptr(ndev_ctx->rx_stats,
+							    cpu);
+		u64 tx_packets, tx_bytes, rx_packets, rx_bytes;
+		unsigned int start;
+
+		do {
+			start = u64_stats_fetch_begin_irq(&tx_stats->s_sync);
+			tx_packets = tx_stats->packets;
+			tx_bytes = tx_stats->bytes;
+		} while (u64_stats_fetch_retry_irq(&tx_stats->s_sync, start));
+
+		do {
+			start = u64_stats_fetch_begin_irq(&rx_stats->s_sync);
+			rx_packets = rx_stats->packets;
+			rx_bytes = rx_stats->bytes;
+		} while (u64_stats_fetch_retry_irq(&rx_stats->s_sync, start));
+
+		t->tx_bytes	+= tx_bytes;
+		t->tx_packets	+= tx_packets;
+		t->rx_bytes	+= rx_bytes;
+		t->rx_packets	+= rx_packets;
+	}
+
+	t->tx_dropped	= net->stats.tx_dropped;
+	t->tx_errors	= net->stats.tx_dropped;
+
+	t->rx_dropped	= net->stats.rx_dropped;
+	t->rx_errors	= net->stats.rx_errors;
+
+	return t;
+}
 
 static int netvsc_set_mac_addr(struct net_device *ndev, void *p)
 {
@@ -804,6 +852,7 @@ static const struct net_device_ops device_ops = {
 	.ndo_validate_addr =		eth_validate_addr,
 	.ndo_set_mac_address =		netvsc_set_mac_addr,
 	.ndo_select_queue =		netvsc_select_queue,
+	.ndo_get_stats64 =		netvsc_get_stats64,
 #ifdef CONFIG_NET_POLL_CONTROLLER
 	.ndo_poll_controller =		netvsc_poll_controller,
 #endif
@@ -855,6 +904,14 @@ static void netvsc_link_change(struct work_struct *w)
 		netdev_notify_peers(net);
 }
 
+static void netvsc_free_netdev(struct net_device *netdev)
+{
+	struct net_device_context *net_device_ctx = netdev_priv(netdev);
+
+	free_percpu(net_device_ctx->tx_stats);
+	free_percpu(net_device_ctx->rx_stats);
+	free_netdev(netdev);
+}
 
 static int netvsc_probe(struct hv_device *dev,
 			const struct hv_vmbus_device_id *dev_id)
@@ -883,6 +940,18 @@ static int netvsc_probe(struct hv_device *dev,
 		netdev_dbg(net, "netvsc msg_enable: %d\n",
 			   net_device_ctx->msg_enable);
 
+	net_device_ctx->tx_stats = netdev_alloc_pcpu_stats(struct netvsc_stats);
+	if (!net_device_ctx->tx_stats) {
+		free_netdev(net);
+		return -ENOMEM;
+	}
+	net_device_ctx->rx_stats = netdev_alloc_pcpu_stats(struct netvsc_stats);
+	if (!net_device_ctx->rx_stats) {
+		free_percpu(net_device_ctx->tx_stats);
+		free_netdev(net);
+		return -ENOMEM;
+	}
+
 	hv_set_drvdata(dev, net);
 	INIT_DELAYED_WORK(&net_device_ctx->dwork, netvsc_link_change);
 	INIT_WORK(&net_device_ctx->work, do_set_multicast);
@@ -909,7 +978,7 @@ static int netvsc_probe(struct hv_device *dev,
 	ret = rndis_filter_device_add(dev, &device_info);
 	if (ret != 0) {
 		netdev_err(net, "unable to add netvsc device (ret %d)\n", ret);
-		free_netdev(net);
+		netvsc_free_netdev(net);
 		hv_set_drvdata(dev, NULL);
 		return ret;
 	}
@@ -923,7 +992,7 @@ static int netvsc_probe(struct hv_device *dev,
 	if (ret != 0) {
 		pr_err("Unable to register netdev.\n");
 		rndis_filter_device_remove(dev);
-		free_netdev(net);
+		netvsc_free_netdev(net);
 	} else {
 		schedule_delayed_work(&net_device_ctx->dwork, 0);
 	}
@@ -962,7 +1031,7 @@ static int netvsc_remove(struct hv_device *dev)
 	 */
 	rndis_filter_device_remove(dev);
 
-	free_netdev(net);
+	netvsc_free_netdev(net);
 	return 0;
 }