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.

---
 drivers/net/hyperv/hyperv_net.h |  9 +++++
 drivers/net/hyperv/netvsc_drv.c | 85 +++++++++++++++++++++++++++++++++++++----
 2 files changed, 86 insertions(+), 8 deletions(-)

index 41071d3..5a92b36 100644
@@ -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 */

1.8.5.2

From: Simon Xiao <[email protected]>
Date: Thu, 14 May 2015 01:00:25 -0700

Applied, thanks.