netdev - [PATCH v3 net-next 2/2] ibmvnic: Use ndo_get_stats64 to fix inaccurate SAR reporting

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Message-Id: <20250709184008.8473-3-mmc@linux.ibm.com>
Date: Wed,  9 Jul 2025 11:40:08 -0700
From: Mingming Cao <mmc@...ux.ibm.com>
To: netdev@...r.kernel.org
Cc: kuba@...nel.org, horms@...nel.org, bjking1@...ux.ibm.com,
        haren@...ux.ibm.com, ricklind@...ux.ibm.com, davemarq@...ux.ibm.com,
        mmc@...ux.ibm.com
Subject: [PATCH v3 net-next 2/2] ibmvnic: Use ndo_get_stats64 to fix inaccurate SAR reporting

VNIC testing on multi-core Power systems showed SAR stats drift
and packet rate inconsistencies under load.

Implements ndo_get_stats64 to provide safe aggregation of queue-level
atomic64 counters into rtnl_link_stats64 for use by tools like 'ip -s',
'ifconfig', and 'sar'. Switch to ndo_get_stats64 to align SAR reporting
with the standard kernel interface for retrieving netdev stats.

This removes redundant per-adapter stat updates, reduces overhead,
eliminates cacheline bouncing from hot path updates, and improves
the accuracy of reported packet rates.

Signed-off-by: Mingming Cao <mmc@...ux.ibm.com>
Reviewed by: Brian King <bjking1@...ux.ibm.com>
Reviewed by: Dave Marquardt <davemarq@...ux.ibm.com>
---
 drivers/net/ethernet/ibm/ibmvnic.c | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/ibm/ibmvnic.c b/drivers/net/ethernet/ibm/ibmvnic.c
index 79fdba4293a4..6dd7809b1bc7 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.c
+++ b/drivers/net/ethernet/ibm/ibmvnic.c
@@ -2312,8 +2312,6 @@ static void ibmvnic_tx_scrq_clean_buffer(struct ibmvnic_adapter *adapter,
 					  tx_pool->num_buffers - 1 :
 					  tx_pool->consumer_index - 1;
 		tx_buff = &tx_pool->tx_buff[index];
-		adapter->netdev->stats.tx_packets--;
-		adapter->netdev->stats.tx_bytes -= tx_buff->skb->len;
 		atomic64_dec(&adapter->tx_stats_buffers[queue_num].batched_packets);
 		if (atomic64_sub_return(tx_buff->skb->len,
 					&adapter->tx_stats_buffers[queue_num].bytes) < 0) {
@@ -2325,9 +2323,9 @@ static void ibmvnic_tx_scrq_clean_buffer(struct ibmvnic_adapter *adapter,
 				    atomic64_read(&adapter->tx_stats_buffers[queue_num].bytes),
 				    tx_buff->skb->len);
 		}
+		atomic64_inc(&adapter->tx_stats_buffers[queue_num].dropped_packets);
 		dev_kfree_skb_any(tx_buff->skb);
 		tx_buff->skb = NULL;
-		adapter->netdev->stats.tx_dropped++;
 	}
 
 	ind_bufp->index = 0;
@@ -2655,9 +2653,6 @@ static netdev_tx_t ibmvnic_xmit(struct sk_buff *skb, struct net_device *netdev)
 	}
 out:
 	rcu_read_unlock();
-	netdev->stats.tx_dropped += tx_dropped;
-	netdev->stats.tx_bytes += tx_bytes;
-	netdev->stats.tx_packets += tx_bpackets + tx_dpackets;
 	adapter->tx_send_failed += tx_send_failed;
 	adapter->tx_map_failed += tx_map_failed;
 	atomic64_add(tx_bpackets, &adapter->tx_stats_buffers[queue_num].batched_packets);
@@ -3460,6 +3455,25 @@ static int ibmvnic_reset(struct ibmvnic_adapter *adapter,
 	return -ret;
 }
 
+static void ibmvnic_get_stats64(struct net_device *netdev,
+				struct rtnl_link_stats64 *stats)
+{
+	struct ibmvnic_adapter *adapter = netdev_priv(netdev);
+	int i;
+
+	for (i = 0; i < adapter->req_rx_queues; i++) {
+		stats->rx_packets += atomic64_read(&adapter->rx_stats_buffers[i].packets);
+		stats->rx_bytes   += atomic64_read(&adapter->rx_stats_buffers[i].bytes);
+	}
+
+	for (i = 0; i < adapter->req_tx_queues; i++) {
+		stats->tx_packets += atomic64_read(&adapter->tx_stats_buffers[i].batched_packets);
+		stats->tx_packets += atomic64_read(&adapter->tx_stats_buffers[i].direct_packets);
+		stats->tx_bytes   += atomic64_read(&adapter->tx_stats_buffers[i].bytes);
+		stats->tx_dropped += atomic64_read(&adapter->tx_stats_buffers[i].dropped_packets);
+	}
+}
+
 static void ibmvnic_tx_timeout(struct net_device *dev, unsigned int txqueue)
 {
 	struct ibmvnic_adapter *adapter = netdev_priv(dev);
@@ -3575,8 +3589,6 @@ static int ibmvnic_poll(struct napi_struct *napi, int budget)
 
 		length = skb->len;
 		napi_gro_receive(napi, skb); /* send it up */
-		netdev->stats.rx_packets++;
-		netdev->stats.rx_bytes += length;
 		atomic64_inc(&adapter->rx_stats_buffers[scrq_num].packets);
 		atomic64_add(length, &adapter->rx_stats_buffers[scrq_num].bytes);
 		frames_processed++;
@@ -3686,6 +3698,7 @@ static const struct net_device_ops ibmvnic_netdev_ops = {
 	.ndo_set_rx_mode	= ibmvnic_set_multi,
 	.ndo_set_mac_address	= ibmvnic_set_mac,
 	.ndo_validate_addr	= eth_validate_addr,
+	.ndo_get_stats64	= ibmvnic_get_stats64,
 	.ndo_tx_timeout		= ibmvnic_tx_timeout,
 	.ndo_change_mtu		= ibmvnic_change_mtu,
 	.ndo_features_check     = ibmvnic_features_check,
-- 
2.39.3 (Apple Git-146)