[RFC] net/af_packet: make stats reset reliable

[Ferruh Yigit <ferruh.yigit@amd.com>]

For stats reset, use an offset instead of zeroing out actual stats values,
get_stats() displays diff between stats and offset.
This way stats only updated in datapath and offset only updated in stats
reset function. This makes stats reset function more reliable.

As stats only written by single thread, we can remove 'volatile' qualifier
which should improve the performance in datapath.

Signed-off-by: Ferruh Yigit <ferruh.yigit@amd.com>
---
Cc: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Morten Brørup <mb@smartsharesystems.com>

This update triggered by mail list discussion [1].

[1]
https://inbox.dpdk.org/dev/3b2cf48e-2293-4226-b6cd-5f4dd3969f99@lysator.liu.se/
---
 drivers/net/af_packet/rte_eth_af_packet.c | 69 +++++++++++++++--------
 1 file changed, 44 insertions(+), 25 deletions(-)

diff --git a/drivers/net/af_packet/rte_eth_af_packet.c b/drivers/net/af_packet/rte_eth_af_packet.c
index 397a32db5886..2061cdab4997 100644
--- a/drivers/net/af_packet/rte_eth_af_packet.c
+++ b/drivers/net/af_packet/rte_eth_af_packet.c
@@ -51,8 +51,10 @@ struct pkt_rx_queue {
 	uint16_t in_port;
 	uint8_t vlan_strip;
 
-	volatile unsigned long rx_pkts;
-	volatile unsigned long rx_bytes;
+	uint64_t rx_pkts;
+	uint64_t rx_bytes;
+	uint64_t rx_pkts_offset;
+	uint64_t rx_bytes_offset;
 };
 
 struct pkt_tx_queue {
@@ -64,9 +66,12 @@ struct pkt_tx_queue {
 	unsigned int framecount;
 	unsigned int framenum;
 
-	volatile unsigned long tx_pkts;
-	volatile unsigned long err_pkts;
-	volatile unsigned long tx_bytes;
+	uint64_t tx_pkts;
+	uint64_t err_pkts;
+	uint64_t tx_bytes;
+	uint64_t tx_pkts_offset;
+	uint64_t err_pkts_offset;
+	uint64_t tx_bytes_offset;
 };
 
 struct pmd_internals {
@@ -385,8 +390,18 @@ eth_dev_info(struct rte_eth_dev *dev, struct rte_eth_dev_info *dev_info)
 	return 0;
 }
 
+
+static uint64_t
+stats_get_diff(uint64_t stats, uint64_t offset)
+{
+	if (stats >= offset)
+		return stats - offset;
+	/* unlikely wraparound case */
+	return UINT64_MAX + stats - offset;
+}
+
 static int
-eth_stats_get(struct rte_eth_dev *dev, struct rte_eth_stats *igb_stats)
+eth_stats_get(struct rte_eth_dev *dev, struct rte_eth_stats *stats)
 {
 	unsigned i, imax;
 	unsigned long rx_total = 0, tx_total = 0, tx_err_total = 0;
@@ -396,27 +411,29 @@ eth_stats_get(struct rte_eth_dev *dev, struct rte_eth_stats *igb_stats)
 	imax = (internal->nb_queues < RTE_ETHDEV_QUEUE_STAT_CNTRS ?
 	        internal->nb_queues : RTE_ETHDEV_QUEUE_STAT_CNTRS);
 	for (i = 0; i < imax; i++) {
-		igb_stats->q_ipackets[i] = internal->rx_queue[i].rx_pkts;
-		igb_stats->q_ibytes[i] = internal->rx_queue[i].rx_bytes;
-		rx_total += igb_stats->q_ipackets[i];
-		rx_bytes_total += igb_stats->q_ibytes[i];
+		struct pkt_rx_queue *rxq = &internal->rx_queue[i];
+		stats->q_ipackets[i] = stats_get_diff(rxq->rx_pkts, rxq->rx_pkts_offset);
+		stats->q_ibytes[i] = stats_get_diff(rxq->rx_bytes, rxq->rx_bytes_offset);
+		rx_total += stats->q_ipackets[i];
+		rx_bytes_total += stats->q_ibytes[i];
 	}
 
 	imax = (internal->nb_queues < RTE_ETHDEV_QUEUE_STAT_CNTRS ?
 	        internal->nb_queues : RTE_ETHDEV_QUEUE_STAT_CNTRS);
 	for (i = 0; i < imax; i++) {
-		igb_stats->q_opackets[i] = internal->tx_queue[i].tx_pkts;
-		igb_stats->q_obytes[i] = internal->tx_queue[i].tx_bytes;
-		tx_total += igb_stats->q_opackets[i];
-		tx_err_total += internal->tx_queue[i].err_pkts;
-		tx_bytes_total += igb_stats->q_obytes[i];
+		struct pkt_tx_queue *txq = &internal->tx_queue[i];
+		stats->q_opackets[i] = stats_get_diff(txq->tx_pkts, txq->tx_pkts_offset);
+		stats->q_obytes[i] = stats_get_diff(txq->tx_bytes, txq->tx_bytes_offset);
+		tx_total += stats->q_opackets[i];
+		tx_err_total += stats_get_diff(txq->err_pkts, txq->err_pkts_offset);
+		tx_bytes_total += stats->q_obytes[i];
 	}
 
-	igb_stats->ipackets = rx_total;
-	igb_stats->ibytes = rx_bytes_total;
-	igb_stats->opackets = tx_total;
-	igb_stats->oerrors = tx_err_total;
-	igb_stats->obytes = tx_bytes_total;
+	stats->ipackets = rx_total;
+	stats->ibytes = rx_bytes_total;
+	stats->opackets = tx_total;
+	stats->oerrors = tx_err_total;
+	stats->obytes = tx_bytes_total;
 	return 0;
 }
 
@@ -427,14 +444,16 @@ eth_stats_reset(struct rte_eth_dev *dev)
 	struct pmd_internals *internal = dev->data->dev_private;
 
 	for (i = 0; i < internal->nb_queues; i++) {
-		internal->rx_queue[i].rx_pkts = 0;
-		internal->rx_queue[i].rx_bytes = 0;
+		struct pkt_rx_queue *rxq = &internal->rx_queue[i];
+		rxq->rx_pkts_offset = rxq->rx_pkts;
+		rxq->rx_bytes_offset = rxq->rx_bytes;
 	}
 
 	for (i = 0; i < internal->nb_queues; i++) {
-		internal->tx_queue[i].tx_pkts = 0;
-		internal->tx_queue[i].err_pkts = 0;
-		internal->tx_queue[i].tx_bytes = 0;
+		struct pkt_tx_queue *txq = &internal->tx_queue[i];
+		txq->tx_pkts_offset = txq->tx_pkts;
+		txq->err_pkts_offset = txq->err_pkts;
+		txq->tx_bytes_offset = txq->tx_bytes;
 	}
 
 	return 0;
-- 
2.34.1