[PATCH 07/12] net/pcap: avoid use of volatile

Stephen Hemminger
2026-01-06T18:34:00Z

Using volatile for statistics generates expensive atomic rmw
operations when not necessary.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
drivers/net/pcap/pcap_ethdev.c | 38 ++++++++++++++++++++++++++--------
1 file changed, 29 insertions(+), 9 deletions(-)

diff --git a/drivers/net/pcap/pcap_ethdev.c b/drivers/net/pcap/pcap_ethdev.c
index 1658685a28..175d6998f9 100644
--- a/drivers/net/pcap/pcap_ethdev.c
+++ b/drivers/net/pcap/pcap_ethdev.c
@@ -47,10 +47,10 @@ static uint64_t timestamp_rx_dynflag;
static int timestamp_dynfield_offset = -1;

struct queue_stat {
- volatile unsigned long pkts;
- volatile unsigned long bytes;
- volatile unsigned long err_pkts;
- volatile unsigned long rx_nombuf;
+ uint64_t pkts;
+ uint64_t bytes;
+ uint64_t err_pkts;
+ uint64_t rx_nombuf;
};

struct queue_missed_stat {
@@ -267,6 +267,9 @@ eth_pcap_rx_infinite(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
pcap_q->rx_stat.pkts += i;
pcap_q->rx_stat.bytes += rx_bytes;

+ /* ensure store operations of statistics are visible */
+ rte_atomic_thread_fence(rte_memory_order_release);
+
return i;
}

@@ -345,6 +348,9 @@ eth_pcap_rx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
pcap_q->rx_stat.pkts += num_rx;
pcap_q->rx_stat.bytes += rx_bytes;

+ /* ensure store operations of statistics are visible */
+ rte_atomic_thread_fence(rte_memory_order_release);
+
return num_rx;
}

@@ -440,6 +446,9 @@ eth_pcap_tx_dumper(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
dumper_q->tx_stat.bytes += tx_bytes;
dumper_q->tx_stat.err_pkts += nb_pkts - num_tx;

+ /* ensure store operations of statistics are visible */
+ rte_atomic_thread_fence(rte_memory_order_release);
+
return nb_pkts;
}

@@ -464,6 +473,9 @@ eth_tx_drop(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
tx_queue->tx_stat.pkts += nb_pkts;
tx_queue->tx_stat.bytes += tx_bytes;

+ /* ensure store operations of statistics are visible */
+ rte_atomic_thread_fence(rte_memory_order_release);
+
return nb_pkts;
}

@@ -515,6 +527,9 @@ eth_pcap_tx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
tx_queue->tx_stat.bytes += tx_bytes;
tx_queue->tx_stat.err_pkts += nb_pkts - num_tx;

+ /* ensure store operations of statistics are visible */
+ rte_atomic_thread_fence(rte_memory_order_release);
+
return nb_pkts;
}

@@ -821,13 +836,16 @@ eth_stats_get(struct rte_eth_dev *dev, struct rte_eth_stats *stats,
struct eth_queue_stats *qstats)
{
unsigned int i;
- unsigned long rx_packets_total = 0, rx_bytes_total = 0;
- unsigned long rx_missed_total = 0;
- unsigned long rx_nombuf_total = 0, rx_err_total = 0;
- unsigned long tx_packets_total = 0, tx_bytes_total = 0;
- unsigned long tx_packets_err_total = 0;
+ uint64_t rx_packets_total = 0, rx_bytes_total = 0;
+ uint64_t rx_missed_total = 0;
+ uint64_t rx_nombuf_total = 0, rx_err_total = 0;
+ uint64_t tx_packets_total = 0, tx_bytes_total = 0;
+ uint64_t tx_packets_err_total = 0;
const struct pmd_internals *internal = dev->data->dev_private;

+ /* ensure that current statistics are visible */
+ rte_atomic_thread_fence(rte_memory_order_acquire);
+
for (i = 0; i < RTE_ETHDEV_QUEUE_STAT_CNTRS &&
i < dev->data->nb_rx_queues; i++) {
if (qstats != NULL) {
@@ -884,6 +902,8 @@ eth_stats_reset(struct rte_eth_dev *dev)
internal->tx_queue[i].tx_stat.err_pkts = 0;
}

+ /* ensure store operations of statistics are visible */
+ rte_atomic_thread_fence(rte_memory_order_release);
return 0;
}

--
2.51.0