[PATCH 08/12] net/pcap: optimize calculation of receive timestamp

[Stephen Hemminger]

Avoid doing slow instructions in receive path when calculating
timestamp. Give all packets in the same rx burst the same timestamp.

Signed-off-by: Stephen Hemminger <stephen at networkplumber.org>
---
 drivers/net/pcap/pcap_ethdev.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/drivers/net/pcap/pcap_ethdev.c b/drivers/net/pcap/pcap_ethdev.c
index 175d6998f9..e283fb3787 100644
--- a/drivers/net/pcap/pcap_ethdev.c
+++ b/drivers/net/pcap/pcap_ethdev.c
@@ -20,6 +20,7 @@
 #include <bus_vdev_driver.h>
 #include <rte_os_shim.h>
 #include <rte_time.h>
+#include <rte_reciprocal.h>
 
 #include "pcap_osdep.h"
 
@@ -41,7 +42,7 @@
 
 static struct timespec start_time;
 static uint64_t start_cycles;
-static uint64_t hz;
+static struct rte_reciprocal_u64 hz_inv;
 
 static uint64_t timestamp_rx_dynflag;
 static int timestamp_dynfield_offset = -1;
@@ -362,8 +363,6 @@ eth_null_rx(void *queue __rte_unused,
 	return 0;
 }
 
-#define NSEC_PER_SEC	1000000000L
-
 /*
  * This function stores nanoseconds in `tv_usec` field of `struct timeval`,
  * because `ts` goes directly to nanosecond-precision dump.
@@ -374,8 +373,10 @@ calculate_timestamp(struct timeval *ts) {
 	struct timespec cur_time;
 
 	cycles = rte_get_timer_cycles() - start_cycles;
-	cur_time.tv_sec = cycles / hz;
-	cur_time.tv_nsec = (cycles % hz) * NSEC_PER_SEC / hz;
+	cur_time.tv_sec = rte_reciprocal_divide_u64(cycles, &hz_inv);
+	/* compute remainder */
+	cycles -= cur_time.tv_sec * rte_get_timer_hz();
+	cur_time.tv_nsec = rte_reciprocal_divide_u64(cycles * NS_PER_S, &hz_inv);
 
 	ts->tv_sec = start_time.tv_sec + cur_time.tv_sec;
 	ts->tv_usec = start_time.tv_nsec + cur_time.tv_nsec;
@@ -394,6 +395,7 @@ eth_pcap_tx_dumper(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 	unsigned int i;
 	struct pmd_process_private *pp;
 	struct pcap_tx_queue *dumper_q = queue;
+	struct pcap_pkthdr header;
 	uint16_t num_tx = 0;
 	uint32_t tx_bytes = 0;
 	pcap_dumper_t *dumper;
@@ -406,13 +408,14 @@ eth_pcap_tx_dumper(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 	if (unlikely(dumper == NULL || nb_pkts == 0))
 		return 0;
 
-	/* writes the nb_pkts packets to the previously opened pcap file
-	 * dumper */
+	/* all packets in burst have same timestamp */
+	calculate_timestamp(&header.ts);
+
+	/* writes the nb_pkts packets to the previously opened pcap file dumper */
 	for (i = 0; i < nb_pkts; i++) {
 		struct rte_mbuf *mbuf = bufs[i];
 		size_t len = rte_pktmbuf_pkt_len(mbuf);
 		uint8_t temp_data[RTE_ETH_PCAP_SNAPLEN];
-		struct pcap_pkthdr header;
 
 		if (unlikely(len > mtu))
 			continue;
@@ -420,7 +423,6 @@ eth_pcap_tx_dumper(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 		if ((mbuf->ol_flags & RTE_MBUF_F_TX_VLAN) && rte_vlan_insert(&mbuf))
 			continue;
 
-		calculate_timestamp(&header.ts);
 		header.len = len;
 		header.caplen = len;
 
@@ -1530,7 +1532,8 @@ pmd_pcap_probe(struct rte_vdev_device *dev)
 
 	timespec_get(&start_time, TIME_UTC);
 	start_cycles = rte_get_timer_cycles();
-	hz = rte_get_timer_hz();
+
+	hz_inv = rte_reciprocal_value_u64(rte_get_timer_hz());
 
 	if (rte_eal_process_type() == RTE_PROC_SECONDARY) {
 		eth_dev = rte_eth_dev_attach_secondary(name);
-- 
2.51.0