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From: Stephen Hemminger <stephen@networkplumber.org>
To: dev@dpdk.org
Cc: Stephen Hemminger <stephen@networkplumber.org>,
	Reshma Pattan <reshma.pattan@intel.com>
Subject: [PATCH v6 2/8] latencystats: handle fractional cycles per ns
Date: Wed, 29 May 2024 15:54:39 -0700	[thread overview]
Message-ID: <20240529225732.442539-3-stephen@networkplumber.org> (raw)
In-Reply-To: <20240529225732.442539-1-stephen@networkplumber.org>

The TSC frequency is not always an integral number of nanoseconds.
For examples, cycles per nanoseconds on my test system is 2.8.
Fix by using floating point where needed and calculate value once.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 lib/latencystats/rte_latencystats.c | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/lib/latencystats/rte_latencystats.c b/lib/latencystats/rte_latencystats.c
index 3fb8321484..c897df03c6 100644
--- a/lib/latencystats/rte_latencystats.c
+++ b/lib/latencystats/rte_latencystats.c
@@ -18,12 +18,7 @@
 /** Nano seconds per second */
 #define NS_PER_SEC 1E9
 
-/** Clock cycles per nano second */
-static uint64_t
-latencystat_cycles_per_ns(void)
-{
-	return rte_get_timer_hz() / NS_PER_SEC;
-}
+static double cycles_per_ns;
 
 RTE_LOG_REGISTER_DEFAULT(latencystat_logtype, INFO);
 #define RTE_LOGTYPE_LATENCY_STATS latencystat_logtype
@@ -89,8 +84,7 @@ rte_latencystats_update(void)
 	for (i = 0; i < NUM_LATENCY_STATS; i++) {
 		stats_ptr = RTE_PTR_ADD(glob_stats,
 				lat_stats_strings[i].offset);
-		values[i] = (uint64_t)floor((*stats_ptr)/
-				latencystat_cycles_per_ns());
+		values[i] = floor(*stats_ptr / cycles_per_ns);
 	}
 
 	ret = rte_metrics_update_values(RTE_METRICS_GLOBAL,
@@ -112,8 +106,7 @@ rte_latencystats_fill_values(struct rte_metric_value *values)
 		stats_ptr = RTE_PTR_ADD(glob_stats,
 				lat_stats_strings[i].offset);
 		values[i].key = i;
-		values[i].value = (uint64_t)floor((*stats_ptr)/
-						latencystat_cycles_per_ns());
+		values[i].value = floor(*stats_ptr / cycles_per_ns);
 	}
 }
 
@@ -235,9 +228,11 @@ rte_latencystats_init(uint64_t app_samp_intvl,
 		return -ENOMEM;
 	}
 
+	cycles_per_ns = (double)rte_get_tsc_hz() / NS_PER_SEC;
+
 	glob_stats = mz->addr;
 	rte_spinlock_init(&glob_stats->lock);
-	samp_intvl = app_samp_intvl * latencystat_cycles_per_ns();
+	samp_intvl = (uint64_t)(app_samp_intvl * cycles_per_ns);
 
 	/** Register latency stats with stats library */
 	for (i = 0; i < NUM_LATENCY_STATS; i++)
-- 
2.43.0


  parent reply	other threads:[~2024-05-29 22:57 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-04-08 19:50 [RFC] latencystats: performance overhaul Stephen Hemminger
2024-04-08 21:26 ` [PATCH v2] " Stephen Hemminger
2024-04-19 17:28 ` [PATCH v4 0/6] latencystats: cleanup Stephen Hemminger
2024-04-19 17:28   ` [PATCH v4 1/6] latencystats: replace use of VLA Stephen Hemminger
2024-04-19 17:28   ` [PATCH v4 2/6] latencystats: handle fractional cycles per ns Stephen Hemminger
2024-04-19 17:28   ` [PATCH v4 3/6] latencystats: do not use floating point Stephen Hemminger
2024-04-19 18:49     ` Morten Brørup
2024-04-19 22:45       ` Stephen Hemminger
2024-04-20  7:31         ` Morten Brørup
2024-04-19 17:28   ` [PATCH v4 4/6] latencystats: fix log messages Stephen Hemminger
2024-04-19 17:28   ` [PATCH v4 5/6] latencystats: update include files Stephen Hemminger
2024-04-19 17:28   ` [PATCH v4 6/6] latencystats: fix for pedantic warnings Stephen Hemminger
2024-04-22 15:21 ` [PATCH v5 0/9] latencystats: improve algorithms and tests Stephen Hemminger
2024-04-22 15:21   ` [PATCH v5 1/9] latencystats: replace use of VLA Stephen Hemminger
2024-04-22 15:21   ` [PATCH v5 2/9] latencystats: handle fractional cycles per ns Stephen Hemminger
2024-04-22 15:21   ` [PATCH v5 3/9] latencystats: do not use floating point Stephen Hemminger
2024-04-22 15:21   ` [PATCH v5 4/9] latencystats: fix log messages Stephen Hemminger
2024-04-22 15:21   ` [PATCH v5 5/9] latencystats: update include files Stephen Hemminger
2024-04-22 15:21   ` [PATCH v5 6/9] latencystats: enforce that unused callback function is NULL Stephen Hemminger
2024-04-22 15:21   ` [PATCH v5 7/9] latencystats: add metric for number of samples Stephen Hemminger
2024-04-22 15:21   ` [PATCH v5 8/9] test: use initialization in latencystats test Stephen Hemminger
2024-04-22 15:21   ` [PATCH v5 9/9] test: add more latencystats tests Stephen Hemminger
2024-05-29 22:54 ` [PATCH v6 0/8] latencystats: improvements to algorithm and test Stephen Hemminger
2024-05-29 22:54   ` [PATCH v6 1/8] latencystats: replace use of VLA Stephen Hemminger
2024-05-29 22:54   ` Stephen Hemminger [this message]
2024-05-29 22:54   ` [PATCH v6 3/8] latencystats: do not use floating point Stephen Hemminger
2024-05-29 22:54   ` [PATCH v6 4/8] latencystats: fix log messages Stephen Hemminger
2024-05-29 22:54   ` [PATCH v6 5/8] latencystats: update include files Stephen Hemminger
2024-05-29 22:54   ` [PATCH v6 6/8] latencystats: enforce that unused callback function is NULL Stephen Hemminger
2024-05-29 22:54   ` [PATCH v6 7/8] latencystats: add metric for number of samples Stephen Hemminger
2024-05-29 22:54   ` [PATCH v6 8/8] test: update to latencystats tests Stephen Hemminger
2024-07-04 15:21   ` [PATCH v6 0/8] latencystats: improvements to algorithm and test David Marchand

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