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From: Stephen Hemminger <stephen@networkplumber.org>
To: dev@dpdk.org
Cc: Stephen Hemminger <shemming@brocade.com>
Subject: [dpdk-dev] [PATCH v2 6/7] rte_sched: eliminate floating point in calculating byte clock
Date: Wed,  4 Feb 2015 22:14:00 -0800
Message-ID: <1423116841-19799-6-git-send-email-stephen@networkplumber.org> (raw)
In-Reply-To: <1423116841-19799-4-git-send-email-stephen@networkplumber.org>

From: Stephen Hemminger <shemming@brocade.com>

The old code was doing a floating point divide for each rte_dequeue()
which is very expensive. Change to using fixed point scaled math instead.
This improved performance from 5Gbit/sec to 10 Gbit/sec

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 lib/librte_sched/rte_sched.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/lib/librte_sched/rte_sched.c b/lib/librte_sched/rte_sched.c
index 55fbc14..3023457 100644
--- a/lib/librte_sched/rte_sched.c
+++ b/lib/librte_sched/rte_sched.c
@@ -102,6 +102,9 @@
 
 #define RTE_SCHED_BMP_POS_INVALID             UINT32_MAX
 
+/* For cycles_per_byte calculation */
+#define RTE_SCHED_TIME_SHIFT		      20
+
 struct rte_sched_subport {
 	/* Token bucket (TB) */
 	uint64_t tb_time; /* time of last update */
@@ -239,7 +242,7 @@ struct rte_sched_port {
 	uint64_t time_cpu_cycles;     /* Current CPU time measured in CPU cyles */
 	uint64_t time_cpu_bytes;      /* Current CPU time measured in bytes */
 	uint64_t time;                /* Current NIC TX time measured in bytes */
-	double cycles_per_byte;       /* CPU cycles per byte */
+	uint32_t cycles_per_byte;       /* CPU cycles per byte (scaled) */
 
 	/* Scheduling loop detection */
 	uint32_t pipe_loop;
@@ -657,7 +660,9 @@ rte_sched_port_config(struct rte_sched_port_params *params)
 	port->time_cpu_cycles = rte_get_tsc_cycles();
 	port->time_cpu_bytes = 0;
 	port->time = 0;
-	port->cycles_per_byte = ((double) rte_get_tsc_hz()) / ((double) params->rate);
+
+	port->cycles_per_byte = (rte_get_tsc_hz() << RTE_SCHED_TIME_SHIFT)
+		/ params->rate;
 
 	/* Scheduling loop detection */
 	port->pipe_loop = RTE_SCHED_PIPE_INVALID;
@@ -2156,11 +2161,12 @@ rte_sched_port_time_resync(struct rte_sched_port *port)
 {
 	uint64_t cycles = rte_get_tsc_cycles();
 	uint64_t cycles_diff = cycles - port->time_cpu_cycles;
-	double bytes_diff = ((double) cycles_diff) / port->cycles_per_byte;
+	uint64_t bytes_diff = (cycles_diff << RTE_SCHED_TIME_SHIFT)
+		/ port->cycles_per_byte;
 
 	/* Advance port time */
 	port->time_cpu_cycles = cycles;
-	port->time_cpu_bytes += (uint64_t) bytes_diff;
+	port->time_cpu_bytes += bytes_diff;
 	if (port->time < port->time_cpu_bytes) {
 		port->time = port->time_cpu_bytes;
 	}
-- 
2.1.4

  parent reply	other threads:[~2015-02-05  6:14 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-02-05  6:13 [dpdk-dev] [PATCH v2 4/7] rte_sched: don't clear statistics when read Stephen Hemminger
2015-02-05  6:13 ` [dpdk-dev] [PATCH v2 5/7] rte_sched: don't put tabs in log messages Stephen Hemminger
2015-02-20 18:33   ` Dumitrescu, Cristian
2015-02-05  6:14 ` Stephen Hemminger [this message]
2015-02-16 22:44   ` [dpdk-dev] [PATCH v2 6/7] rte_sched: eliminate floating point in calculating byte clock Dumitrescu, Cristian
2015-02-17 16:05     ` Stephen Hemminger
2015-02-05  6:14 ` [dpdk-dev] [PATCH v2 7/7] rte_sched: rearrange data structures Stephen Hemminger
2015-02-20 18:43   ` Dumitrescu, Cristian
2015-02-05 12:43 ` [dpdk-dev] [PATCH v2 4/7] rte_sched: don't clear statistics when read Neil Horman
2015-02-23 23:51   ` Thomas Monjalon
     [not found]   ` <fa17ab0c3bc041b88e18d3d76a255f13@HQ1WP-EXMB11.corp.brocade.com>
2015-02-24 19:18     ` Stephen Hemminger
2015-02-24 20:06       ` Thomas Monjalon
2015-02-25 17:29         ` Dumitrescu, Cristian
2015-03-10 13:55         ` Thomas Monjalon
2015-02-09 22:48 ` Dumitrescu, Cristian
2015-02-09 22:55   ` Stephen Hemminger
2015-02-20 18:32     ` Dumitrescu, Cristian
2015-02-20 19:52       ` Stephen Hemminger
2015-02-20 20:23         ` Dumitrescu, Cristian
2015-02-20 21:01           ` Thomas Monjalon
2015-02-20 21:28             ` Dumitrescu, Cristian
2015-02-21  1:53               ` Stephen Hemminger
2015-02-23 12:06                 ` Dumitrescu, Cristian
2015-02-09 23:46   ` Neil Horman

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