sched: eliminate floating point in calculating byte clock

[dpdk.git] / lib / librte_sched / rte_sched.c

diff --git a/lib/librte_sched/rte_sched.c b/lib/librte_sched/rte_sched.c
index 89007ad..1609ea8 100644 (file)
--- a/lib/librte_sched/rte_sched.c
+++ b/lib/librte_sched/rte_sched.c
@@ -47,6 +47,7 @@
 #include "rte_bitmap.h"
 #include "rte_sched_common.h"
 #include "rte_approx.h"
+#include "rte_reciprocal.h"
 
 #ifdef __INTEL_COMPILER
 #pragma warning(disable:2259) /* conversion may lose significant bits */
@@ -67,6 +68,11 @@
 #define RTE_SCHED_PIPE_INVALID                UINT32_MAX
 #define RTE_SCHED_BMP_POS_INVALID             UINT32_MAX
 
+/* Scaling for cycles_per_byte calculation
+ * Chosen so that minimum rate is 480 bit/sec
+ */
+#define RTE_SCHED_TIME_SHIFT                 8
+
 struct rte_sched_subport {
        /* Token bucket (TB) */
        uint64_t tb_time; /* time of last update */
@@ -220,7 +226,7 @@ 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 */
+       struct rte_reciprocal inv_cycles_per_byte; /* CPU cycles per byte */
 
        /* Scheduling loop detection */
        uint32_t pipe_loop;
@@ -615,7 +621,7 @@ struct rte_sched_port *
 rte_sched_port_config(struct rte_sched_port_params *params)
 {
        struct rte_sched_port *port = NULL;
-       uint32_t mem_size, bmp_mem_size, n_queues_per_port, i;
+       uint32_t mem_size, bmp_mem_size, n_queues_per_port, i, cycles_per_byte;
 
        /* Check user parameters. Determine the amount of memory to allocate */
        mem_size = rte_sched_port_get_memory_footprint(params);
@@ -666,7 +672,10 @@ 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);
+
+       cycles_per_byte = (rte_get_tsc_hz() << RTE_SCHED_TIME_SHIFT)
+               / params->rate;
+       port->inv_cycles_per_byte = rte_reciprocal_value(cycles_per_byte);
 
        /* Scheduling loop detection */
        port->pipe_loop = RTE_SCHED_PIPE_INVALID;
@@ -2093,11 +2102,15 @@ 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;
+
+       /* Compute elapsed time in bytes */
+       bytes_diff = rte_reciprocal_divide(cycles_diff << RTE_SCHED_TIME_SHIFT,
+                                          port->inv_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;