/*
* Test null syscall performance
*
* Copyright (C) 2009-2015 Anton Blanchard, IBM
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#define NR_LOOPS 10000000
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
#include <sys/types.h>
#include <sys/time.h>
#include <signal.h>
static volatile int soak_done;
unsigned long long clock_frequency;
unsigned long long timebase_frequency;
double timebase_multiplier;
static inline unsigned long long mftb(void)
{
unsigned long low;
asm volatile("mftb %0" : "=r" (low));
return low;
}
static void sigalrm_handler(int unused)
{
soak_done = 1;
}
/*
* Use a timer instead of busy looping on clock_gettime() so we don't
* pollute profiles with glibc and VDSO hits.
*/
static void cpu_soak_usecs(unsigned long usecs)
{
struct itimerval val;
memset(&val, 0, sizeof(val));
val.it_value.tv_usec = usecs;
signal(SIGALRM, sigalrm_handler);
setitimer(ITIMER_REAL, &val, NULL);
while (1) {
if (soak_done)
break;
}
signal(SIGALRM, SIG_DFL);
}
/*
* This only works with recent kernels where cpufreq modifies
* /proc/cpuinfo dynamically.
*/
static void get_proc_frequency(void)
{
FILE *f;
char line[128];
char *p, *end;
unsigned long v;
double d;
char *override;
/* Try to get out of low power/low frequency mode */
cpu_soak_usecs(0.25 * 1000000);
f = fopen("/proc/cpuinfo", "r");
if (f == NULL)
return;
timebase_frequency = 0;
while (fgets(line, sizeof(line), f) != NULL) {
if (strncmp(line, "timebase", 8) == 0) {
p = strchr(line, ':');
if (p != NULL) {
v = strtoull(p + 1, &end, 0);
if (end != p + 1)
timebase_frequency = v;
}
}
if (((strncmp(line, "clock", 5) == 0) ||
(strncmp(line, "cpu MHz", 7) == 0))) {
p = strchr(line, ':');
if (p != NULL) {
d = strtod(p + 1, &end);
if (end != p + 1) {
/* Find fastest clock frequency */
if ((d * 1000000ULL) > clock_frequency)
clock_frequency = d * 1000000ULL;
}
}
}
}
fclose(f);
override = getenv("FREQUENCY");
if (override)
clock_frequency = strtoull(override, NULL, 10);
if (timebase_frequency)
timebase_multiplier = (double)clock_frequency
/ timebase_frequency;
else
timebase_multiplier = 1;
}
static void do_null_syscall(unsigned long nr)
{
unsigned long i;
for (i = 0; i < nr; i++)
getppid();
}
#define TIME(A, STR) \
int main(void)
{
unsigned long tb_start, tb_now;
struct timespec tv_start, tv_now;
unsigned long long elapsed_ns, elapsed_tb;
get_proc_frequency();
clock_gettime(CLOCK_MONOTONIC, &tv_start);
tb_start = mftb();
do_null_syscall(NR_LOOPS);
clock_gettime(CLOCK_MONOTONIC, &tv_now);
tb_now = mftb();
elapsed_ns = (tv_now.tv_sec - tv_start.tv_sec) * 1000000000ULL +
(tv_now.tv_nsec - tv_start.tv_nsec);
elapsed_tb = tb_now - tb_start;
printf("%10.2f ns %10.2f cycles\n", (float)elapsed_ns / NR_LOOPS,
(float)elapsed_tb * timebase_multiplier / NR_LOOPS);
return 0;
}
