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