LXR linux/tools/testing/selftests/powerpc/benchmarks/null

   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*
   3 * Test null syscall performance
   4 *
   5 * Copyright (C) 2009-2015 Anton Blanchard, IBM
   6 */
   7
   8#define NR_LOOPS 10000000
   9
  10#include <string.h>
  11#include <stdio.h>
  12#include <stdlib.h>
  13#include <unistd.h>
  14#include <time.h>
  15#include <sys/types.h>
  16#include <sys/time.h>
  17#include <sys/syscall.h>
  18#include <signal.h>
  19
  20static volatile int soak_done;
  21unsigned long long clock_frequency;
  22unsigned long long timebase_frequency;
  23double timebase_multiplier;
  24
  25static inline unsigned long mftb(void)
  26{
  27        unsigned long low;
  28
  29        asm volatile("mftb %0" : "=r" (low));
  30
  31        return low;
  32}
  33
  34static void sigalrm_handler(int unused)
  35{
  36        soak_done = 1;
  37}
  38
  39/*
  40 * Use a timer instead of busy looping on clock_gettime() so we don't
  41 * pollute profiles with glibc and VDSO hits.
  42 */
  43static void cpu_soak_usecs(unsigned long usecs)
  44{
  45        struct itimerval val;
  46
  47        memset(&val, 0, sizeof(val));
  48        val.it_value.tv_usec = usecs;
  49
  50        signal(SIGALRM, sigalrm_handler);
  51        setitimer(ITIMER_REAL, &val, NULL);
  52
  53        while (1) {
  54                if (soak_done)
  55                        break;
  56        }
  57
  58        signal(SIGALRM, SIG_DFL);
  59}
  60
  61/*
  62 * This only works with recent kernels where cpufreq modifies
  63 * /proc/cpuinfo dynamically.
  64 */
  65static void get_proc_frequency(void)
  66{
  67        FILE *f;
  68        char line[128];
  69        char *p, *end;
  70        unsigned long v;
  71        double d;
  72        char *override;
  73
  74        /* Try to get out of low power/low frequency mode */
  75        cpu_soak_usecs(0.25 * 1000000);
  76
  77        f = fopen("/proc/cpuinfo", "r");
  78        if (f == NULL)
  79                return;
  80
  81        timebase_frequency = 0;
  82
  83        while (fgets(line, sizeof(line), f) != NULL) {
  84                if (strncmp(line, "timebase", 8) == 0) {
  85                        p = strchr(line, ':');
  86                        if (p != NULL) {
  87                                v = strtoull(p + 1, &end, 0);
  88                                if (end != p + 1)
  89                                        timebase_frequency = v;
  90                        }
  91                }
  92
  93                if (((strncmp(line, "clock", 5) == 0) ||
  94                     (strncmp(line, "cpu MHz", 7) == 0))) {
  95                        p = strchr(line, ':');
  96                        if (p != NULL) {
  97                                d = strtod(p + 1, &end);
  98                                if (end != p + 1) {
  99                                        /* Find fastest clock frequency */
 100                                        if ((d * 1000000ULL) > clock_frequency)
 101                                                clock_frequency = d * 1000000ULL;
 102                                }
 103                        }
 104                }
 105        }
 106
 107        fclose(f);
 108
 109        override = getenv("FREQUENCY");
 110        if (override)
 111                clock_frequency = strtoull(override, NULL, 10);
 112
 113        if (timebase_frequency)
 114                timebase_multiplier = (double)clock_frequency
 115                                        / timebase_frequency;
 116        else
 117                timebase_multiplier = 1;
 118}
 119
 120static void do_null_syscall(unsigned long nr)
 121{
 122        unsigned long i;
 123
 124        for (i = 0; i < nr; i++)
 125                syscall(__NR_gettid);
 126}
 127
 128#define TIME(A, STR) \
 129
 130int main(void)
 131{
 132        unsigned long tb_start, tb_now;
 133        struct timespec tv_start, tv_now;
 134        unsigned long long elapsed_ns, elapsed_tb;
 135
 136        get_proc_frequency();
 137
 138        clock_gettime(CLOCK_MONOTONIC, &tv_start);
 139        tb_start = mftb();
 140
 141        do_null_syscall(NR_LOOPS);
 142
 143        clock_gettime(CLOCK_MONOTONIC, &tv_now);
 144        tb_now = mftb();
 145
 146        elapsed_ns = (tv_now.tv_sec - tv_start.tv_sec) * 1000000000ULL +
 147                        (tv_now.tv_nsec - tv_start.tv_nsec);
 148        elapsed_tb = tb_now - tb_start;
 149
 150        printf("%10.2f ns %10.2f cycles\n", (float)elapsed_ns / NR_LOOPS,
 151                        (float)elapsed_tb * timebase_multiplier / NR_LOOPS);
 152
 153        return 0;
 154}
 155