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