tools/testing/selftests/powerpc/benchmarks/null_syscall.c

   1 /*
   2  * Test null syscall performance
   3  *
   4  * Copyright (C) 2009-2015 Anton Blanchard, IBM
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the License, or (at your option) any later version.
  10  */
  11
  12 #define NR_LOOPS 10000000
  13
  14 #include <string.h>
  15 #include <stdio.h>
  16 #include <stdlib.h>
  17 #include <unistd.h>
  18 #include <time.h>
  19 #include <sys/types.h>
  20 #include <sys/time.h>
  21 #include <signal.h>
  22
  23 static volatile int soak_done;
  24 unsigned long long clock_frequency;
  25 unsigned long long timebase_frequency;
  26 double timebase_multiplier;
  27
  28 static inline unsigned long long mftb(void)
  29 {
  30         unsigned long low;
  31
  32         asm volatile("mftb %0" : "=r" (low));
  33
  34         return low;
  35 }
  36
  37 static void sigalrm_handler(int unused)
  38 {
  39         soak_done = 1;
  40 }
  41
  42 /*
  43  * Use a timer instead of busy looping on clock_gettime() so we don't
  44  * pollute profiles with glibc and VDSO hits.
  45  */
  46 static void cpu_soak_usecs(unsigned long usecs)
  47 {
  48         struct itimerval val;
  49
  50         memset(&val, 0, sizeof(val));
  51         val.it_value.tv_usec = usecs;
  52
  53         signal(SIGALRM, sigalrm_handler);
  54         setitimer(ITIMER_REAL, &val, NULL);
  55
  56         while (1) {
  57                 if (soak_done)
  58                         break;
  59         }
  60
  61         signal(SIGALRM, SIG_DFL);
  62 }
  63
  64 /*
  65  * This only works with recent kernels where cpufreq modifies
  66  * /proc/cpuinfo dynamically.
  67  */
  68 static void get_proc_frequency(void)
  69 {
  70         FILE *f;
  71         char line[128];
  72         char *p, *end;
  73         unsigned long v;
  74         double d;
  75         char *override;
  76
  77         /* Try to get out of low power/low frequency mode */
  78         cpu_soak_usecs(0.25 * 1000000);
  79
  80         f = fopen("/proc/cpuinfo", "r");
  81         if (f == NULL)
  82                 return;
  83
  84         timebase_frequency = 0;
  85
  86         while (fgets(line, sizeof(line), f) != NULL) {
  87                 if (strncmp(line, "timebase", 8) == 0) {
  88                         p = strchr(line, ':');
  89                         if (p != NULL) {
  90                                 v = strtoull(p + 1, &end, 0);
  91                                 if (end != p + 1)
  92                                         timebase_frequency = v;
  93                         }
  94                 }
  95
  96                 if (((strncmp(line, "clock", 5) == 0) ||
  97                      (strncmp(line, "cpu MHz", 7) == 0))) {
  98                         p = strchr(line, ':');
  99                         if (p != NULL) {
 100                                 d = strtod(p + 1, &end);
 101                                 if (end != p + 1) {
 102                                         /* Find fastest clock frequency */
 103                                         if ((d * 1000000ULL) > clock_frequency)
 104                                                 clock_frequency = d * 1000000ULL;
 105                                 }
 106                         }
 107                 }
 108         }
 109
 110         fclose(f);
 111
 112         override = getenv("FREQUENCY");
 113         if (override)
 114                 clock_frequency = strtoull(override, NULL, 10);
 115
 116         if (timebase_frequency)
 117                 timebase_multiplier = (double)clock_frequency
 118                                         / timebase_frequency;
 119         else
 120                 timebase_multiplier = 1;
 121 }
 122
 123 static void do_null_syscall(unsigned long nr)
 124 {
 125         unsigned long i;
 126
 127         for (i = 0; i < nr; i++)
 128                 getppid();
 129 }
 130
 131 #define TIME(A, STR) \
 132
 133 int main(void)
 134 {
 135         unsigned long tb_start, tb_now;
 136         struct timespec tv_start, tv_now;
 137         unsigned long long elapsed_ns, elapsed_tb;
 138
 139         get_proc_frequency();
 140
 141         clock_gettime(CLOCK_MONOTONIC, &tv_start);
 142         tb_start = mftb();
 143
 144         do_null_syscall(NR_LOOPS);
 145
 146         clock_gettime(CLOCK_MONOTONIC, &tv_now);
 147         tb_now = mftb();
 148
 149         elapsed_ns = (tv_now.tv_sec - tv_start.tv_sec) * 1000000000ULL +
 150                         (tv_now.tv_nsec - tv_start.tv_nsec);
 151         elapsed_tb = tb_now - tb_start;
 152
 153         printf("%10.2f ns %10.2f cycles\n", (float)elapsed_ns / NR_LOOPS,
 154                         (float)elapsed_tb * timebase_multiplier / NR_LOOPS);
 155
 156         return 0;
 157 }