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

   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
  20 static volatile int soak_done;
  21 unsigned long long clock_frequency;
  22 unsigned long long timebase_frequency;
  23 double timebase_multiplier;
  24
  25 static inline unsigned long mftb(void)
  26 {
  27         unsigned long low;
  28
  29         asm volatile("mftb %0" : "=r" (low));
  30
  31         return low;
  32 }
  33
  34 static 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  */
  43 static 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  */
  65 static 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
 120 static 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
 130 int 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 }