155 lines · c
1// SPDX-License-Identifier: GPL-2.0-or-later2/*3 * Test null syscall performance4 *5 * Copyright (C) 2009-2015 Anton Blanchard, IBM6 */7 8#define NR_LOOPS 100000009 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't41 * 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 modifies63 * /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_frequency115 / timebase_frequency;116 else117 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