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154 lines · 2.9 KiB

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}