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
19 static volatile int soak_done;
20 unsigned long long clock_frequency;
21 unsigned long long timebase_frequency;
22 double timebase_multiplier;
23
mftb(void)24 static inline unsigned long mftb(void)
25 {
26 unsigned long low;
27
28 asm volatile("mftb %0" : "=r" (low));
29
30 return low;
31 }
32
sigalrm_handler(int unused)33 static 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 */
cpu_soak_usecs(unsigned long usecs)42 static 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 */
get_proc_frequency(void)64 static 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
do_null_syscall(unsigned long nr)119 static 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
main(void)129 int 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