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
mftb(void)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
sigalrm_handler(int unused)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 */
cpu_soak_usecs(unsigned long usecs)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 */
get_proc_frequency(void)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
do_null_syscall(unsigned long nr)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
main(void)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 }
158