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 
28 static inline unsigned long mftb(void)
29 {
30 	unsigned long low;
31 
32 	asm volatile("mftb %0" : "=r" (low));
33 
34 	return low;
35 }
36 
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  */
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  */
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 
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 
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