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 
20 static volatile int soak_done;
21 unsigned long long clock_frequency;
22 unsigned long long timebase_frequency;
23 double timebase_multiplier;
24 
mftb(void)25 static inline unsigned long mftb(void)
26 {
27 	unsigned long low;
28 
29 	asm volatile("mftb %0" : "=r" (low));
30 
31 	return low;
32 }
33 
sigalrm_handler(int unused)34 static 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  */
cpu_soak_usecs(unsigned long usecs)43 static 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  */
get_proc_frequency(void)65 static 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 
do_null_syscall(unsigned long nr)120 static 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 
main(void)130 int 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