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}
155