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