1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright 2013, Michael Ellerman, IBM Corp.
4 */
5
6#define _GNU_SOURCE
7
8#include <stdio.h>
9#include <stdbool.h>
10#include <string.h>
11#include <sys/prctl.h>
12
13#include "event.h"
14#include "utils.h"
15#include "lib.h"
16
17extern void thirty_two_instruction_loop(u64 loops);
18
19static void setup_event(struct event *e, u64 config, char *name)
20{
21	event_init_opts(e, config, PERF_TYPE_HARDWARE, name);
22
23	e->attr.disabled = 1;
24	e->attr.exclude_kernel = 1;
25	e->attr.exclude_hv = 1;
26	e->attr.exclude_idle = 1;
27}
28
29static int do_count_loop(struct event *events, u64 instructions,
30			 u64 overhead, bool report)
31{
32	s64 difference, expected;
33	double percentage;
34
35	prctl(PR_TASK_PERF_EVENTS_ENABLE);
36
37	/* Run for 1M instructions */
38	thirty_two_instruction_loop(instructions >> 5);
39
40	prctl(PR_TASK_PERF_EVENTS_DISABLE);
41
42	event_read(&events[0]);
43	event_read(&events[1]);
44
45	expected = instructions + overhead;
46	difference = events[0].result.value - expected;
47	percentage = (double)difference / events[0].result.value * 100;
48
49	if (report) {
50		event_report(&events[0]);
51		event_report(&events[1]);
52
53		printf("Looped for %llu instructions, overhead %llu\n", instructions, overhead);
54		printf("Expected %llu\n", expected);
55		printf("Actual   %llu\n", events[0].result.value);
56		printf("Delta    %lld, %f%%\n", difference, percentage);
57	}
58
59	event_reset(&events[0]);
60	event_reset(&events[1]);
61
62	if (difference < 0)
63		difference = -difference;
64
65	/* Tolerate a difference below 0.0001 % */
66	difference *= 10000 * 100;
67	if (difference / events[0].result.value)
68		return -1;
69
70	return 0;
71}
72
73/* Count how many instructions it takes to do a null loop */
74static u64 determine_overhead(struct event *events)
75{
76	u64 current, overhead;
77	int i;
78
79	do_count_loop(events, 0, 0, false);
80	overhead = events[0].result.value;
81
82	for (i = 0; i < 100; i++) {
83		do_count_loop(events, 0, 0, false);
84		current = events[0].result.value;
85		if (current < overhead) {
86			printf("Replacing overhead %llu with %llu\n", overhead, current);
87			overhead = current;
88		}
89	}
90
91	return overhead;
92}
93
94static int test_body(void)
95{
96	struct event events[2];
97	u64 overhead;
98
99	setup_event(&events[0], PERF_COUNT_HW_INSTRUCTIONS, "instructions");
100	setup_event(&events[1], PERF_COUNT_HW_CPU_CYCLES, "cycles");
101
102	if (event_open(&events[0])) {
103		perror("perf_event_open");
104		return -1;
105	}
106
107	if (event_open_with_group(&events[1], events[0].fd)) {
108		perror("perf_event_open");
109		return -1;
110	}
111
112	overhead = determine_overhead(events);
113	printf("Overhead of null loop: %llu instructions\n", overhead);
114
115	/* Run for 1Mi instructions */
116	FAIL_IF(do_count_loop(events, 1000000, overhead, true));
117
118	/* Run for 10Mi instructions */
119	FAIL_IF(do_count_loop(events, 10000000, overhead, true));
120
121	/* Run for 100Mi instructions */
122	FAIL_IF(do_count_loop(events, 100000000, overhead, true));
123
124	/* Run for 1Bi instructions */
125	FAIL_IF(do_count_loop(events, 1000000000, overhead, true));
126
127	/* Run for 16Bi instructions */
128	FAIL_IF(do_count_loop(events, 16000000000, overhead, true));
129
130	/* Run for 64Bi instructions */
131	FAIL_IF(do_count_loop(events, 64000000000, overhead, true));
132
133	event_close(&events[0]);
134	event_close(&events[1]);
135
136	return 0;
137}
138
139static int count_instructions(void)
140{
141	return eat_cpu(test_body);
142}
143
144int main(void)
145{
146	return test_harness(count_instructions, "count_instructions");
147}
148