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 
17 extern void thirty_two_instruction_loop(u64 loops);
18 
19 static 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 
29 static 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 */
74 static 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 
94 static 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 
139 static int count_instructions(void)
140 {
141 	return eat_cpu(test_body);
142 }
143 
144 int main(void)
145 {
146 	return test_harness(count_instructions, "count_instructions");
147 }
148