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
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