1 /* 2 * Copyright 2013, Michael Ellerman, IBM Corp. 3 * Licensed under GPLv2. 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
