148 lines · c
1// SPDX-License-Identifier: GPL-2.0-only2/*3 * Copyright 2013, Michael Ellerman, IBM Corp.4 */5 6#define _GNU_SOURCE7 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