// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright 2013, Michael Ellerman, IBM Corp.
 */

#define _GNU_SOURCE

#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include <sys/prctl.h>

#include "event.h"
#include "utils.h"
#include "lib.h"

extern void thirty_two_instruction_loop(u64 loops);

static void setup_event(struct event *e, u64 config, char *name)
{
        event_init_opts(e, config, PERF_TYPE_HARDWARE, name);

        e->attr.disabled = 1;
        e->attr.exclude_kernel = 1;
        e->attr.exclude_hv = 1;
        e->attr.exclude_idle = 1;
}

static int do_count_loop(struct event *events, u64 instructions,
                         u64 overhead, bool report)
{
        s64 difference, expected;
        double percentage;

        prctl(PR_TASK_PERF_EVENTS_ENABLE);

        /* Run for 1M instructions */
        thirty_two_instruction_loop(instructions >> 5);

        prctl(PR_TASK_PERF_EVENTS_DISABLE);

        event_read(&events[0]);
        event_read(&events[1]);

        expected = instructions + overhead;
        difference = events[0].result.value - expected;
        percentage = (double)difference / events[0].result.value * 100;

        if (report) {
                event_report(&events[0]);
                event_report(&events[1]);

                printf("Looped for %llu instructions, overhead %llu\n", instructions, overhead);
                printf("Expected %llu\n", expected);
                printf("Actual   %llu\n", events[0].result.value);
                printf("Delta    %lld, %f%%\n", difference, percentage);
        }

        event_reset(&events[0]);
        event_reset(&events[1]);

        if (difference < 0)
                difference = -difference;

        /* Tolerate a difference below 0.0001 % */
        difference *= 10000 * 100;
        if (difference / events[0].result.value)
                return -1;

        return 0;
}

/* Count how many instructions it takes to do a null loop */
static u64 determine_overhead(struct event *events)
{
        u64 current, overhead;
        int i;

        do_count_loop(events, 0, 0, false);
        overhead = events[0].result.value;

        for (i = 0; i < 100; i++) {
                do_count_loop(events, 0, 0, false);
                current = events[0].result.value;
                if (current < overhead) {
                        printf("Replacing overhead %llu with %llu\n", overhead, current);
                        overhead = current;
                }
        }

        return overhead;
}

static int test_body(void)
{
        struct event events[2];
        u64 overhead;

        setup_event(&events[0], PERF_COUNT_HW_INSTRUCTIONS, "instructions");
        setup_event(&events[1], PERF_COUNT_HW_CPU_CYCLES, "cycles");

        if (event_open(&events[0])) {
                perror("perf_event_open");
                return -1;
        }

        if (event_open_with_group(&events[1], events[0].fd)) {
                perror("perf_event_open");
                return -1;
        }

        overhead = determine_overhead(events);
        printf("Overhead of null loop: %llu instructions\n", overhead);

        /* Run for 1Mi instructions */
        FAIL_IF(do_count_loop(events, 1000000, overhead, true));

        /* Run for 10Mi instructions */
        FAIL_IF(do_count_loop(events, 10000000, overhead, true));

        /* Run for 100Mi instructions */
        FAIL_IF(do_count_loop(events, 100000000, overhead, true));

        /* Run for 1Bi instructions */
        FAIL_IF(do_count_loop(events, 1000000000, overhead, true));

        /* Run for 16Bi instructions */
        FAIL_IF(do_count_loop(events, 16000000000, overhead, true));

        /* Run for 64Bi instructions */
        FAIL_IF(do_count_loop(events, 64000000000, overhead, true));

        event_close(&events[0]);
        event_close(&events[1]);

        return 0;
}

static int count_instructions(void)
{
        return eat_cpu(test_body);
}

int main(void)
{
        return test_harness(count_instructions, "count_instructions");
}