enable_all! / disable_all! (PR_TASK_PERF_EVENTS_DISABLE) is per-thread #59

#define _GNU_SOURCE
#include <stdio.h>
#include <string.h>
#include <stdint.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/prctl.h>
#include <sys/syscall.h>
#include <linux/perf_event.h>

static pthread_barrier_t go, done;

static volatile uint64_t sink;
static void burn(void) {
    uint64_t x = 0;
    for (uint64_t i = 0; i < 200000000ULL; i++)
        x += i * 0x9e3779b97f4a7c15ULL;
    sink = x;
}

static uint64_t read_counter(int fd) {
    uint64_t v; read(fd, &v, sizeof(v)); return v;
}

static int open_sw_counter(void) {
    struct perf_event_attr a = { .size = sizeof(a),
        .type = PERF_TYPE_SOFTWARE, .config = PERF_COUNT_SW_CPU_CLOCK };
    return syscall(__NR_perf_event_open, &a, 0, -1, -1, 0);
}

static void *worker(void *arg) {
    int fd = open_sw_counter();
    pthread_barrier_wait(&go);
    uint64_t c0 = read_counter(fd);
    burn();
    printf("  worker: %lu\n", read_counter(fd) - c0);
    pthread_barrier_wait(&done);
    close(fd);
    return NULL;
}

int main(void) {
    pthread_barrier_init(&go, NULL, 2);
    pthread_barrier_init(&done, NULL, 2);
    int fd = open_sw_counter();
    pthread_t tid;
    pthread_create(&tid, NULL, worker, NULL);

    prctl(PR_TASK_PERF_EVENTS_DISABLE);
    sleep(1);

    pthread_barrier_wait(&go);
    uint64_t c0 = read_counter(fd);
    burn();
    printf("  main:   %lu (expected 0, events disabled)\n",
           read_counter(fd) - c0);
    pthread_barrier_wait(&done);

    pthread_join(tid, NULL);
    close(fd);
}