test-futex.c

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#define NUM_THREADS 4

static int counter1 = 0;
static int counter2 = 0;
static pthread_mutex_t mutex1;
static pthread_mutex_t mutex2;

__attribute__((noinline)) void baz(int *params) {
    int *counter = params[0] == 1 ? &counter1 : &counter2;
    pthread_mutex_t *mutex = params[0] == 1 ? &mutex1 : &mutex2;
    int increment = params[1];
    int sleep_time = params[0] == 1 ? 1000 : 10; // counter1: 1s, counter2: 10ms

    while (1) {
        pthread_mutex_lock(mutex);
        *counter += increment;
        fprintf(stderr, "counter: %d\n", *counter);
        usleep(sleep_time * 1000); // sleep in milliseconds
        pthread_mutex_unlock(mutex);
    }
}

__attribute__((noinline)) void bar(int *params) {
    baz(params);
}

__attribute__((noinline)) void foo(int *params) {
    bar(params);
}

void *modify_counter(void *arg) {
    foo((int *)arg);
    return NULL;
}

int main() {
    pthread_t threads[NUM_THREADS];
    pthread_mutex_init(&mutex1, NULL);
    pthread_mutex_init(&mutex2, NULL);

    int params1[2] = { 1, 1 }; // {counter1, increment}
    int params2[2] = { 2, 1 }; // {counter2, increment}

    pthread_create(&threads[0], NULL, modify_counter, (void *)params1);
    pthread_create(&threads[1], NULL, modify_counter, (void *)params1);
    pthread_create(&threads[2], NULL, modify_counter, (void *)params2);
    pthread_create(&threads[3], NULL, modify_counter, (void *)params2);

    for (int i = 0; i < NUM_THREADS; i++) {
        pthread_join(threads[i], NULL);
    }

    pthread_mutex_destroy(&mutex1);
    pthread_mutex_destroy(&mutex2);

    printf("Final counter1 value: %d\n", counter1);
    printf("Final counter2 value: %d\n", counter2);

    return 0;
}

⋊> /w/k/b/libbpf-tools on master ◦ sudo ./futexctn -s -m -p $(pidof test-futex) 60 1                                                                                                                      11:03:46
Summarize futex contention latency, hit ctrl-c to exit



test-futex[216569] lock 0x612a05ebf0a0 contended 59 times, 999 avg msecs [max: 1000 msecs, min 999 msecs]
     msecs               : count    distribution
         0 -> 1          : 0        |                                        |
         2 -> 3          : 0        |                                        |
         4 -> 7          : 0        |                                        |
         8 -> 15         : 0        |                                        |
        16 -> 31         : 0        |                                        |
        32 -> 63         : 0        |                                        |
        64 -> 127        : 0        |                                        |
       128 -> 255        : 0        |                                        |
       256 -> 511        : 0        |                                        |
       512 -> 1023       : 59       |****************************************|


test-futex[216569] lock 0x612a05ebf0e0 contended 5930 times, 9 avg msecs [max: 10 msecs, min 9 msecs]
     msecs               : count    distribution
         0 -> 1          : 0        |                                        |
         2 -> 3          : 0        |                                        |
         4 -> 7          : 0        |                                        |
         8 -> 15         : 5930     |****************************************|

⋊> /w/k/b/libbpf-tools on master ◦ sudo ./futexctn -l 0x612a05ebf0e0 -m -p $(pidof test-futex) 60 1                                                                                                       11:05:21
Summarize futex contention latency, hit ctrl-c to exit



test-futex[216572] lock 0x612a05ebf0e0 contended 739 times, 9 avg msecs [max: 10 msecs, min 9 msecs]
    -
    __lll_lock_wait_private
    baz
    bar
    foo
    modify_counter
    pthread_condattr_setpshared
    clone
    -
     msecs               : count    distribution
         0 -> 1          : 0        |                                        |
         2 -> 3          : 0        |                                        |
         4 -> 7          : 0        |                                        |
         8 -> 15         : 739      |****************************************|


test-futex[216573] lock 0x612a05ebf0e0 contended 5183 times, 9 avg msecs [max: 10 msecs, min 9 msecs]
    -
    __lll_lock_wait_private
    baz
    bar
    foo
    modify_counter
    pthread_condattr_setpshared
    clone
    -
     msecs               : count    distribution
         0 -> 1          : 0        |                                        |
         2 -> 3          : 0        |                                        |
         4 -> 7          : 0        |                                        |
         8 -> 15         : 5183     |****************************************|

test-futex[216572] lock 0x612a05ebf0e0 contended 2698 times, 10 avg msecs [max: 13 msecs, min 9 msecs]
    -
    __lll_lock_wait_private
    baz
    bar
    foo
    modify_counter
    pthread_condattr_setpshared
    clone
    -
     msecs               : count    distribution
         0 -> 1          : 0        |                                        |
         2 -> 3          : 0        |                                        |
         4 -> 7          : 0        |                                        |
         8 -> 15         : 2698     |****************************************|


test-futex[216572] lock 0x612a05ebf0e0 contended 3214 times, 10 avg msecs [max: 14 msecs, min 8 msecs]
    -
    __lll_lock_wait_private
    baz
    bar
    foo
    modify_counter
    pthread_condattr_setpshared
    clone
    -
     msecs               : count    distribution
         0 -> 1          : 0        |                                        |
         2 -> 3          : 0        |                                        |
         4 -> 7          : 0        |                                        |
         8 -> 15         : 3214     |****************************************|