// Global variable
struct timespec tp; 

void * t_function(void * ctx)
{
    while (1) {   
        clock_gettime(CLOCK_MONOTONIC, &tp);
    }   

    return NULL;
}

pthread_t t_thread;
pthread_create(&t_thread, NULL, t_function, NULL);

// `int messages' represents the number of messages to be sent
for (int i = 0; i < messages; i++) {
    /**
     * Prepare WR with sge that points to tp.tv_nsec. It will
     * continue to change since the thread continues to run in the
     * background.
     */

    // No need to invoke clock_gettime() here
    ibv_post_send(); // Post prepared WR
}