// `int messages' represents the number of messages to be sent
struct timespec tp[messages];

for (int i = 0; i < messages; i++) {
    /**
     * Prepare WR with an sge that points to tv_nsec of tp[i].
     * By using an array of timespecs, it is guaranteed that
     * the timestamp will not be overwritten.
     */

    clock_gettime(CLOCK_MONOTONIC, &tp[i]);
    ibv_post_send();
}