timespec_add
vcpu_dirty_total = timespec_add(vcpu_dirty_total, ts_diff);
get_dirty_log_total = timespec_add(get_dirty_log_total,
clear_dirty_log_total = timespec_add(clear_dirty_log_total,
total = timespec_add(total, ts_diff);
struct timespec timespec_add(struct timespec ts1, struct timespec ts2);
target = timespec_add(now, NSEC_PER_SEC/2);
target = timespec_add(now, TARGET_TIMEOUT); /* 100ms */
rel = timespec_add(rel, ns);
target = timespec_add(now, ns);
target = timespec_add(now, ns);
target = timespec_add(start, ns);