def append_io_req(req, rd, size, cnt):
    """
    Construct a request for the IO throughput test
    Args:
            req: the basic request
            rd: no. of rounds
            size: the size of data to write each time
            cnt: the times to write in each round
    Example:
            append_io_req(rd=5, size=1kB, cnt=1000)
            write 1kB 1000 times using dd, repeat 5 rounds
    """

    req["cmds"]["io"] = dict(rd=rd, size=size, cnt=cnt)
    return req