def do_part_upload(args):
    """
    Upload a part of a MultiPartUpload

    Open the target file and read in a chunk. Since we can't pickle
    S3Connection or MultiPartUpload objects, we have to reconnect and lookup
    the MPU object with each part upload.

    :type args: tuple of (string, string, string, int, int, int)
    :param args: The actual arguments of this method. Due to lameness of
                 multiprocessing, we have to extract these outside of the
                 function definition.

                 The arguments are: S3 Bucket name, MultiPartUpload id, file
                 name, the part number, part offset, part size
    """
    # Multiprocessing args lameness
    bucket_name, mpu_id, fname, i, start, size, secure, max_tries, current_tries = args
    logger.debug("do_part_upload got args: %s" % (args,))

    # Connect to S3, get the MultiPartUpload
    s3 = boto.connect_s3(calling_format=OrdinaryCallingFormat())
    s3.is_secure = secure
    bucket = s3.lookup(bucket_name)
    mpu = None
    for mp in bucket.list_multipart_uploads():
        if mp.id == mpu_id:
            mpu = mp
            break
    if mpu is None:
        raise Exception("Could not find MultiPartUpload %s" % mpu_id)

    # Read the chunk from the file
    fp = open(fname, 'rb')
    fp.seek(start)
    data = fp.read(size)
    fp.close()
    if not data:
        raise Exception("Unexpectedly tried to read an empty chunk")

    def progress(x,y):
        logger.debug("Part %d: %0.2f%%" % (i+1, 100.*x/y))

    try:
        # Do the upload
        t1 = time.time()
        mpu.upload_part_from_file(StringIO(data), i+1, cb=progress)

        # Print some timings
        t2 = time.time() - t1
        s = len(data)/1024./1024.
        logger.info("Uploaded part %s (%0.2fM) in %0.2fs at %0.2fMBps" % (i+1, s, t2, s/t2))
    except Exception as err:
        logger.debug("Retry request %d of max %d times" % (current_tries, max_tries))
        if (current_tries > max_tries):
            logger.error(err)
        else:
            time.sleep(3)
            current_tries += 1
            do_part_download(bucket_name, mpu_id, fname, i, start, size, secure, max_tries, current_tries)