linux-imx

/*

 * net/sched/sch_tbf.c  Token Bucket Filter queue.

 *

 *      This program is free software; you can redistribute it and/or

 *      modify it under the terms of the GNU General Public License

 *      as published by the Free Software Foundation; either version

 *      2 of the License, or (at your option) any later version.

 *

 * Authors: Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>

 *      Dmitry Torokhov <dtor@mail.ru> - allow attaching inner qdiscs -

 *                       original idea by Martin Devera

 *

 */

​

#include <linux/module.h>

#include <linux/types.h>

#include <linux/kernel.h>

#include <linux/string.h>

#include <linux/errno.h>

#include <linux/skbuff.h>

#include <net/netlink.h>

#include <net/sch_generic.h>

#include <net/pkt_sched.h>

​

​

/*  Simple Token Bucket Filter.

    =======================================

​

    SOURCE.

    -------

​

    None.

​

    Description.

    ------------

​

    A data flow obeys TBF with rate R and depth B, if for any

    time interval t_i...t_f the number of transmitted bits

    does not exceed B + R*(t_f-t_i).

​

    Packetized version of this definition:

    The sequence of packets of sizes s_i served at moments t_i

    obeys TBF, if for any i<=k:

​

    s_i+....+s_k <= B + R*(t_k - t_i)

​

    Algorithm.

    ----------

​

    Let N(t_i) be B/R initially and N(t) grow continuously with time as:

​

    N(t+delta) = min{B/R, N(t) + delta}

​

    If the first packet in queue has length S, it may be

    transmitted only at the time t_* when S/R <= N(t_*),

    and in this case N(t) jumps:

​

    N(t_* + 0) = N(t_* - 0) - S/R.

​

​

​

    Actually, QoS requires two TBF to be applied to a data stream.

    One of them controls steady state burst size, another