linux-imx

/* SPDX-License-Identifier: GPL-2.0 */

#ifndef __NET_SCHED_RED_H

#define __NET_SCHED_RED_H

​

#include <linux/types.h>

#include <linux/bug.h>

#include <net/pkt_sched.h>

#include <net/inet_ecn.h>

#include <net/dsfield.h>

#include <linux/reciprocal_div.h>

​

/*  Random Early Detection (RED) algorithm.

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

​

    Source: Sally Floyd and Van Jacobson, "Random Early Detection Gateways

    for Congestion Avoidance", 1993, IEEE/ACM Transactions on Networking.

​

    This file codes a "divisionless" version of RED algorithm

    as written down in Fig.17 of the paper.

​

    Short description.

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

​

    When a new packet arrives we calculate the average queue length:

​

    avg = (1-W)*avg + W*current_queue_len,

​

    W is the filter time constant (chosen as 2^(-Wlog)), it controls

    the inertia of the algorithm. To allow larger bursts, W should be

    decreased.

​

    if (avg > th_max) -> packet marked (dropped).

    if (avg < th_min) -> packet passes.

    if (th_min < avg < th_max) we calculate probability:

​

    Pb = max_P * (avg - th_min)/(th_max-th_min)

​

    and mark (drop) packet with this probability.

    Pb changes from 0 (at avg==th_min) to max_P (avg==th_max).

    max_P should be small (not 1), usually 0.01..0.02 is good value.

​

    max_P is chosen as a number, so that max_P/(th_max-th_min)

    is a negative power of two in order arithmetics to contain

    only shifts.

​

​

    Parameters, settable by user:

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

​

    qth_min     - bytes (should be < qth_max/2)

    qth_max     - bytes (should be at least 2*qth_min and less limit)

    Wlog            - bits (<32) log(1/W).

    Plog            - bits (<32)

​

    Plog is related to max_P by formula:

​

    max_P = (qth_max-qth_min)/2^Plog;

​

    F.e. if qth_max=128K and qth_min=32K, then Plog=22

    corresponds to max_P=0.02

​

    Scell_log

    Stab