[PKT_SCHED]: Generic RED layer
Extracts the RED algorithm from sch_red.c and puts it into include/net/red.h for use by other RED based modules. The statistics are extended to be more fine grained in order to differ between probability/forced marks/drops. We now reset the average queue length when setting new parameters, leaving it might result in an unreasonable qavg for a while depending on the value of W. Signed-off-by: Thomas Graf <tgraf@suug.ch> Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
This commit is contained in:
Thomas Graf
Thomas Graf
Родитель
1758ee0ea2
Коммит
a783474591
|
|
@ -0,0 +1,325 @@
|
|||
#ifndef __NET_SCHED_RED_H
|
||||
#define __NET_SCHED_RED_H
|
||||
|
||||
#include <linux/config.h>
|
||||
#include <linux/types.h>
|
||||
#include <net/pkt_sched.h>
|
||||
#include <net/inet_ecn.h>
|
||||
#include <net/dsfield.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
|
||||
|
||||
Lookup table for log((1-W)^(t/t_ave).
|
||||
|
||||
|
||||
NOTES:
|
||||
|
||||
Upper bound on W.
|
||||
-----------------
|
||||
|
||||
If you want to allow bursts of L packets of size S,
|
||||
you should choose W:
|
||||
|
||||
L + 1 - th_min/S < (1-(1-W)^L)/W
|
||||
|
||||
th_min/S = 32 th_min/S = 4
|
||||
|
||||
log(W) L
|
||||
-1 33
|
||||
-2 35
|
||||
-3 39
|
||||
-4 46
|
||||
-5 57
|
||||
-6 75
|
||||
-7 101
|
||||
-8 135
|
||||
-9 190
|
||||
etc.
|
||||
*/
|
||||
|
||||
#define RED_STAB_SIZE 256
|
||||
#define RED_STAB_MASK (RED_STAB_SIZE - 1)
|
||||
|
||||
struct red_stats
|
||||
{
|
||||
u32 prob_drop; /* Early probability drops */
|
||||
u32 prob_mark; /* Early probability marks */
|
||||
u32 forced_drop; /* Forced drops, qavg > max_thresh */
|
||||
u32 forced_mark; /* Forced marks, qavg > max_thresh */
|
||||
u32 pdrop; /* Drops due to queue limits */
|
||||
u32 other; /* Drops due to drop() calls */
|
||||
u32 backlog;
|
||||
};
|
||||
|
||||
struct red_parms
|
||||
{
|
||||
/* Parameters */
|
||||
u32 qth_min; /* Min avg length threshold: A scaled */
|
||||
u32 qth_max; /* Max avg length threshold: A scaled */
|
||||
u32 Scell_max;
|
||||
u32 Rmask; /* Cached random mask, see red_rmask */
|
||||
u8 Scell_log;
|
||||
u8 Wlog; /* log(W) */
|
||||
u8 Plog; /* random number bits */
|
||||
u8 Stab[RED_STAB_SIZE];
|
||||
|
||||
/* Variables */
|
||||
int qcount; /* Number of packets since last random
|
||||
number generation */
|
||||
u32 qR; /* Cached random number */
|
||||
|
||||
unsigned long qavg; /* Average queue length: A scaled */
|
||||
psched_time_t qidlestart; /* Start of current idle period */
|
||||
};
|
||||
|
||||
static inline u32 red_rmask(u8 Plog)
|
||||
{
|
||||
return Plog < 32 ? ((1 << Plog) - 1) : ~0UL;
|
||||
}
|
||||
|
||||
static inline void red_set_parms(struct red_parms *p,
|
||||
u32 qth_min, u32 qth_max, u8 Wlog, u8 Plog,
|
||||
u8 Scell_log, u8 *stab)
|
||||
{
|
||||
/* Reset average queue length, the value is strictly bound
|
||||
* to the parameters below, reseting hurts a bit but leaving
|
||||
* it might result in an unreasonable qavg for a while. --TGR
|
||||
*/
|
||||
p->qavg = 0;
|
||||
|
||||
p->qcount = -1;
|
||||
p->qth_min = qth_min << Wlog;
|
||||
p->qth_max = qth_max << Wlog;
|
||||
p->Wlog = Wlog;
|
||||
p->Plog = Plog;
|
||||
p->Rmask = red_rmask(Plog);
|
||||
p->Scell_log = Scell_log;
|
||||
p->Scell_max = (255 << Scell_log);
|
||||
|
||||
memcpy(p->Stab, stab, sizeof(p->Stab));
|
||||
}
|
||||
|
||||
static inline int red_is_idling(struct red_parms *p)
|
||||
{
|
||||
return !PSCHED_IS_PASTPERFECT(p->qidlestart);
|
||||
}
|
||||
|
||||
static inline void red_start_of_idle_period(struct red_parms *p)
|
||||
{
|
||||
PSCHED_GET_TIME(p->qidlestart);
|
||||
}
|
||||
|
||||
static inline void red_end_of_idle_period(struct red_parms *p)
|
||||
{
|
||||
PSCHED_SET_PASTPERFECT(p->qidlestart);
|
||||
}
|
||||
|
||||
static inline void red_restart(struct red_parms *p)
|
||||
{
|
||||
red_end_of_idle_period(p);
|
||||
p->qavg = 0;
|
||||
p->qcount = -1;
|
||||
}
|
||||
|
||||
static inline unsigned long red_calc_qavg_from_idle_time(struct red_parms *p)
|
||||
{
|
||||
psched_time_t now;
|
||||
long us_idle;
|
||||
int shift;
|
||||
|
||||
PSCHED_GET_TIME(now);
|
||||
us_idle = PSCHED_TDIFF_SAFE(now, p->qidlestart, p->Scell_max);
|
||||
|
||||
/*
|
||||
* The problem: ideally, average length queue recalcultion should
|
||||
* be done over constant clock intervals. This is too expensive, so
|
||||
* that the calculation is driven by outgoing packets.
|
||||
* When the queue is idle we have to model this clock by hand.
|
||||
*
|
||||
* SF+VJ proposed to "generate":
|
||||
*
|
||||
* m = idletime / (average_pkt_size / bandwidth)
|
||||
*
|
||||
* dummy packets as a burst after idle time, i.e.
|
||||
*
|
||||
* p->qavg *= (1-W)^m
|
||||
*
|
||||
* This is an apparently overcomplicated solution (f.e. we have to
|
||||
* precompute a table to make this calculation in reasonable time)
|
||||
* I believe that a simpler model may be used here,
|
||||
* but it is field for experiments.
|
||||
*/
|
||||
|
||||
shift = p->Stab[(us_idle >> p->Scell_log) & RED_STAB_MASK];
|
||||
|
||||
if (shift)
|
||||
return p->qavg >> shift;
|
||||
else {
|
||||
/* Approximate initial part of exponent with linear function:
|
||||
*
|
||||
* (1-W)^m ~= 1-mW + ...
|
||||
*
|
||||
* Seems, it is the best solution to
|
||||
* problem of too coarse exponent tabulation.
|
||||
*/
|
||||
us_idle = (p->qavg * us_idle) >> p->Scell_log;
|
||||
|
||||
if (us_idle < (p->qavg >> 1))
|
||||
return p->qavg - us_idle;
|
||||
else
|
||||
return p->qavg >> 1;
|
||||
}
|
||||
}
|
||||
|
||||
static inline unsigned long red_calc_qavg_no_idle_time(struct red_parms *p,
|
||||
unsigned int backlog)
|
||||
{
|
||||
/*
|
||||
* NOTE: p->qavg is fixed point number with point at Wlog.
|
||||
* The formula below is equvalent to floating point
|
||||
* version:
|
||||
*
|
||||
* qavg = qavg*(1-W) + backlog*W;
|
||||
*
|
||||
* --ANK (980924)
|
||||
*/
|
||||
return p->qavg + (backlog - (p->qavg >> p->Wlog));
|
||||
}
|
||||
|
||||
static inline unsigned long red_calc_qavg(struct red_parms *p,
|
||||
unsigned int backlog)
|
||||
{
|
||||
if (!red_is_idling(p))
|
||||
return red_calc_qavg_no_idle_time(p, backlog);
|
||||
else
|
||||
return red_calc_qavg_from_idle_time(p);
|
||||
}
|
||||
|
||||
static inline u32 red_random(struct red_parms *p)
|
||||
{
|
||||
return net_random() & p->Rmask;
|
||||
}
|
||||
|
||||
static inline int red_mark_probability(struct red_parms *p, unsigned long qavg)
|
||||
{
|
||||
/* The formula used below causes questions.
|
||||
|
||||
OK. qR is random number in the interval 0..Rmask
|
||||
i.e. 0..(2^Plog). If we used floating point
|
||||
arithmetics, it would be: (2^Plog)*rnd_num,
|
||||
where rnd_num is less 1.
|
||||
|
||||
Taking into account, that qavg have fixed
|
||||
point at Wlog, and Plog is related to max_P by
|
||||
max_P = (qth_max-qth_min)/2^Plog; two lines
|
||||
below have the following floating point equivalent:
|
||||
|
||||
max_P*(qavg - qth_min)/(qth_max-qth_min) < rnd/qcount
|
||||
|
||||
Any questions? --ANK (980924)
|
||||
*/
|
||||
return !(((qavg - p->qth_min) >> p->Wlog) * p->qcount < p->qR);
|
||||
}
|
||||
|
||||
enum {
|
||||
RED_BELOW_MIN_THRESH,
|
||||
RED_BETWEEN_TRESH,
|
||||
RED_ABOVE_MAX_TRESH,
|
||||
};
|
||||
|
||||
static inline int red_cmp_thresh(struct red_parms *p, unsigned long qavg)
|
||||
{
|
||||
if (qavg < p->qth_min)
|
||||
return RED_BELOW_MIN_THRESH;
|
||||
else if (qavg >= p->qth_max)
|
||||
return RED_ABOVE_MAX_TRESH;
|
||||
else
|
||||
return RED_BETWEEN_TRESH;
|
||||
}
|
||||
|
||||
enum {
|
||||
RED_DONT_MARK,
|
||||
RED_PROB_MARK,
|
||||
RED_HARD_MARK,
|
||||
};
|
||||
|
||||
static inline int red_action(struct red_parms *p, unsigned long qavg)
|
||||
{
|
||||
switch (red_cmp_thresh(p, qavg)) {
|
||||
case RED_BELOW_MIN_THRESH:
|
||||
p->qcount = -1;
|
||||
return RED_DONT_MARK;
|
||||
|
||||
case RED_BETWEEN_TRESH:
|
||||
if (++p->qcount) {
|
||||
if (red_mark_probability(p, qavg)) {
|
||||
p->qcount = 0;
|
||||
p->qR = red_random(p);
|
||||
return RED_PROB_MARK;
|
||||
}
|
||||
} else
|
||||
p->qR = red_random(p);
|
||||
|
||||
return RED_DONT_MARK;
|
||||
|
||||
case RED_ABOVE_MAX_TRESH:
|
||||
p->qcount = -1;
|
||||
return RED_HARD_MARK;
|
||||
}
|
||||
|
||||
BUG();
|
||||
return RED_DONT_MARK;
|
||||
}
|
||||
|
||||
#endif
|
||||
Загрузка…
Ссылка в новой задаче