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* net/sched/sch_cbq.c Class-Based Queueing discipline.
*
* 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>
*
*/
#include <asm/uaccess.h>
#include <asm/system.h>
#include <asm/bitops.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/socket.h>
#include <linux/sockios.h>
#include <linux/in.h>
#include <linux/errno.h>
#include <linux/interrupt.h>
#include <linux/if_ether.h>
#include <linux/inet.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/notifier.h>
#include <linux/module.h>
#include <net/ip.h>
#include <net/route.h>
#include <linux/skbuff.h>
#include <net/sock.h>
#include <net/pkt_sched.h>
/* Class-Based Queueing (CBQ) algorithm.
=======================================
Sources: [1] Sally Floyd and Van Jacobson, "Link-sharing and Resource
Management Models for Packet Networks",
IEEE/ACM Transactions on Networking, Vol.3, No.4, 1995
[2] Sally Floyd, "Notes on CBQ and Guaranted Service", 1995
[3] Sally Floyd, "Notes on Class-Based Queueing: Setting
Parameters", 1996
Algorithm skeleton is taken from from NS simulator cbq.cc.
-----------------------------------------------------------------------
Differences from NS version.
--- WRR algorith is different. Our version looks more reasonable :-)
and fair when quanta are allowed to be less than MTU.
--- cl->aveidle is REALLY limited from below by cl->minidle.
Seems, it was bug in NS.
--- Purely lexical change: "depth" -> "level", "maxdepth" -> "toplevel".
When depth increases we expect, that the thing becomes lower, does not it? :-)
Besides that, "depth" word is semantically overloaded ---
"token bucket depth", "sfq depth"... Besides that, the algorithm
was called "top-LEVEL sharing".
PROBLEM.
--- Linux has no EOI event at the moment, so that we cannot
estimate true class idle time. Three workarounds are possible,
all of them have drawbacks:
1. (as now) Consider the next dequeue event as sign that
previous packet is finished. It is wrong because of ping-pong
buffers, but on permanently loaded link it is true.
2. (NS approach) Use as link busy time estimate skb->leb/"physical
bandwidth". Even more wrong f.e. on ethernet real busy time much
higher because of collisions.
3. (seems, the most clever) Split net bh to two parts:
NETRX_BH (for received packets) and preserve NET_BH for transmitter.
It will not require driver changes (NETRX_BH flag will be set
in netif_rx), but will allow to trace EOIs more precisely
and will save useless checks in net_bh. Besides that we will
have to eliminate random calling hard_start_xmit with dev->tbusy flag
(done) and to drop failure_q --- i.e. if !dev->tbusy hard_start_xmit
MUST succeed; failed packets will be dropped on the floor.
*/
#define CBQ_TOPLEVEL_SHARING
/* #define CBQ_NO_TRICKERY */
#define CBQ_CLASSIFIER(skb, q) ((q)->fallback_class)
struct cbq_class
{
/* Parameters */
int priority; /* priority */
#ifdef CBQ_TOPLEVEL_SHARING
int level; /* level of the class in hierarchy:
0 for leaf classes, and maximal
level of childrens + 1 for nodes.
*/
#endif
long maxidle; /* Class paramters: see below. */
long minidle;
int filter_log;
#ifndef CBQ_NO_TRICKERY
long extradelay;
#endif
long quantum; /* Allotment per WRR round */
long rquantum; /* Relative allotment: see below */
int cell_log;
unsigned long L_tab[256];
struct Qdisc *qdisc; /* ptr to CBQ discipline */
struct cbq_class *root; /* Ptr to root class;
root can be not unique.
*/
struct cbq_class *parent; /* Ptr to parent in the class tree */
struct cbq_class *borrow; /* NULL if class is bandwidth limited;
parent otherwise */
struct Qdisc *q; /* Elementary queueing discipline */
struct cbq_class *next; /* next class in this priority band */
struct cbq_class *next_alive; /* next class with backlog in this priority band */
/* Variables */
psched_time_t last;
psched_time_t undertime;
long avgidle;
long deficit; /* Saved deficit for WRR */
char awake; /* Class is in alive list */
#if 0
void (*overlimit)(struct cbq_class *cl);
#endif
};
#define L2T(cl,len) ((cl)->L_tab[(len)>>(cl)->cell_log])
struct cbq_sched_data
{
struct cbq_class *classes[CBQ_MAXPRIO]; /* List of all classes */
int nclasses[CBQ_MAXPRIO];
unsigned quanta[CBQ_MAXPRIO];
unsigned mtu;
int cell_log;
unsigned long L_tab[256];
struct cbq_class *fallback_class;
unsigned activemask;
struct cbq_class *active[CBQ_MAXPRIO]; /* List of all classes
with backlog */
struct cbq_class *last_sent;
int last_sent_len;
psched_time_t now; /* Cached timestamp */
struct timer_list wd_timer; /* Wathchdog timer, that
started when CBQ has
backlog, but cannot
transmit just now */
unsigned long wd_expires;
#ifdef CBQ_TOPLEVEL_SHARING
struct cbq_class *borrowed;
int toplevel;
#endif
};
/*
WRR quanta
----------
cl->quantum is number added to class allotment on every round.
cl->rquantum is "relative" quantum.
For real-time classes:
cl->quantum = (cl->rquantum*q->nclasses[prio]*q->mtu)/q->quanta[prio]
where q->quanta[prio] is sum of all rquanta for given priority.
cl->rquantum can be identified with absolute rate of the class
in arbitrary units (f.e. bytes/sec)
In this case, delay introduced by round-robin was estimated by
Sally Floyd [2] as:
D = q->nclasses*q->mtu/(bandwidth/2)
Note, that D does not depend on class rate (it is very bad),
but not much worse than Gallager-Parekh estimate for CSZ
C/R = q->mtu/rate, when real-time classes have close rates.
For not real-time classes this folmula is not necessary,
so that cl->quantum can be set to any reasonable not zero value.
Apparently, it should be proportional to class rate, if the
rate is not zero.
*/
/*
maxidle, minidle, extradelay
----------------------------
CBQ estimator calculates smoothed class idle time cl->aveidle,
considering class as virtual interface with corresponding bandwidth.
When cl->aveidle wants to be less than zero, class is overlimit.
When it is positive, class is underlimit.
* maxidle bounds aveidle from above.
It controls maximal length of burst in this class after
long period of idle time. Burstness of active class
is controlled by filter constant cl->filter_log,
but this number is related to burst length only indirectly.
* minidle is a negative number, normally set to zero.
Setting it to not zero value allows avgidle to drop
below zero, effectively penalizing class, when it is overlimit.
When the class load will decrease, it will take a time to
raise negative avgidle to put the class at limit.
It should be set to zero for leaf classes.
* extradelay is penalty in delay, when a class goes overlimit.
I believe this parameter is useless and confusing.
Setting it to not zero forces class to accumulate
its "idleness" for extradelay and then send BURST of packets
until going to overlimit again. Non-sense.
For details see [1] and [3].
Really, minidle and extradelay are irrelevant to real scheduling
task. As I understand, SF&VJ introduced them to experiment
with CBQ simulator in attempts to fix erratic behaviour
of ancestor-only (and, partially, top-level) algorithm.
WARNING.
User passes them measured in usecs, but cl->minidle,
cl->maxidle and cl->aveidle are scaled with cl->filter_log
in the text of the scheduler.
*/
/*
A packet has just been enqueued on the empty class.
cbq_wakeup_class adds it to the tail of active class list
of its priority band.
*/
static __inline__ void cbq_wakeup_class(struct cbq_class *cl)
{
struct cbq_sched_data *q = (struct cbq_sched_data*)cl->qdisc->data;
int prio = cl->priority;
struct cbq_class *cl_tail;
cl->awake = 1;
cl_tail = q->active[prio];
q->active[prio] = cl;
if (cl_tail != NULL) {
cl->next_alive = cl_tail->next_alive;
cl->deficit = 0;
} else {
cl->next_alive = cl;
q->activemask |= (1<<prio);
cl->deficit = cl->quantum;
}
}
static int
cbq_enqueue(struct sk_buff *skb, struct Qdisc *sch)
{
struct cbq_sched_data *q = (struct cbq_sched_data *)sch->data;
struct cbq_class *cl = CBQ_CLASSIFIER(skb, q);
if (cl->q->enqueue(skb, cl->q) == 1) {
sch->q.qlen++;
#ifdef CBQ_TOPLEVEL_SHARING
if (q->toplevel > 0) {
psched_time_t now;
PSCHED_GET_TIME(now);
if (PSCHED_TLESS(cl->undertime, now))
q->toplevel = 0;
else if (q->toplevel > 1 && cl->borrow &&
PSCHED_TLESS(cl->borrow->undertime, now))
q->toplevel = 1;
}
#endif
if (!cl->awake)
cbq_wakeup_class(cl);
return 1;
}
return 0;
}
static __inline__ void cbq_delay(struct cbq_sched_data *q, struct cbq_class *cl)
{
long delay;
delay = PSCHED_TDIFF(cl->undertime, q->now);
if (q->wd_expires == 0 || q->wd_expires - delay > 0)
q->wd_expires = delay;
}
static void cbq_watchdog(unsigned long arg)
{
struct Qdisc *sch = (struct Qdisc*)arg;
struct cbq_sched_data *q = (struct cbq_sched_data*)sch->data;
q->wd_timer.expires = 0;
q->wd_timer.function = NULL;
qdisc_wakeup(sch->dev);
}
static __inline__ void
cbq_update(struct cbq_sched_data *q)
{
struct cbq_class *cl;
for (cl = q->last_sent; cl; cl = cl->parent) {
long avgidle = cl->avgidle;
long idle;
/*
(now - last) is total time between packet right edges.
(last_pktlen/rate) is "virtual" busy time, so that
idle = (now - last) - last_pktlen/rate
*/
idle = PSCHED_TDIFF(q->now, cl->last)
- L2T(cl, q->last_sent_len);
/* true_avgidle := (1-W)*true_avgidle + W*idle,
where W=2^{-filter_log}. But cl->avgidle is scaled:
cl->avgidle == true_avgidle/W,
hence:
*/
avgidle += idle - (avgidle>>cl->filter_log);
if (avgidle <= 0) {
/* Overlimit or at-limit */
#ifdef CBQ_NO_TRICKERY
avgidle = 0;
#else
if (avgidle < cl->minidle)
avgidle = cl->minidle;
#endif
/* This line was missing in NS. */
cl->avgidle = avgidle;
/* Calculate expected time, when this class
will be allowed to send.
It will occur, when:
(1-W)*true_avgidle + W*delay = 0, i.e.
idle = (1/W - 1)*(-true_avgidle)
or
idle = (1 - W)*(-cl->avgidle);
That is not all.
We want to set undertime to the moment, when
the class is allowed to start next transmission i.e.
(undertime + next_pktlen/phys_bandwidth)
- now - next_pktlen/rate = idle
or
undertime = now + idle + next_pktlen/rate
- next_pktlen/phys_bandwidth
We do not know next packet length, but can
estimate it with average packet length
or current packet_length.
*/
idle = (-avgidle) - ((-avgidle) >> cl->filter_log);
idle += L2T(q, q->last_sent_len);
idle -= L2T(cl, q->last_sent_len);
PSCHED_TADD2(q->now, idle, cl->undertime);
#ifndef CBQ_NO_TRICKERY
/* Do not forget extra delay :-) */
PSCHED_TADD(cl->undertime, cl->extradelay);
#endif
} else {
/* Underlimit */
PSCHED_SET_PASTPERFECT(cl->undertime);
if (avgidle > cl->maxidle)
cl->avgidle = cl->maxidle;
else
cl->avgidle = avgidle;
}
cl->last = q->now;
}
#ifdef CBQ_TOPLEVEL_SHARING
cl = q->last_sent;
if (q->borrowed && q->toplevel >= q->borrowed->level) {
if (cl->q->q.qlen <= 1 || PSCHED_TLESS(q->now, q->borrowed->undertime))
q->toplevel = CBQ_MAXLEVEL;
else if (q->borrowed != cl)
q->toplevel = q->borrowed->level;
}
#endif
q->last_sent = NULL;
}
static __inline__ int
cbq_under_limit(struct cbq_class *cl)
{
struct cbq_sched_data *q = (struct cbq_sched_data*)cl->qdisc->data;
struct cbq_class *this_cl = cl;
if (PSCHED_IS_PASTPERFECT(cl->undertime) || cl->parent == NULL)
return 1;
if (PSCHED_TLESS(cl->undertime, q->now)) {
q->borrowed = cl;
return 1;
}
while (!PSCHED_IS_PASTPERFECT(cl->undertime) &&
PSCHED_TLESS(q->now, cl->undertime)) {
cl = cl->borrow;
if (cl == NULL
#ifdef CBQ_TOPLEVEL_SHARING
|| cl->level > q->toplevel
#endif
) {
#if 0
this_cl->overlimit(this_cl);
#else
cbq_delay(q, this_cl);
#endif
return 0;
}
}
q->borrowed = cl;
return 1;
}
static __inline__ struct sk_buff *
cbq_dequeue_prio(struct Qdisc *sch, int prio, int fallback)
{
struct cbq_sched_data *q = (struct cbq_sched_data *)sch->data;
struct cbq_class *cl_tail, *cl_prev, *cl;
struct sk_buff *skb;
int deficit;
cl_tail = cl_prev = q->active[prio];
cl = cl_prev->next_alive;
do {
deficit = 0;
/* Start round */
do {
/* Class is empty */
if (cl->q->q.qlen == 0)
goto skip_class;
if (fallback) {
/* Fallback pass: all classes are overlimit;
we send from the first class that is allowed
to borrow.
*/
if (cl->borrow == NULL)
goto skip_class;
} else {
/* Normal pass: check that class is under limit */
if (!cbq_under_limit(cl))
goto skip_class;
}
if (cl->deficit <= 0) {
/* Class exhausted its allotment per this
round.
*/
deficit = 1;
goto next_class;
}
skb = cl->q->dequeue(cl->q);
/* Class did not give us any skb :-(
It could occur if cl->q == "tbf"
*/
if (skb == NULL)
goto skip_class;
cl->deficit -= skb->len;
q->last_sent = cl;
q->last_sent_len = skb->len;
if (cl->deficit <= 0) {
q->active[prio] = cl;
cl = cl->next_alive;
cl->deficit += cl->quantum;
}
return skb;
skip_class:
cl->deficit = 0;
if (cl->q->q.qlen == 0) {
/* Class is empty, declare it dead */
cl_prev->next_alive = cl->next_alive;
cl->awake = 0;
/* Did cl_tail point to it? */
if (cl == cl_tail) {
/* Repair it! */
cl_tail = cl_prev;
/* Was it the last class in this band? */
if (cl == cl_tail) {
/* Kill the band! */
q->active[prio] = NULL;
q->activemask &= ~(1<<prio);
return NULL;
}
}
}
next_class:
cl_prev = cl;
cl = cl->next_alive;
cl->deficit += cl->quantum;
} while (cl_prev != cl_tail);
} while (deficit);
q->active[prio] = cl_prev;
return NULL;
}
static __inline__ struct sk_buff *
cbq_dequeue_1(struct Qdisc *sch, int fallback)
{
struct cbq_sched_data *q = (struct cbq_sched_data *)sch->data;
struct sk_buff *skb;
unsigned activemask;
activemask = q->activemask;
while (activemask) {
int prio = ffz(~activemask);
activemask &= ~(1<<prio);
skb = cbq_dequeue_prio(sch, prio, fallback);
if (skb)
return skb;
}
return NULL;
}
static struct sk_buff *
cbq_dequeue(struct Qdisc *sch)
{
struct sk_buff *skb;
struct cbq_sched_data *q = (struct cbq_sched_data *)sch->data;
PSCHED_GET_TIME(q->now);
if (q->last_sent)
cbq_update(q);
q->wd_expires = 0;
skb = cbq_dequeue_1(sch, 0);
if (skb)
return skb;
/* All the classes are overlimit.
Search for overlimit class, which is allowed to borrow
and use it as fallback case.
*/
#ifdef CBQ_TOPLEVEL_SHARING
q->toplevel = CBQ_MAXLEVEL;
#endif
skb = cbq_dequeue_1(sch, 1);
if (skb)
return skb;
/* No packets in scheduler or nobody wants to give them to us :-(
Sigh... start watchdog timer in the last case. */
if (sch->q.qlen && q->wd_expires) {
if (q->wd_timer.function)
del_timer(&q->wd_timer);
q->wd_timer.function = cbq_watchdog;
q->wd_timer.expires = jiffies + PSCHED_US2JIFFIE(q->wd_expires);
add_timer(&q->wd_timer);
}
return NULL;
}
/* CBQ class maintanance routines */
static void cbq_adjust_levels(struct cbq_class *this)
{
struct cbq_class *cl;
for (cl = this->parent; cl; cl = cl->parent) {
if (cl->level > this->level)
return;
cl->level = this->level + 1;
this = cl;
}
}
static void cbq_normalize_quanta(struct cbq_sched_data *q, int prio)
{
struct cbq_class *cl;
if (q->quanta[prio] == 0)
return;
for (cl = q->classes[prio]; cl; cl = cl->next) {
if (cl->rquantum)
cl->quantum = (cl->rquantum*q->mtu*q->nclasses[prio])/
q->quanta[prio];
}
}
static __inline__ int cbq_unlink_class(struct cbq_class *this)
{
struct cbq_class *cl, **clp;
struct cbq_sched_data *q = (struct cbq_sched_data*)this->qdisc->data;
for (clp = &q->classes[this->priority]; (cl = *clp) != NULL;
clp = &cl->next) {
if (cl == this) {
*clp = cl->next;
return 0;
}
}
return -ENOENT;
}
static int cbq_prune(struct cbq_class *this)
{
struct cbq_class *cl;
int prio = this->priority;
struct cbq_sched_data *q = (struct cbq_sched_data*)this->qdisc->data;
qdisc_reset(this->q);
if (cbq_unlink_class(this))
return -ENOENT;
if (this->awake) {
struct cbq_class *cl_prev = q->active[prio];
do {
cl = cl_prev->next_alive;
if (cl == this) {
cl_prev->next_alive = cl->next_alive;
if (cl == q->active[prio]) {
q->active[prio] = cl;
if (cl == q->active[prio]) {
q->active[prio] = NULL;
q->activemask &= ~(1<<prio);
break;
}
}
cl = cl->next_alive;
cl->deficit += cl->quantum;
break;
}
} while ((cl_prev = cl) != q->active[prio]);
}
--q->nclasses[prio];
if (this->rquantum) {
q->quanta[prio] -= this->rquantum;
cbq_normalize_quanta(q, prio);
}
if (q->fallback_class == this)
q->fallback_class = NULL;
this->parent = NULL;
this->borrow = NULL;
this->root = this;
this->qdisc = NULL;
return 0;
}
static int cbq_graft(struct cbq_class *this, struct cbq_class *parent)
{
struct cbq_class *cl, **clp;
int prio = this->priority;
struct cbq_sched_data *q = (struct cbq_sched_data*)this->qdisc->data;
qdisc_reset(this->q);
for (clp = &q->classes[prio]; (cl = *clp) != NULL; clp = &cl->next) {
if (cl == this)
return -EBUSY;
}
cl->next = NULL;
*clp = cl;
cl->parent = parent;
cl->borrow = parent;
cl->root = parent ? parent->root : cl;
++q->nclasses[prio];
if (this->rquantum) {
q->quanta[prio] += this->rquantum;
cbq_normalize_quanta(q, prio);
}
cbq_adjust_levels(this);
return 0;
}
static void
cbq_reset(struct Qdisc* sch)
{
struct cbq_sched_data *q = (struct cbq_sched_data *)sch->data;
struct cbq_class *cl;
int prio;
q->activemask = 0;
q->last_sent = NULL;
if (q->wd_timer.function) {
del_timer(&q->wd_timer);
q->wd_timer.expires = 0;
q->wd_timer.function = NULL;
}
#ifdef CBQ_TOPLEVEL_SHARING
q->toplevel = CBQ_MAXLEVEL;
#endif
for (prio = 0; prio < CBQ_MAXPRIO; prio++) {
q->active[prio] = NULL;
for (cl = q->classes[prio]; cl; cl = cl->next) {
qdisc_reset(cl->q);
cl->next_alive = NULL;
PSCHED_SET_PASTPERFECT(cl->undertime);
cl->avgidle = 0;
cl->deficit = 0;
cl->awake = 0;
}
}
}
static void
cbq_destroy(struct Qdisc* sch)
{
struct cbq_sched_data *q = (struct cbq_sched_data *)sch->data;
struct cbq_class *cl, **clp;
int prio;
for (prio = 0; prio < CBQ_MAXPRIO; prio++) {
struct cbq_class *cl_head = q->classes[prio];
for (clp = &cl_head; (cl=*clp) != NULL; clp = &cl->next) {
qdisc_destroy(cl->q);
kfree(cl);
}
}
}
static int cbq_control(struct Qdisc *sch, void *arg)
{
struct cbq_sched_data *q;
q = (struct cbq_sched_data *)sch->data;
/* Do attachment here. It is the last thing to do. */
return -EINVAL;
}
static int cbq_init(struct Qdisc *sch, void *arg)
{
struct cbq_sched_data *q;
struct cbqctl *ctl = (struct cbqctl*)arg;
q = (struct cbq_sched_data *)sch->data;
init_timer(&q->wd_timer);
q->wd_timer.data = (unsigned long)sch;
#ifdef CBQ_TOPLEVEL_SHARING
q->toplevel = CBQ_MAXLEVEL;
#endif
return 0;
}
struct Qdisc_ops cbq_ops =
{
NULL,
"cbq",
0,
sizeof(struct cbq_sched_data),
cbq_enqueue,
cbq_dequeue,
cbq_reset,
cbq_destroy,
cbq_init,
cbq_control,
};
#ifdef MODULE
int init_module(void)
{
int err;
/* Load once and never free it. */
MOD_INC_USE_COUNT;
err = register_qdisc(&cbq_ops);
if (err)
MOD_DEC_USE_COUNT;
return err;
}
void cleanup_module(void)
{
}
#endif
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