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sch_cbq.c
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sch_cbq.c
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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, <[email protected]>
*
*/
#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/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 Guaranteed Service", 1995
[3] Sally Floyd, "Notes on Class-Based Queueing: Setting
Parameters", 1996
[4] Sally Floyd and Michael Speer, "Experimental Results
for Class-Based Queueing", 1998, not published.
-----------------------------------------------------------------------
Algorithm skeleton was taken from NS simulator cbq.cc.
If someone wants to check this code against the LBL version,
he should take into account that ONLY the skeleton was borrowed,
the implementation is different. Particularly:
--- The WRR algorithm is different. Our version looks more
reasonable (I hope) and works when quanta are allowed to be
less than MTU, which is always the case when real time classes
have small rates. Note, that the statement of [3] is
incomplete, delay may actually be estimated even if class
per-round allotment is less than MTU. Namely, if per-round
allotment is W*r_i, and r_1+...+r_k = r < 1
delay_i <= ([MTU/(W*r_i)]*W*r + W*r + k*MTU)/B
In the worst case we have IntServ estimate with D = W*r+k*MTU
and C = MTU*r. The proof (if correct at all) is trivial.
--- It seems that cbq-2.0 is not very accurate. At least, I cannot
interpret some places, which look like wrong translations
from NS. Anyone is advised to find these differences
and explain to me, why I am wrong 8).
--- Linux has no EOI event, so that we cannot estimate true class
idle time. Workaround is to consider the next dequeue event
as sign that previous packet is finished. This is wrong because of
internal device queueing, but on a permanently loaded link it is true.
Moreover, combined with clock integrator, this scheme looks
very close to an ideal solution. */
struct cbq_sched_data;
struct cbq_class
{
struct Qdisc_class_common common;
struct cbq_class *next_alive; /* next class with backlog in this priority band */
/* Parameters */
unsigned char priority; /* class priority */
unsigned char priority2; /* priority to be used after overlimit */
unsigned char ewma_log; /* time constant for idle time calculation */
unsigned char ovl_strategy;
#ifdef CONFIG_NET_CLS_ACT
unsigned char police;
#endif
u32 defmap;
/* Link-sharing scheduler parameters */
long maxidle; /* Class parameters: see below. */
long offtime;
long minidle;
u32 avpkt;
struct qdisc_rate_table *R_tab;
/* Overlimit strategy parameters */
void (*overlimit)(struct cbq_class *cl);
psched_tdiff_t penalty;
/* General scheduler (WRR) parameters */
long allot;
long quantum; /* Allotment per WRR round */
long weight; /* Relative allotment: see below */
struct Qdisc *qdisc; /* Ptr to CBQ discipline */
struct cbq_class *split; /* Ptr to split node */
struct cbq_class *share; /* Ptr to LS parent in the class tree */
struct cbq_class *tparent; /* Ptr to tree parent in the class tree */
struct cbq_class *borrow; /* NULL if class is bandwidth limited;
parent otherwise */
struct cbq_class *sibling; /* Sibling chain */
struct cbq_class *children; /* Pointer to children chain */
struct Qdisc *q; /* Elementary queueing discipline */
/* Variables */
unsigned char cpriority; /* Effective priority */
unsigned char delayed;
unsigned char level; /* level of the class in hierarchy:
0 for leaf classes, and maximal
level of children + 1 for nodes.
*/
psched_time_t last; /* Last end of service */
psched_time_t undertime;
long avgidle;
long deficit; /* Saved deficit for WRR */
psched_time_t penalized;
struct gnet_stats_basic_packed bstats;
struct gnet_stats_queue qstats;
struct gnet_stats_rate_est rate_est;
struct tc_cbq_xstats xstats;
struct tcf_proto *filter_list;
int refcnt;
int filters;
struct cbq_class *defaults[TC_PRIO_MAX+1];
};
struct cbq_sched_data
{
struct Qdisc_class_hash clhash; /* Hash table of all classes */
int nclasses[TC_CBQ_MAXPRIO+1];
unsigned quanta[TC_CBQ_MAXPRIO+1];
struct cbq_class link;
unsigned activemask;
struct cbq_class *active[TC_CBQ_MAXPRIO+1]; /* List of all classes
with backlog */
#ifdef CONFIG_NET_CLS_ACT
struct cbq_class *rx_class;
#endif
struct cbq_class *tx_class;
struct cbq_class *tx_borrowed;
int tx_len;
psched_time_t now; /* Cached timestamp */
psched_time_t now_rt; /* Cached real time */
unsigned pmask;
struct hrtimer delay_timer;
struct qdisc_watchdog watchdog; /* Watchdog timer,
started when CBQ has
backlog, but cannot
transmit just now */
psched_tdiff_t wd_expires;
int toplevel;
u32 hgenerator;
};
#define L2T(cl,len) qdisc_l2t((cl)->R_tab,len)
static __inline__ struct cbq_class *
cbq_class_lookup(struct cbq_sched_data *q, u32 classid)
{
struct Qdisc_class_common *clc;
clc = qdisc_class_find(&q->clhash, classid);
if (clc == NULL)
return NULL;
return container_of(clc, struct cbq_class, common);
}
#ifdef CONFIG_NET_CLS_ACT
static struct cbq_class *
cbq_reclassify(struct sk_buff *skb, struct cbq_class *this)
{
struct cbq_class *cl, *new;
for (cl = this->tparent; cl; cl = cl->tparent)
if ((new = cl->defaults[TC_PRIO_BESTEFFORT]) != NULL && new != this)
return new;
return NULL;
}
#endif
/* Classify packet. The procedure is pretty complicated, but
it allows us to combine link sharing and priority scheduling
transparently.
Namely, you can put link sharing rules (f.e. route based) at root of CBQ,
so that it resolves to split nodes. Then packets are classified
by logical priority, or a more specific classifier may be attached
to the split node.
*/
static struct cbq_class *
cbq_classify(struct sk_buff *skb, struct Qdisc *sch, int *qerr)
{
struct cbq_sched_data *q = qdisc_priv(sch);
struct cbq_class *head = &q->link;
struct cbq_class **defmap;
struct cbq_class *cl = NULL;
u32 prio = skb->priority;
struct tcf_result res;
/*
* Step 1. If skb->priority points to one of our classes, use it.
*/
if (TC_H_MAJ(prio^sch->handle) == 0 &&
(cl = cbq_class_lookup(q, prio)) != NULL)
return cl;
*qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
for (;;) {
int result = 0;
defmap = head->defaults;
/*
* Step 2+n. Apply classifier.
*/
if (!head->filter_list ||
(result = tc_classify_compat(skb, head->filter_list, &res)) < 0)
goto fallback;
if ((cl = (void*)res.class) == NULL) {
if (TC_H_MAJ(res.classid))
cl = cbq_class_lookup(q, res.classid);
else if ((cl = defmap[res.classid&TC_PRIO_MAX]) == NULL)
cl = defmap[TC_PRIO_BESTEFFORT];
if (cl == NULL || cl->level >= head->level)
goto fallback;
}
#ifdef CONFIG_NET_CLS_ACT
switch (result) {
case TC_ACT_QUEUED:
case TC_ACT_STOLEN:
*qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
case TC_ACT_SHOT:
return NULL;
case TC_ACT_RECLASSIFY:
return cbq_reclassify(skb, cl);
}
#endif
if (cl->level == 0)
return cl;
/*
* Step 3+n. If classifier selected a link sharing class,
* apply agency specific classifier.
* Repeat this procdure until we hit a leaf node.
*/
head = cl;
}
fallback:
cl = head;
/*
* Step 4. No success...
*/
if (TC_H_MAJ(prio) == 0 &&
!(cl = head->defaults[prio&TC_PRIO_MAX]) &&
!(cl = head->defaults[TC_PRIO_BESTEFFORT]))
return head;
return cl;
}
/*
A packet has just been enqueued on the empty class.
cbq_activate_class adds it to the tail of active class list
of its priority band.
*/
static __inline__ void cbq_activate_class(struct cbq_class *cl)
{
struct cbq_sched_data *q = qdisc_priv(cl->qdisc);
int prio = cl->cpriority;
struct cbq_class *cl_tail;
cl_tail = q->active[prio];
q->active[prio] = cl;
if (cl_tail != NULL) {
cl->next_alive = cl_tail->next_alive;
cl_tail->next_alive = cl;
} else {
cl->next_alive = cl;
q->activemask |= (1<<prio);
}
}
/*
Unlink class from active chain.
Note that this same procedure is done directly in cbq_dequeue*
during round-robin procedure.
*/
static void cbq_deactivate_class(struct cbq_class *this)
{
struct cbq_sched_data *q = qdisc_priv(this->qdisc);
int prio = this->cpriority;
struct cbq_class *cl;
struct cbq_class *cl_prev = q->active[prio];
do {
cl = cl_prev->next_alive;
if (cl == this) {
cl_prev->next_alive = cl->next_alive;
cl->next_alive = NULL;
if (cl == q->active[prio]) {
q->active[prio] = cl_prev;
if (cl == q->active[prio]) {
q->active[prio] = NULL;
q->activemask &= ~(1<<prio);
return;
}
}
return;
}
} while ((cl_prev = cl) != q->active[prio]);
}
static void
cbq_mark_toplevel(struct cbq_sched_data *q, struct cbq_class *cl)
{
int toplevel = q->toplevel;
if (toplevel > cl->level && !(cl->q->flags&TCQ_F_THROTTLED)) {
psched_time_t now;
psched_tdiff_t incr;
now = psched_get_time();
incr = now - q->now_rt;
now = q->now + incr;
do {
if (cl->undertime < now) {
q->toplevel = cl->level;
return;
}
} while ((cl=cl->borrow) != NULL && toplevel > cl->level);
}
}
static int
cbq_enqueue(struct sk_buff *skb, struct Qdisc *sch)
{
struct cbq_sched_data *q = qdisc_priv(sch);
int uninitialized_var(ret);
struct cbq_class *cl = cbq_classify(skb, sch, &ret);
#ifdef CONFIG_NET_CLS_ACT
q->rx_class = cl;
#endif
if (cl == NULL) {
if (ret & __NET_XMIT_BYPASS)
sch->qstats.drops++;
kfree_skb(skb);
return ret;
}
#ifdef CONFIG_NET_CLS_ACT
cl->q->__parent = sch;
#endif
ret = qdisc_enqueue(skb, cl->q);
if (ret == NET_XMIT_SUCCESS) {
sch->q.qlen++;
sch->bstats.packets++;
sch->bstats.bytes += qdisc_pkt_len(skb);
cbq_mark_toplevel(q, cl);
if (!cl->next_alive)
cbq_activate_class(cl);
return ret;
}
if (net_xmit_drop_count(ret)) {
sch->qstats.drops++;
cbq_mark_toplevel(q, cl);
cl->qstats.drops++;
}
return ret;
}
/* Overlimit actions */
/* TC_CBQ_OVL_CLASSIC: (default) penalize leaf class by adding offtime */
static void cbq_ovl_classic(struct cbq_class *cl)
{
struct cbq_sched_data *q = qdisc_priv(cl->qdisc);
psched_tdiff_t delay = cl->undertime - q->now;
if (!cl->delayed) {
delay += cl->offtime;
/*
Class goes to sleep, so that it will have no
chance to work avgidle. Let's forgive it 8)
BTW cbq-2.0 has a crap in this
place, apparently they forgot to shift it by cl->ewma_log.
*/
if (cl->avgidle < 0)
delay -= (-cl->avgidle) - ((-cl->avgidle) >> cl->ewma_log);
if (cl->avgidle < cl->minidle)
cl->avgidle = cl->minidle;
if (delay <= 0)
delay = 1;
cl->undertime = q->now + delay;
cl->xstats.overactions++;
cl->delayed = 1;
}
if (q->wd_expires == 0 || q->wd_expires > delay)
q->wd_expires = delay;
/* Dirty work! We must schedule wakeups based on
real available rate, rather than leaf rate,
which may be tiny (even zero).
*/
if (q->toplevel == TC_CBQ_MAXLEVEL) {
struct cbq_class *b;
psched_tdiff_t base_delay = q->wd_expires;
for (b = cl->borrow; b; b = b->borrow) {
delay = b->undertime - q->now;
if (delay < base_delay) {
if (delay <= 0)
delay = 1;
base_delay = delay;
}
}
q->wd_expires = base_delay;
}
}
/* TC_CBQ_OVL_RCLASSIC: penalize by offtime classes in hierarchy, when
they go overlimit
*/
static void cbq_ovl_rclassic(struct cbq_class *cl)
{
struct cbq_sched_data *q = qdisc_priv(cl->qdisc);
struct cbq_class *this = cl;
do {
if (cl->level > q->toplevel) {
cl = NULL;
break;
}
} while ((cl = cl->borrow) != NULL);
if (cl == NULL)
cl = this;
cbq_ovl_classic(cl);
}
/* TC_CBQ_OVL_DELAY: delay until it will go to underlimit */
static void cbq_ovl_delay(struct cbq_class *cl)
{
struct cbq_sched_data *q = qdisc_priv(cl->qdisc);
psched_tdiff_t delay = cl->undertime - q->now;
if (test_bit(__QDISC_STATE_DEACTIVATED,
&qdisc_root_sleeping(cl->qdisc)->state))
return;
if (!cl->delayed) {
psched_time_t sched = q->now;
ktime_t expires;
delay += cl->offtime;
if (cl->avgidle < 0)
delay -= (-cl->avgidle) - ((-cl->avgidle) >> cl->ewma_log);
if (cl->avgidle < cl->minidle)
cl->avgidle = cl->minidle;
cl->undertime = q->now + delay;
if (delay > 0) {
sched += delay + cl->penalty;
cl->penalized = sched;
cl->cpriority = TC_CBQ_MAXPRIO;
q->pmask |= (1<<TC_CBQ_MAXPRIO);
expires = ktime_set(0, 0);
expires = ktime_add_ns(expires, PSCHED_TICKS2NS(sched));
if (hrtimer_try_to_cancel(&q->delay_timer) &&
ktime_to_ns(ktime_sub(
hrtimer_get_expires(&q->delay_timer),
expires)) > 0)
hrtimer_set_expires(&q->delay_timer, expires);
hrtimer_restart(&q->delay_timer);
cl->delayed = 1;
cl->xstats.overactions++;
return;
}
delay = 1;
}
if (q->wd_expires == 0 || q->wd_expires > delay)
q->wd_expires = delay;
}
/* TC_CBQ_OVL_LOWPRIO: penalize class by lowering its priority band */
static void cbq_ovl_lowprio(struct cbq_class *cl)
{
struct cbq_sched_data *q = qdisc_priv(cl->qdisc);
cl->penalized = q->now + cl->penalty;
if (cl->cpriority != cl->priority2) {
cl->cpriority = cl->priority2;
q->pmask |= (1<<cl->cpriority);
cl->xstats.overactions++;
}
cbq_ovl_classic(cl);
}
/* TC_CBQ_OVL_DROP: penalize class by dropping */
static void cbq_ovl_drop(struct cbq_class *cl)
{
if (cl->q->ops->drop)
if (cl->q->ops->drop(cl->q))
cl->qdisc->q.qlen--;
cl->xstats.overactions++;
cbq_ovl_classic(cl);
}
static psched_tdiff_t cbq_undelay_prio(struct cbq_sched_data *q, int prio,
psched_time_t now)
{
struct cbq_class *cl;
struct cbq_class *cl_prev = q->active[prio];
psched_time_t sched = now;
if (cl_prev == NULL)
return 0;
do {
cl = cl_prev->next_alive;
if (now - cl->penalized > 0) {
cl_prev->next_alive = cl->next_alive;
cl->next_alive = NULL;
cl->cpriority = cl->priority;
cl->delayed = 0;
cbq_activate_class(cl);
if (cl == q->active[prio]) {
q->active[prio] = cl_prev;
if (cl == q->active[prio]) {
q->active[prio] = NULL;
return 0;
}
}
cl = cl_prev->next_alive;
} else if (sched - cl->penalized > 0)
sched = cl->penalized;
} while ((cl_prev = cl) != q->active[prio]);
return sched - now;
}
static enum hrtimer_restart cbq_undelay(struct hrtimer *timer)
{
struct cbq_sched_data *q = container_of(timer, struct cbq_sched_data,
delay_timer);
struct Qdisc *sch = q->watchdog.qdisc;
psched_time_t now;
psched_tdiff_t delay = 0;
unsigned pmask;
now = psched_get_time();
pmask = q->pmask;
q->pmask = 0;
while (pmask) {
int prio = ffz(~pmask);
psched_tdiff_t tmp;
pmask &= ~(1<<prio);
tmp = cbq_undelay_prio(q, prio, now);
if (tmp > 0) {
q->pmask |= 1<<prio;
if (tmp < delay || delay == 0)
delay = tmp;
}
}
if (delay) {
ktime_t time;
time = ktime_set(0, 0);
time = ktime_add_ns(time, PSCHED_TICKS2NS(now + delay));
hrtimer_start(&q->delay_timer, time, HRTIMER_MODE_ABS);
}
sch->flags &= ~TCQ_F_THROTTLED;
__netif_schedule(qdisc_root(sch));
return HRTIMER_NORESTART;
}
#ifdef CONFIG_NET_CLS_ACT
static int cbq_reshape_fail(struct sk_buff *skb, struct Qdisc *child)
{
struct Qdisc *sch = child->__parent;
struct cbq_sched_data *q = qdisc_priv(sch);
struct cbq_class *cl = q->rx_class;
q->rx_class = NULL;
if (cl && (cl = cbq_reclassify(skb, cl)) != NULL) {
int ret;
cbq_mark_toplevel(q, cl);
q->rx_class = cl;
cl->q->__parent = sch;
ret = qdisc_enqueue(skb, cl->q);
if (ret == NET_XMIT_SUCCESS) {
sch->q.qlen++;
sch->bstats.packets++;
sch->bstats.bytes += qdisc_pkt_len(skb);
if (!cl->next_alive)
cbq_activate_class(cl);
return 0;
}
if (net_xmit_drop_count(ret))
sch->qstats.drops++;
return 0;
}
sch->qstats.drops++;
return -1;
}
#endif
/*
It is mission critical procedure.
We "regenerate" toplevel cutoff, if transmitting class
has backlog and it is not regulated. It is not part of
original CBQ description, but looks more reasonable.
Probably, it is wrong. This question needs further investigation.
*/
static __inline__ void
cbq_update_toplevel(struct cbq_sched_data *q, struct cbq_class *cl,
struct cbq_class *borrowed)
{
if (cl && q->toplevel >= borrowed->level) {
if (cl->q->q.qlen > 1) {
do {
if (borrowed->undertime == PSCHED_PASTPERFECT) {
q->toplevel = borrowed->level;
return;
}
} while ((borrowed=borrowed->borrow) != NULL);
}
#if 0
/* It is not necessary now. Uncommenting it
will save CPU cycles, but decrease fairness.
*/
q->toplevel = TC_CBQ_MAXLEVEL;
#endif
}
}
static void
cbq_update(struct cbq_sched_data *q)
{
struct cbq_class *this = q->tx_class;
struct cbq_class *cl = this;
int len = q->tx_len;
q->tx_class = NULL;
for ( ; cl; cl = cl->share) {
long avgidle = cl->avgidle;
long idle;
cl->bstats.packets++;
cl->bstats.bytes += len;
/*
(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 = q->now - cl->last;
if ((unsigned long)idle > 128*1024*1024) {
avgidle = cl->maxidle;
} else {
idle -= L2T(cl, len);
/* true_avgidle := (1-W)*true_avgidle + W*idle,
where W=2^{-ewma_log}. But cl->avgidle is scaled:
cl->avgidle == true_avgidle/W,
hence:
*/
avgidle += idle - (avgidle>>cl->ewma_log);
}
if (avgidle <= 0) {
/* Overlimit or at-limit */
if (avgidle < cl->minidle)
avgidle = cl->minidle;
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);
*/
idle = (-avgidle) - ((-avgidle) >> cl->ewma_log);
/*
That is not all.
To maintain the rate allocated to the class,
we add to undertime virtual clock,
necessary to complete transmitted packet.
(len/phys_bandwidth has been already passed
to the moment of cbq_update)
*/
idle -= L2T(&q->link, len);
idle += L2T(cl, len);
cl->undertime = q->now + idle;
} else {
/* Underlimit */
cl->undertime = PSCHED_PASTPERFECT;
if (avgidle > cl->maxidle)
cl->avgidle = cl->maxidle;
else
cl->avgidle = avgidle;
}
cl->last = q->now;
}
cbq_update_toplevel(q, this, q->tx_borrowed);
}
static __inline__ struct cbq_class *
cbq_under_limit(struct cbq_class *cl)
{
struct cbq_sched_data *q = qdisc_priv(cl->qdisc);
struct cbq_class *this_cl = cl;
if (cl->tparent == NULL)
return cl;
if (cl->undertime == PSCHED_PASTPERFECT || q->now >= cl->undertime) {
cl->delayed = 0;
return cl;
}
do {
/* It is very suspicious place. Now overlimit
action is generated for not bounded classes
only if link is completely congested.
Though it is in agree with ancestor-only paradigm,
it looks very stupid. Particularly,
it means that this chunk of code will either
never be called or result in strong amplification
of burstiness. Dangerous, silly, and, however,
no another solution exists.
*/
if ((cl = cl->borrow) == NULL) {
this_cl->qstats.overlimits++;
this_cl->overlimit(this_cl);
return NULL;
}
if (cl->level > q->toplevel)
return NULL;
} while (cl->undertime != PSCHED_PASTPERFECT && q->now < cl->undertime);
cl->delayed = 0;
return cl;
}
static __inline__ struct sk_buff *
cbq_dequeue_prio(struct Qdisc *sch, int prio)
{
struct cbq_sched_data *q = qdisc_priv(sch);
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 {
struct cbq_class *borrow = cl;
if (cl->q->q.qlen &&
(borrow = cbq_under_limit(cl)) == NULL)
goto skip_class;
if (cl->deficit <= 0) {
/* Class exhausted its allotment per
this round. Switch to the next one.
*/
deficit = 1;
cl->deficit += cl->quantum;
goto next_class;
}
skb = cl->q->dequeue(cl->q);
/* Class did not give us any skb :-(
It could occur even if cl->q->q.qlen != 0
f.e. if cl->q == "tbf"
*/
if (skb == NULL)
goto skip_class;
cl->deficit -= qdisc_pkt_len(skb);
q->tx_class = cl;
q->tx_borrowed = borrow;
if (borrow != cl) {
#ifndef CBQ_XSTATS_BORROWS_BYTES
borrow->xstats.borrows++;
cl->xstats.borrows++;
#else
borrow->xstats.borrows += qdisc_pkt_len(skb);
cl->xstats.borrows += qdisc_pkt_len(skb);
#endif
}
q->tx_len = qdisc_pkt_len(skb);
if (cl->deficit <= 0) {
q->active[prio] = cl;
cl = cl->next_alive;
cl->deficit += cl->quantum;
}
return skb;
skip_class:
if (cl->q->q.qlen == 0 || prio != cl->cpriority) {
/* Class is empty or penalized.
Unlink it from active chain.
*/
cl_prev->next_alive = cl->next_alive;
cl->next_alive = NULL;
/* 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);
if (cl->q->q.qlen)
cbq_activate_class(cl);
return NULL;
}
q->active[prio] = cl_tail;
}
if (cl->q->q.qlen)
cbq_activate_class(cl);
cl = cl_prev;
}
next_class:
cl_prev = cl;
cl = cl->next_alive;
} 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)
{
struct cbq_sched_data *q = qdisc_priv(sch);
struct sk_buff *skb;
unsigned activemask;
activemask = q->activemask&0xFF;
while (activemask) {
int prio = ffz(~activemask);
activemask &= ~(1<<prio);
skb = cbq_dequeue_prio(sch, prio);
if (skb)
return skb;
}
return NULL;
}
static struct sk_buff *
cbq_dequeue(struct Qdisc *sch)
{
struct sk_buff *skb;
struct cbq_sched_data *q = qdisc_priv(sch);
psched_time_t now;
psched_tdiff_t incr;
now = psched_get_time();
incr = now - q->now_rt;
if (q->tx_class) {
psched_tdiff_t incr2;
/* Time integrator. We calculate EOS time
by adding expected packet transmission time.
If real time is greater, we warp artificial clock,
so that:
cbq_time = max(real_time, work);
*/
incr2 = L2T(&q->link, q->tx_len);
q->now += incr2;
cbq_update(q);
if ((incr -= incr2) < 0)
incr = 0;
}
q->now += incr;
q->now_rt = now;
for (;;) {
q->wd_expires = 0;
skb = cbq_dequeue_1(sch);
if (skb) {
sch->q.qlen--;
sch->flags &= ~TCQ_F_THROTTLED;
return skb;
}
/* All the classes are overlimit.
It is possible, if:
1. Scheduler is empty.
2. Toplevel cutoff inhibited borrowing.
3. Root class is overlimit.
Reset 2d and 3d conditions and retry.
Note, that NS and cbq-2.0 are buggy, peeking
an arbitrary class is appropriate for ancestor-only
sharing, but not for toplevel algorithm.
Our version is better, but slower, because it requires
two passes, but it is unavoidable with top-level sharing.
*/
if (q->toplevel == TC_CBQ_MAXLEVEL &&
q->link.undertime == PSCHED_PASTPERFECT)
break;