cregit-Linux how code gets into the kernel

Release 4.8 net/sched/sch_cbq.c

Directory: net/sched
/*
 * 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 <linux/module.h>
#include <linux/slab.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 */

	
u32			defmap;

	/* Link-sharing scheduler parameters */
	
long			maxidle;	/* Class parameters: see below. */
	
long			offtime;
	
long			minidle;
	
u32			avpkt;
	
struct qdisc_rate_table	*R_tab;

	/* 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_est64 rate_est;
	
struct tc_cbq_xstats	xstats;

	
struct tcf_proto __rcu	*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 int		quanta[TC_CBQ_MAXPRIO + 1];

	
struct cbq_class	link;

	
unsigned int		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 */
	
unsigned int		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); }

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#ifdef CONFIG_NET_CLS_ACT
static struct cbq_class * cbq_reclassify(struct sk_buff *skb, struct cbq_class *this) { struct cbq_class *cl; for (cl = this->tparent; cl; cl = cl->tparent) { struct cbq_class *new = cl->defaults[TC_PRIO_BESTEFFORT]; if (new != NULL && new != this) return new; } return NULL; }

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#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_proto *fl; 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; fl = rcu_dereference_bh(head->filter_list); /* * Step 2+n. Apply classifier. */ result = tc_classify(skb, fl, &res, true); if (!fl || result < 0) goto fallback; cl = (void *)res.class; if (!cl) { 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) goto fallback; } if (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; }

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patrick mchardypatrick mchardy205.70%214.29%
eric dumazeteric dumazet123.42%214.29%
jarek poplawskijarek poplawski51.42%214.29%
stephen hemmingerstephen hemminger30.85%17.14%
daniel borkmanndaniel borkmann30.85%17.14%
Total351100.00%14100.00%

/* * 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); } }

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/* * 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]); }

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static void cbq_mark_toplevel(struct cbq_sched_data *q, struct cbq_class *cl) { int toplevel = q->toplevel; if (toplevel > cl->level) { psched_time_t now = psched_get_time(); do { if (cl->undertime < now) { q->toplevel = cl->level; return; } } while ((cl = cl->borrow) != NULL && toplevel > cl->level); } }

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static int cbq_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free) { 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) qdisc_qstats_drop(sch); __qdisc_drop(skb, to_free); return ret; } ret = qdisc_enqueue(skb, cl->q, to_free); if (ret == NET_XMIT_SUCCESS) { sch->q.qlen++; cbq_mark_toplevel(q, cl); if (!cl->next_alive) cbq_activate_class(cl); return ret; } if (net_xmit_drop_count(ret)) { qdisc_qstats_drop(sch); cbq_mark_toplevel(q, cl); cl->qstats.drops++; } return ret; }

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eric dumazeteric dumazet116.32%16.25%
jarek poplawskijarek poplawski116.32%212.50%
john fastabendjohn fastabend63.45%16.25%
jussi kivilinnajussi kivilinna52.87%16.25%
stephen hemmingerstephen hemminger31.72%16.25%
satyam sharmasatyam sharma31.72%16.25%
thomas grafthomas graf10.57%16.25%
Total174100.00%16100.00%

/* Overlimit action: penalize leaf class by adding offtime */
static void cbq_overlimit(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; } }

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eric dumazeteric dumazet10.43%114.29%
Total230100.00%7100.00%


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; }

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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 int 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_PINNED); } __netif_schedule(qdisc_root(sch)); return HRTIMER_NORESTART; }

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eric dumazeteric dumazet21.05%218.18%
jarek poplawskijarek poplawski10.53%19.09%
Total190100.00%11100.00%

/* * 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 } }

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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; psched_time_t now; q->tx_class = NULL; /* Time integrator. We calculate EOS time * by adding expected packet transmission time. */ now = q->now + L2T(&q->link, len); 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 = 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 = now + idle; } else { /* Underlimit */ cl->undertime = PSCHED_PASTPERFECT; if (avgidle > cl->maxidle) cl->avgidle = cl->maxidle; else cl->avgidle = avgidle; } if ((s64)(now - cl->last) > 0) cl->last = now; } cbq_update_toplevel(q, this, q->tx_borrowed); }

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thomas grafthomas graf20.67%111.11%
Total297100.00%9100.00%


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. */ cl = cl->borrow; if (!cl) { this_cl->qstats.overlimits++; cbq_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; }

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stephen hemmingerstephen hemminger32.11%112.50%
thomas grafthomas graf10.70%112.50%
florian westphalflorian westphal10.70%112.50%
Total142100.00%8100.00%


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; }

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stephen hemmingerstephen hemminger30.69%116.67%
Total434100.00%6100.00%


static inline struct sk_buff * cbq_dequeue_1(struct Qdisc *sch) { struct cbq_sched_data *q = qdisc_priv(sch); struct sk_buff *skb; unsigned int 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; }

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stephen hemmingerstephen hemminger33.57%133.33%
Total84100.00%3100.00%


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; now = psched_get_time(); if (q->tx_class) cbq_update(q); q->now = now; for (;;) { q->wd_expires = 0; skb = cbq_dequeue_1(sch); if (skb) { qdisc_bstats_update(sch, skb); sch->q.qlen--; 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; q->toplevel = TC_CBQ_MAXLEVEL; q->link.undertime = PSCHED_PASTPERFECT; } /* No packets in scheduler or nobody wants to give them to us :-( * Sigh... start watchdog timer in the last case. */ if (sch->q.qlen) { qdisc_qstats_overlimit(sch); if (q->wd_expires) qdisc_watchdog_schedule(