linux网络流控-htb算法简析

tc qdisc add dev eth0 root handle 1: htb
tc class add dev eth0 parent 1:  classid 1:1  htb rate 100mibps
tc class add dev eth0 parent 1:1 classid 1:10 htb rate 30mibps ceil 80mibps prio 0 burst 10kbit cburst 20kbit quantum 30000
tc class add dev eth0 parent 1:1 classid 1:20 htb rate 20mibps ceil 50mibps prio 1 burst 10kbit cburst 20kbit quantum 20000
tc class add dev eth0 parent 1:10 classid 1:101 htb rate 10mibps ceil 80mibps prio 1 burst 10kbit cburst 20kbit quantum 10000
tc class add dev eth0 parent 1:10 classid 1:102 htb rate 5mibps ceil 40mibps prio 0 burst 10kbit cburst 20kbit quantum 5000

iptables -t mangle -A OUTPUT -d 192.168.1.2 -j CLASSIFY --set-class 1:20
iptables -t mangle -A OUTPUT -d 192.168.1.3 -j CLASSIFY --set-class 1:101
iptables -t mangle -A OUTPUT -d 192.168.1.4 -j CLASSIFY --set-class 1:10

static struct sk_buff *htb_dequeue(struct Qdisc *sch)
{
    ...
    for(level = 0; level < TC_HTB_MAXDEPTH; level++) {   // 逐层找.这里level是反的,0层表示最底层.
        /* common case optimization - skip event handler quickly */
        int m;
        ...
        m = ~q->row_mask[level];
        while(m !=(int)(-1)) {        // 同一层取优先级高的
            int prio = ffz(m);
            m |= 1 << prio;
            skb = htb_dequeue_tree(q, prio, level);   //出包
            if(likely(skb != NULL)) {
                sch->q.qlen--;
                sch->flags &= ~TCQ_F_THROTTLED;
                goto fin;
            }
        }
    }
    sch->qstats.overlimits++;
    ...
fin:
    return skb;
}

static struct sk_buff *htb_dequeue_tree(struct htb_sched *q, int prio, int level)
{
    struct sk_buff *skb = NULL;
    struct htb_class *cl, *start;
    ...
    cl = htb_lookup_leaf(q->row[level] + prio,prio, q->ptr[level] + prio,  // 找到该level 该priority下的一个leafclass
                   q->last_ptr_id[level] + prio);

    skb = cl->un.leaf.q->dequeue(cl->un.leaf.q);     // 出包

    if(likely(skb != NULL)) {
        cl->un.leaf.deficit[level] -= qdisc_pkt_len(skb);  //deficit[level] 扣掉该包的byte数
        if(cl->un.leaf.deficit[level] < 0) {              //当deficit[level]<0时说明该类已经发送了quantum.需要发送下一个类了.
            cl->un.leaf.deficit[level] += cl->quantum;
            htb_next_rb_node((level ? cl->parent->un.inner.ptr : q->
                      ptr[0]) + prio);
        }
        htb_charge_class(q, cl, level, skb);    // 更新令牌.
    }
    return skb;
}

static void htb_charge_class(struct htb_sched *q, struct htb_class *cl,int level, struct sk_buff *skb)
{
    int bytes = qdisc_pkt_len(skb);
    enum htb_cmode old_mode;
    long diff;

    while(cl) {        //这里是一个循环,子类发包,是同时要扣子类和父类的令牌的.
        diff = psched_tdiff_bounded(q->now, cl->t_c, cl->mbuffer);
        if(cl->level >= level) {
            if(cl->level == level)         //令牌的生产,扣减在这里.
                cl->xstats.lends++;
            htb_accnt_tokens(cl, bytes, diff);
        } else {
            cl->xstats.borrows++;
            cl->tokens += diff; /* we moved t_c; update tokens */
        }
        htb_accnt_ctokens(cl, bytes, diff);
        cl->t_c = q->now;

        old_mode = cl->cmode;
        diff = 0;
        htb_change_class_mode(q, cl, &diff);        //判断是不是要切换状态了.
        if(old_mode != cl->cmode) {
            if(old_mode != HTB_CAN_SEND)
                htb_safe_rb_erase(&cl->pq_node, q->wait_pq + cl->level);
            if(cl->cmode != HTB_CAN_SEND)
                htb_add_to_wait_tree(q, cl, diff);
        }
        cl = cl->parent;
    }
}