Linux内核中流量控制(14)
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5.14 CBQ(Class Based Queueing, 基于类别的排队)CBQ(Class-Based Queueing discipline)是个经典的基于分类的流控算法，比较复杂, 具体算法基础也是TBF, 也是根据令牌情况决定是否发送数据包。CBQ在HTB出现后一般用得就少了, 其实对于分类的类别操作和HTB也差不多, 所以只简要介绍一下入队和出队操作过程, 其他处理过程不再详细分析了。
5.14.1 CBQ相关结构定义
// CBQ流控结构
static struct Qdisc_ops cbq_qdisc_ops = {
.next = NULL,
.cl_ops = &cbq_class_ops,
.id = "cbq",
// 私有数据是一个用于CBQ调度的数据结构struct cbq_sched_data
.priv_size = sizeof(struct cbq_sched_data),
.enqueue = cbq_enqueue,
.dequeue = cbq_dequeue,
.requeue = cbq_requeue,
.drop = cbq_drop,
.init = cbq_init,
.reset = cbq_reset,
.destroy = cbq_destroy,
.change = NULL,
.dump = cbq_dump,
.dump_stats = cbq_dump_stats,
.owner = THIS_MODULE,
};// CBQ类别操作结构
static struct Qdisc_class_ops cbq_class_ops = {
.graft = cbq_graft,
.leaf = cbq_leaf,
.get = cbq_get,
.put = cbq_put,
.change = cbq_change_class,
.delete = cbq_delete,
.walk = cbq_walk,
.tcf_chain = cbq_find_tcf,
.bind_tcf = cbq_bind_filter,
.unbind_tcf = cbq_unbind_filter,
.dump = cbq_dump_class,
.dump_stats = cbq_dump_class_stats,
};// CBQ调度数据, 是作为CBQ调度算法的Qdisc的私有数据
struct cbq_sched_data
{
// 类别HASH表, 16个链表
struct cbq_class *classes[16]; /* Hash table of all classes */
int nclasses[TC_CBQ_MAXPRIO+1];
unsigned quanta[TC_CBQ_MAXPRIO+1];
struct cbq_class link;
unsigned activemask;
// 活动的CBQ类别链表, 最多8+1个, 按类别优先权区分
struct cbq_class *active[TC_CBQ_MAXPRIO+1]; /* List of all classes
with backlog */
#ifdef CONFIG_NET_CLS_POLICE
// 接收用的CBQ类别结构
struct cbq_class *rx_class;
#endif
// 发送用的CBQ类别结构
struct cbq_class *tx_class;
// 借带宽时的CBQ类别结构
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 timer_list delay_timer;
struct timer_list wd_timer; /* Watchdog timer,
started when CBQ has
backlog, but cannot
transmit just now */
long wd_expires;
int toplevel;
u32 hgenerator;
};// CBQ类别结构
struct cbq_class
{
// 链表下一项
struct cbq_class *next; /* hash table link */
// backlog中的下一个活动的类别结构
struct cbq_class *next_alive; /* next class with backlog in this priority band */
/* Parameters */
// 类型ID值
u32 classid;
// 正常情况下的优先权值
unsigned char priority; /* class priority */
// 流量超过限制值后使用的优先权值
unsigned char priority2; /* priority to be used after overlimit */
//
unsigned char ewma_log; /* time constant for idle time calculation */
// ovl策略
unsigned char ovl_strategy;
#ifdef CONFIG_NET_CLS_POLICE
unsigned char police;
#endif
// 缺省
u32 defmap;
/* Link-sharing scheduler parameters */
long maxidle; /* Class parameters: see below. */
long offtime;
long minidle;
u32 avpkt;
// 流量表指针
struct qdisc_rate_table *R_tab;
/* Overlimit strategy parameters */
// 超过限制时的处理函数
void (*overlimit)(struct cbq_class *cl);
long penalty;
/* General scheduler (WRR) parameters */
long allot;
long quantum; /* Allotment per WRR round */
long weight; /* Relative allotment: see below */
// 指向当前Qdisc结构
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 */
// 内部流控节点, 实际通过该Qdisc完成流控操作
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_
