后端 rs 一般有多个，通过一定算法做负载均衡。程序初始化时 dp_vs_init 调用 dp_vs_sched_init 进行全局注册。
int dp_vs_sched_init(void)
{
INIT_LIST_HEAD(&dp_vs_schedulers);
rte_rwlock_init(&__dp_vs_sched_lock);
dp_vs_rr_init();
dp_vs_wrr_init();
dp_vs_wlc_init();
dp_vs_conhash_init();
return EDPVS_OK;
}
可以看到 dpvs 当前支持 rr, wrr, wlc, conhash 四种调度算法。
调度入口
当 client 首次请求时，dp_vs_schedule 选择 rs，然后建立连接
dest = svc->scheduler->schedule(svc, mbuf);
这就是调度入口，具体使用哪种算法，由程序初始化时，配置 service 服务时决定。dp_vs_bind_scheduler 调用 scheduler->init_service 函数指针初始化。
轮循算法 rr
首先这是最简单的算法，看下如何实现的。首先看 init_service 初始化函数
static int dp_vs_rr_init_svc(struct dp_vs_service *svc)
{
svc->sched_data = &svc->dests;
return EDPVS_OK;
}
很简单，直接将后端 rs 链表 dests 赋给 sched_data. 再看一下 schedule 入口
static struct dp_vs_dest *dp_vs_rr_schedule(struct dp_vs_service *svc,
const struct rte_mbuf *mbuf)
{
struct list_head *p, *q;
struct dp_vs_dest *dest;
rte_rwlock_write_lock(&svc->sched_lock);
p = (struct list_head *)svc->sched_data;
p = p->next;
q = p;
do {
/* skip list head */
if (q == &svc->dests) {
q = q->next;
continue;
}
dest = list_entry(q, struct dp_vs_dest, n_list);
if (!(dest->flags & DPVS_DEST_F_OVERLOAD) &&
(dest->flags & DPVS_DEST_F_AVAILABLE) &&
rte_atomic16_read(&dest->weight) > 0)
/* HIT */
goto out;
q = q->next;
} while (q != p);
rte_rwlock_write_unlock(&svc->sched_lock);
return NULL;
out:
svc->sched_data = q;
rte_rwlock_write_unlock(&svc->sched_lock);
return dest;
}
原理也很明了，遍历 sched_data 链表，找到第一个可用的 dest 后返回，并保存找到的位置，下次选择时从这个位置的下一个开始查找。
加权轮循 wrr
带权重的轮循，首先看 init_service 初始化函数
static int dp_vs_wrr_init_svc(struct dp_vs_service *svc)
{
struct dp_vs_wrr_mark *mark;
/*
* Allocate the mark variable for WRR scheduling
*/
mark = rte_zmalloc("wrr_mark", sizeof(struct dp_vs_wrr_mark), RTE_CACHE_LINE_SIZE);
if (mark == NULL) {
return EDPVS_NOMEM;
}
mark->cl = &svc->dests;
mark->cw = 0;
mark->mw = dp_vs_wrr_max_weight(svc);
mark->di = dp_vs_wrr_gcd_weight(svc);
svc->sched_data = mark;
return EDPVS_OK;
}
struct dp_vs_wrr_mark {
struct list_head *cl; /* current list head */
int cw; /* current weight */
int mw; /* maximum weight */
int di; /* decreasing interval */
};
分配 dp_vs_wrr_mark 结构体，初始化赋值给 svc->sched_data. dp_vs_wrr_max_weight 求出后端 rs 权重最大值，dp_vs_wrr_gcd_weight 求出这些权重值的最大公约数，这个 gcd 用于权重值增减的步长。比如权重分别是 100，20，50，那么 gcd 就是 10，所谓的 decreasing interval 就是 10.
static struct dp_vs_dest *dp_vs_wrr_schedule(struct dp_vs_service *svc,
const struct rte_mbuf *mbuf)
{
struct dp_vs_dest *dest;
struct dp_vs_wrr_mark *mark = svc->sched_data;
struct list_head *p;
/*
* This loop will always terminate, because mark->cw in (0, max_weight]
* and at least one server has its weight equal to max_weight.
*/
rte_rwlock_write_lock(&svc->sched_lock);
p = mark->cl;
while (1) {
if (mark->cl == &svc->dests) {
/* it is at the head of the destination list */
if (mark->cl == mark->cl->next) {
/* no dest entry */
dest = NULL;
goto out;
}
mark->cl = svc->dests.next;
mark->cw -= mark->di;
if (mark->cw <= 0) {
mark->cw = mark->mw;
/*
* Still zero, which means no available servers.
*/
if (mark->cw == 0) {
mark->cl = &svc->dests;
dest = NULL;
goto out;
}
}
} else
mark->cl = mark->cl->next;
if (mark->cl != &svc->dests) {
/* not at the head of the list */
dest = list_entry(mark->cl, struct dp_vs_dest, n_list);
if (!(dest->flags & DPVS_DEST_F_OVERLOAD) &&
(dest->flags & DPVS_DEST_F_AVAILABLE) &&
rte_atomic16_read(&dest->weight) >= mark->cw) {
/* got it */
break;
}
}
if (mark->cl == p && mark->cw == mark->di) {
/* back to the start, and no dest is found.
It is only possible when all dests are OVERLOADED */
dest = NULL;
goto out;
}
}
out:
rte_rwlock_write_unlock(&svc->sched_lock);
return dest;
}
- 首次循环 mark->cl = &svc->dests, 也就是队首，cw 减去一个步长 di. 并且将 mark->cl 置为队首后的第一个元素 svc->dests.next 然后查看 mark->cl 的权重如果大于 cw, 那么返回当前 mark->cl 做为 rs.
- 如果此时 mark->cl 不是队首，那么直接
mark->cl = mark->cl->next查看下一个元素，是否满足可用，并且权重大于 cw, 符合要求返回 mark->cl 做为 rs - 如果mark->cl 权重小于 cw, 那么 while 循环，继续遍历下一个。
这个算法的原理清楚了，但是 while 循环的复杂度暂时不知道，水平有限...
加权最小连接 wlc
static struct dp_vs_scheduler dp_vs_wlc_scheduler = {
.name = "wlc",
.n_list = LIST_HEAD_INIT(dp_vs_wlc_scheduler.n_list),
.schedule = dp_vs_wlc_schedule,
};
这个调度算法是没有 init_service 函数的，那么直接看 dp_vs_wlc_schedule
static struct dp_vs_dest *dp_vs_wlc_schedule(struct dp_vs_service *svc,
const struct rte_mbuf *mbuf)
{
struct dp_vs_dest *dest, *least;
unsigned int loh, doh;
/*
* We calculate the load of each dest server as follows:
* (dest overhead) / dest->weight
*
* The server with weight=0 is quiesced and will not receive any
* new connections.
*/
list_for_each_entry(dest, &svc->dests, n_list) {
if (!(dest->flags & DPVS_DEST_F_OVERLOAD) &&
(dest->flags & DPVS_DEST_F_AVAILABLE) &&
rte_atomic16_read(&dest->weight) > 0) {
least = dest;
loh = dp_vs_wlc_dest_overhead(least);
goto nextstage;
}
}
return NULL;
/*
* Find the destination with the least load.
*/
nextstage:
list_for_each_entry_continue(dest, &svc->dests, n_list) {
if (dest->flags & DPVS_DEST_F_OVERLOAD)
continue;
doh = dp_vs_wlc_dest_overhead(dest);
if (loh * rte_atomic16_read(&dest->weight) >
doh * rte_atomic16_read(&least->weight)) {
least = dest;
loh = doh;
}
}
return least;
}
static inline unsigned int dp_vs_wlc_dest_overhead(struct dp_vs_dest *dest)
{
return (rte_atomic32_read(&dest->actconns) << 8) +
rte_atomic32_read(&dest->inactconns);
}
- 首先是给后端 rs 打分的算法, (dest overhead) / dest->weight，负载除以权重。负载是由
dp_vs_wlc_dest_overhead完成计算，活跃连接和非活跃连接的加权统计，活跃占比最大。那么这个打分，肯定是越小，被选择的可能性越大 - 第一个 list_for_each_entry，找出第一个 rs, 算出打分。第二个遍历所有 rs, 将打分进行对比，最后分最少的被赋值 least, 返回给上游使用。
连接哈希 conhash
这个算法用的好像不多，会将相同 hash 算法的固定分配置某个后端 rs. 先看 init_service
static int dp_vs_conhash_init_svc(struct dp_vs_service *svc)
{
svc->sched_data = conhash_init(NULL);
if (!svc->sched_data) {
RTE_LOG(ERR, SERVICE, "%s: conhash init faild!\n", __func__);
return EDPVS_NOMEM;
}
dp_vs_conhash_assign(svc);
return EDPVS_OK;
}
这块 conhash_init 居然用了红黑树的实现，然后调用 dp_vs_conhash_assign 将后端 rs hash 到这个 rbtree 里.
static int
dp_vs_conhash_assign(struct dp_vs_service *svc)
{
struct dp_vs_dest *dest;
struct node_s *p_node;
int weight = 0;
char str[40];
list_for_each_entry(dest, &svc->dests, n_list) {
weight = rte_atomic16_read(&dest->weight);
if (weight > 0) {
p_node = rte_zmalloc("p_node", sizeof(struct node_s), RTE_CACHE_LINE_SIZE);
if (p_node == NULL) {
return EDPVS_NOMEM;
}
rte_atomic32_inc(&dest->refcnt);
p_node->data = dest;
snprintf(str, sizeof(str), "%u%d", dest->addr.in.s_addr, dest->port);
conhash_set_node(p_node, str, weight*REPLICA);
conhash_add_node(svc->sched_data, p_node);
}
}
return EDPVS_OK;
}
- 只有 weight 大于 0 才是可用的 rs
- 生成 node 节点加入到树里，这里看节点分复制成 weightREPLICA 份，做一致性 hash 用，建了 权重160个虚拟节点
static struct dp_vs_dest *
dp_vs_conhash_schedule(struct dp_vs_service *svc, const struct rte_mbuf *mbuf)
{
struct dp_vs_dest *dest;
dest = dp_vs_conhash_get(svc, (struct conhash_s *)svc->sched_data, mbuf);
if (!dest
|| !(dest->flags & DPVS_DEST_F_AVAILABLE)
|| rte_atomic16_read(&dest->weight) <= 0
|| is_overloaded(dest)) {
return NULL;
}
else
return dest;
}
schedule 函数也不难，直接根据 mbuf 调用 dp_vs_conhash_get, 获取最近的虚拟节点即可。
static inline struct dp_vs_dest *
dp_vs_conhash_get(struct dp_vs_service *svc, struct conhash_s *conhash,
const struct rte_mbuf *mbuf)
{
char str[40] = {0};
uint64_t quic_cid;
uint32_t sip;
const struct node_s *node;
if (svc->flags & DP_VS_SVC_F_QID_HASH) {
if (svc->proto != IPPROTO_UDP) {
RTE_LOG(ERR, IPVS, "QUIC cid hash scheduler should only be set in UDP service.\n");
return NULL;
}
/* try to get CID for hash target first, then source IP. */
if (EDPVS_OK == get_quic_hash_target(mbuf, &quic_cid)) {
snprintf(str, sizeof(str), "%lu", quic_cid);
} else if (EDPVS_OK == get_sip_hash_target(mbuf, &sip)) {
snprintf(str, sizeof(str), "%u", sip);
} else {
return NULL;
}
} else if (svc->flags & DP_VS_SVC_F_SIP_HASH) {
if (EDPVS_OK == get_sip_hash_target(mbuf, &sip)) {
snprintf(str, sizeof(str), "%u", sip);
} else {
return NULL;
}
} else {
RTE_LOG(ERR, IPVS, "%s: invalid hash target.\n", __func__);
return NULL;
}
node = conhash_lookup(conhash, str);
return node == NULL? NULL: node->data;
}
可以看到，对于 udp 如果如果开启了 CID，那么调用 get_quic_hash_target 生成 hash 值。其它情况一律使用 get_sip_hash_target 即源地址 ip 生成 hash
总结
这块比较常见，也没什么难度，大家看看就好
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