Copilot commented on code in PR #3526:
URL: https://github.com/apache/brpc/pull/3526#discussion_r3952290721
##########
docs/cn/client.md:
##########
@@ -290,6 +290,14 @@ locality-aware，优先选择延时低的下游，直到其延时高于其他机
channel.Init("http://...";, "random:min_working_instances=6 hold_seconds=10",
&options);
```
+### 慢启动（预热）
+
+新加入集群或刚重启的server往往是“冷”的（缓存未命中、JIT未编译、连接池未建立），立即承担全量流量会推高其延时甚至过载。设置-lb_warmup_ms大于0（默认为0，即关闭）后，新加入负载均衡器的server先获得一小部分正常流量份额（-lb_warmup_min_weight，默认0.1），并在该时间窗口内线性爬升到100%。该机制对rr、wrr、random、la、p2c和一致性哈希均生效：la和p2c把爬升系数乘入权重，与延时评分自然叠加而不会互相干扰；其余算法按该系数概率性地把请求转给其他server（一致性哈希转给环上的下一个节点，预热期间会有部分请求偏离原有的哈希亲和性）。
Review Comment:
这里写“线性爬升到100%”与下一段 -lb_warmup_curve 可配置曲线的描述不一致（曲线 != 1
时并非线性）。建议去掉“线性”或改成更泛化的表述。
##########
src/brpc/load_balancer.h:
##########
@@ -113,6 +113,31 @@ class LoadBalancer : public NonConstDescribable, public
Destroyable {
DECLARE_bool(show_lb_in_vars);
DECLARE_int32(default_weight_of_wlb);
+DECLARE_int64(lb_warmup_ms);
+
+double WarmupMultiplierImpl(int64_t join_time_us, int64_t now_us);
+bool WarmupAcceptImpl(int64_t join_time_us, int64_t now_us);
+
+// Slow start: while -lb_warmup_ms is positive, a server newly added to a
+// LoadBalancer serves a ramping fraction of its normal traffic share, from
+// about 10% right after joining to 100% at the end of the window. The ramp
+// restarts when a removed server is added back(naming service flap); a
+// transiently disconnected server does not change LB membership and keeps
+// its ramp. Servers added together(e.g. at channel init) ramp together and
+// keep their relative shares.
+// Returns the weight multiplier in (0, 1] for a server that joined the
+// LoadBalancer at `join_time_us'(gettimeofday_us). `now_us' <= 0 makes the
+// function read the clock itself.
+inline double WarmupMultiplier(int64_t join_time_us, int64_t now_us) {
+ return FLAGS_lb_warmup_ms <= 0 ?
+ 1.0 : WarmupMultiplierImpl(join_time_us, now_us);
+}
+
+// Probabilistic form of WarmupMultiplier for policies without changable
+// weights: returns true with probability WarmupMultiplier(...).
Review Comment:
Typo in the comment: “changable” should be “changeable”.
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