[PD] Optimize time out logic and add env var doc for mooncake (#6761)

Signed-off-by: Shangming Cai <caishangming@linux.alibaba.com>

docs/backend/pd_disaggregation.md

@@ -47,6 +47,23 @@ $ python -m sglang.launch_server --model-path deepseek-ai/DeepSeek-V3-0324 --dis
 # decode 1
 $ python -m sglang.launch_server --model-path deepseek-ai/DeepSeek-V3-0324 --disaggregation-ib-device ${device_name} --disaggregation-mode decode --host ${local_ip} --port 30001 --trust-remote-code --dist-init-addr ${decode_master_ip}:5000 --nnodes 2 --node-rank 1 --tp-size 16 --dp-size 8 --enable-dp-attention --enable-deepep-moe --deepep-mode low_latency --mem-fraction-static 0.8 --max-running-requests 128
 ```
+### Advanced Configuration
+
+PD Disaggregation with Mooncake supports the following environment variables for fine-grained control over system behavior.
+
+#### Prefill Server Configuration
+| Variable | Description | Default |
+|:--------:|:-----------:|:--------:
+| **`SGLANG_DISAGGREGATION_THREAD_POOL_SIZE`** | Controls the total number of worker threads for KV transfer operations per TP rank | A dynamic value calculated by `int(0.75 * os.cpu_count()) // 8)`, which is limited to be larger than 4 and less than 12 to ensure efficiency and prevent thread race conditions |
+| **`SGLANG_DISAGGREGATION_QUEUE_SIZE`** | Sets the maximum pending tasks in the parallel transfer queue | `4` |
+| **`SGLANG_DISAGGREGATION_BOOTSTRAP_TIMEOUT`** | Timeout (seconds) for receiving destination KV indices during request initialization | `30` |
+
+#### Decode Server Configuration
+| Variable | Description | Default |
+|:--------:|:-----------:|:--------:
+| **`SGLANG_DISAGGREGATION_HEARTBEAT_INTERVAL`** | Interval (seconds) between health checks to prefill bootstrap servers | `5.0` |
+| **`SGLANG_DISAGGREGATION_HEARTBEAT_MAX_FAILURE`** | Consecutive heartbeat failures before marking prefill server offline | `2` |
+
 
 ## NIXL
 ### Requirements

python/sglang/srt/disaggregation/mooncake/conn.py

@@ -677,14 +677,15 @@ class MooncakeKVSender(BaseKVSender):
         self.kv_mgr.update_status(bootstrap_room, KVPoll.Bootstrapping)
         self.aux_index = None
         self.bootstrap_server_url = bootstrap_addr
-        self.init_time = time.time()
         self.conclude_state = None
+        self.init_time = None
         # inner state
         self.curr_idx = 0
 
     def init(self, num_kv_indices: int, aux_index: Optional[int] = None):
         self.num_kv_indices = num_kv_indices
         self.aux_index = aux_index
+        self.init_time = time.time()
 
     def send(
         self,
@@ -713,15 +714,16 @@ class MooncakeKVSender(BaseKVSender):
             if status in (KVPoll.Success, KVPoll.Failed):
                 self.conclude_state = status
             elif status == KVPoll.Bootstrapping:
-                now = time.time()
-                elapsed = now - self.init_time
-                if elapsed >= self.kv_mgr.bootstrap_time_out:
-                    self.kv_mgr.record_failure(
-                        self.bootstrap_room,
-                        f"Request {self.bootstrap_room} timed out after {elapsed:.1f}s in KVPoll.Bootstrapping",
-                    )
-                    self.conclude_state = KVPoll.Failed
-                    return KVPoll.Failed
+                if self.init_time is not None:
+                    now = time.time()
+                    elapsed = now - self.init_time
+                    if elapsed >= self.kv_mgr.bootstrap_time_out:
+                        self.kv_mgr.record_failure(
+                            self.bootstrap_room,
+                            f"Request {self.bootstrap_room} timed out after {elapsed:.1f}s in KVPoll.Bootstrapping",
+                        )
+                        self.conclude_state = KVPoll.Failed
+                        return KVPoll.Failed
 
             return status
         else: