[Doc][0.18.0][KV Pool]add mooncake rdma timeout (#7784)

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### What this PR does / why we need it?
- Add `default_kv_lease_ttl` to the `mooncake.json` example in the KV
Pool guide.
- Document `default_kv_lease_ttl` semantics and clarify that it should
be larger than `ASCEND_CONNECT_TIMEOUT` and `ASCEND_TRANSFER_TIMEOUT`.
- Add `HCCL_RDMA_TIMEOUT` explanation for Mooncake RDMA retransmission
timeout, including the recommended constraint note.
- Add `HCCL_RDMA_TIMEOUT=16` to relevant KV Pool environment setup
examples for consistency.

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---------

Signed-off-by: Pz1116 <zpbzpb123123@gmail.com>

docs/source/user_guide/feature_guide/kv_pool.md

@@ -99,6 +99,11 @@ export PYTHONHASHSEED=0
 | 800 I/T A3 series | 25.5.0<=HDK<26.0.0 | `export ASCEND_BUFFER_POOL=4:8` | Configures the number and size of buffers on the NPU Device for aggregation and KV transfer (e.g., `4:8` means 4 buffers of 8MB). |
 | 800 I/T A2 series | N/A | `export HCCL_INTRA_ROCE_ENABLE=1` | Required by direct transmission cheme on 800 I/T A2 series|
 
+### FAQ for HIXL (ascend_direct) backend
+
+For common troubleshooting and issue localization guidance for HIXL (ascend_direct), see:
+<https://gitcode.com/cann/hixl/wiki/HIXL%E5%B8%B8%E8%A7%81%E9%97%AE%E9%A2%98%E5%AE%9A%E4%BD%8D%E6%89%8B%E5%86%8C.md>
+
 ### Run Mooncake Master
 
 #### 1.Configure mooncake.json
@@ -126,10 +131,11 @@ The environment variable **MOONCAKE_CONFIG_PATH** is configured to the full path
 Under the mooncake folder:
 
 ```shell
-mooncake_master --port 50088 --eviction_high_watermark_ratio 0.9 --eviction_ratio 0.1
+mooncake_master --port 50088 --eviction_high_watermark_ratio 0.9 --eviction_ratio 0.1 --default_kv_lease_ttl 11000
 ```
 
 `eviction_high_watermark_ratio` determines the watermark where Mooncake Store will perform eviction，and `eviction_ratio` determines the portion of stored objects that would be evicted.
+`default_kv_lease_ttl` controls the default lease TTL for KV objects (milliseconds); configure it via `--default_kv_lease_ttl` and keep it larger than `ASCEND_CONNECT_TIMEOUT` and `ASCEND_TRANSFER_TIMEOUT`.
 
 ### PD Disaggregation Scenario
 
@@ -157,6 +163,11 @@ export ASCEND_ENABLE_USE_FABRIC_MEM=1
 #A2
 #export HCCL_INTRA_ROCE_ENABLE=1
 
+#Minimum retransmission timeout of the RDMA，equals 4.096 μs * 2 ^ timeout.
+#Needs to satisfy the equation: ASCEND_TRANSFER_TIMEOUT > RDMA_TIMEOUT * 7, where 7 is the default number of retry for RDMA transfer.
+#HCCL_RDMA_TIMEOUT also affects collective communication behavior and should be configured carefully.
+export HCCL_RDMA_TIMEOUT=17
+
 # Unit: ms. The timeout for one-sided communication connection establishment is set to 10 seconds by default (see PR: https://github.com/kvcache-ai/Mooncake/pull/1039). Users can adjust this value based on their specific setup.
 # The recommended formula is: ASCEND_CONNECT_TIMEOUT = connection_time_per_card (typically within 500ms) × total_number_of_Decode_cards.
 # This ensures that even in the worst-case scenario—where all Decode cards simultaneously attempt to connect to the same Prefill card the connection will not time out.
@@ -229,6 +240,7 @@ export ACL_OP_INIT_MODE=1
 export ASCEND_ENABLE_USE_FABRIC_MEM=1
 #A2
 #export HCCL_INTRA_ROCE_ENABLE=1
+export HCCL_RDMA_TIMEOUT=17
 export ASCEND_CONNECT_TIMEOUT=10000
 export ASCEND_TRANSFER_TIMEOUT=10000
 
@@ -343,6 +355,7 @@ export ACL_OP_INIT_MODE=1
 export ASCEND_ENABLE_USE_FABRIC_MEM=1
 #A2
 #export HCCL_INTRA_ROCE_ENABLE=1
+export HCCL_RDMA_TIMEOUT=17
 export ASCEND_CONNECT_TIMEOUT=10000
 export ASCEND_TRANSFER_TIMEOUT=10000