update hyperparameter guide (#1114)

docs/en/hyperparameter_tuning.md

@@ -10,7 +10,8 @@ When the server is running at full load, look for the following in the log:
 
 ### Tune Your Request Submission Speed
 `#queue-req` indicates the number of requests in the queue. If you frequently see `#queue-req == 0`, it suggests you are bottlenecked by the request submission speed.
-A healthy range for `#queue-req` is `100 - 1000`.
+A healthy range for `#queue-req` is `50 - 1000`.
+On the other hand, do not make `#queue-req` too large because it will also increase the scheduling overhead on the server.
 
 ### Tune `--schedule-conservativeness`
 `token usage` indicates the KV cache memory utilization of the server. `token usage > 0.9` means good utilization.
@@ -19,13 +20,14 @@ The case of serving being too conservative can happen when users send many reque
 
 On the other hand, if you see `token usage` very high and you frequently see warnings like
 `decode out of memory happened, #retracted_reqs: 1, #new_token_ratio: 0.9998 -> 1.0000`, you can increase `--schedule-conservativeness` to a value like 1.3.
+If you see `decode out of memory happened` occasionally but not frequently, it is okay.
 
 ### Tune `--dp-size` and `--tp-size`
 Data parallelism is better for throughput. When there is enough GPU memory, always favor data parallelism for throughput.
 
-### (Minor) Tune `--max-prefill-tokens`, `--mem-fraction-static`, `--max-running-requests`
+### Avoid out-of-memory by tuning `--chunked-prefill-size`, `--mem-fraction-static`, `--max-running-requests`
 If you see out of memory (OOM) errors, you can decrease these parameters.  
-If OOM happens during prefill, try to decrease `--max-prefill-tokens`.  
+If OOM happens during prefill, try to decrease `--chunked-prefill-size` to `4096` or `2048`.  
 If OOM happens during decoding, try to decrease `--max-running-requests`.  
 You can also try to decrease `--mem-fraction-static`, which reduces the memory usage of the KV cache memory pool and helps both prefill and decoding.