Adjust max prefix len (#980)

python/sglang/srt/managers/schedule_batch.py

@@ -163,11 +163,21 @@ class Req:
         return self.finished_reason is not None
 
     def adjust_max_prefix_ids(self):
-        max_prefix_ids = self.input_ids
+        input_len = len(self.input_ids)
+        max_prefix_len = input_len
+
+        if self.sampling_params.max_new_tokens > 0:
+            # Need at least one token to compute logits
+            max_prefix_len = min(max_prefix_len, input_len - 1)
+
         if self.return_logprob:
-            max_prefix_ids = self.input_ids[: self.logprob_start_len]
+            max_prefix_len = min(max_prefix_len, self.logprob_start_len)
+
+            if self.normalized_prompt_logprob is None:
+                # Need at least two tokens to compute normalized logprob
+                max_prefix_len = min(max_prefix_len, input_len - 2)
 
-        return max_prefix_ids
+        return self.input_ids[:max_prefix_len]
 
     # Based on https://github.com/vllm-project/vllm/blob/7a64d24aad69e4d2548aa0bf528d9fe63428ab01/vllm/transformers_utils/detokenizer.py#L194-L313
     def init_incremental_detokenize(self):

python/sglang/srt/managers/tp_worker.py

@@ -387,23 +387,6 @@ class ModelTpServer:
 
         for req in self.waiting_queue:
 
-            # FIXME: Move this code into adjust_max_prefix_len
-            if req.return_logprob and req.normalized_prompt_logprob is None:
-                # Need at least two tokens to compute normalized logprob
-                if req.extend_input_len < 2:
-                    delta = 2 - req.extend_input_len
-                    req.extend_input_len += delta
-                    req.prefix_indices = req.prefix_indices[:-delta]
-                    if req.image_offset is not None:
-                        req.image_offset += delta
-
-            if req.extend_input_len == 0 and req.sampling_params.max_new_tokens > 0:
-                # Need at least one token to compute logits
-                req.extend_input_len = 1
-                req.prefix_indices = req.prefix_indices[:-1]
-                if req.image_offset is not None:
-                    req.image_offset += 1
-
             res = adder.add_one_req(req)
             if (
                 not res