diff --git a/python/sglang/srt/managers/schedule_batch.py b/python/sglang/srt/managers/schedule_batch.py
index 9263b9c3b..373ffbcc3 100644
--- a/python/sglang/srt/managers/schedule_batch.py
+++ b/python/sglang/srt/managers/schedule_batch.py
@@ -1114,10 +1114,17 @@ class Req:
         self.has_log_time_stats = True
 
     def set_extend_input_len(self, extend_input_len: int):
+        # Setting extend_input_len and computing the relative logprob_start_len in an extend batch
+        #
+        # Key variables:
+        # - logprob_start_len: Absolute position in full sequence where logprob computation begins
+        # - extend_logprob_start_len: Relative position within current extend batch where logprob computation begins
+        # - extend_input_len: Number of tokens that need to be processed in this extend batch
         self.extend_input_len = extend_input_len
         if self.logprob_start_len == -1:
             logprob_start_len = len(self.fill_ids) - 1
         else:
+            # logprob_start_len should be at least the length of the prefix indices
             logprob_start_len = max(self.logprob_start_len, len(self.prefix_indices))
         self.extend_logprob_start_len = min(
             logprob_start_len - len(self.prefix_indices),