[v1][P/D] Fix a edge case in kv cache schedule (vllm-project#19182)

Co-authored-by: jinghui <jinghui@fb.com>
Signed-off-by: minpeter <kali2005611@gmail.com>

Author: 2 people

vllm/v1/core/sched/scheduler.py

@@ -1009,6 +1009,8 @@ def _update_waiting_for_remote_kv(self, request: Request) -> bool:
         # Now that the blocks are ready, actually cache them.
         block_ids = self.kv_cache_manager.get_block_ids(request.request_id)[0]
         num_computed_tokens = len(block_ids) * self.block_size
+        # Handle the case where num request tokens less then one block.
+        num_computed_tokens = min(num_computed_tokens, request.num_tokens)
         if num_computed_tokens == request.num_tokens:
             num_computed_tokens -= 1
         self.kv_cache_manager.cache_blocks(