[Bugfix][Core] Fix negative prompt token counter increments with external KV cache accounting

tests/v1/metrics/test_stats.py

@@ -116,7 +116,7 @@ def test_prompt_token_stats_all_computed():
     # Case 1: No caching (All tokens computed locally)
     stats.update_from_output(
         num_cached_tokens=0,
-        num_external_computed_tokens=0,
+        num_external_cached_tokens=0,
         prompt_len=1000,
     )
 
@@ -133,7 +133,7 @@ def test_prompt_token_stats_partial_local_cache():
     # Case 2: Partial local cache
     stats.update_from_output(
         num_cached_tokens=300,
-        num_external_computed_tokens=0,
+        num_external_cached_tokens=0,
         prompt_len=1000,
     )
 
@@ -149,7 +149,7 @@ def test_prompt_token_stats_partial_external_transfer():
     # Case 3: Partial external transfer
     stats.update_from_output(
         num_cached_tokens=500,
-        num_external_computed_tokens=500,
+        num_external_cached_tokens=500,
         prompt_len=1000,
     )
 
@@ -165,7 +165,7 @@ def test_prompt_token_stats_mixed_sources():
     # Case 4: Mixed sources
     stats.update_from_output(
         num_cached_tokens=600,
-        num_external_computed_tokens=200,
+        num_external_cached_tokens=200,
         prompt_len=1000,
     )
 
@@ -185,7 +185,7 @@ def test_prompt_token_stats_full_local_cache_recompute():
     # Case 5: Full local cache (999 cached after reduction, 1 recomputed)
     stats.update_from_output(
         num_cached_tokens=999,
-        num_external_computed_tokens=0,
+        num_external_cached_tokens=0,
         prompt_len=1000,
     )
 
@@ -201,7 +201,7 @@ def test_prompt_token_stats_full_external_transfer_recompute():
     # Case 6: Full external transfer (999 cached after reduction, 1 recomputed)
     stats.update_from_output(
         num_cached_tokens=999,
-        num_external_computed_tokens=1000,
+        num_external_cached_tokens=1000,
         prompt_len=1000,
     )
 

vllm/v1/core/sched/scheduler.py

@@ -829,6 +829,9 @@ def schedule(self) -> SchedulerOutput:
                 # Count the number of prefix cached tokens.
                 if request.num_cached_tokens < 0:
                     request.num_cached_tokens = num_computed_tokens
+                    request.num_external_cached_tokens = (
+                        request.num_external_computed_tokens
+                    )
                 # Encoder-related.
                 if encoder_inputs_to_schedule:
                     scheduled_encoder_inputs[request_id] = encoder_inputs_to_schedule
@@ -1468,7 +1471,7 @@ def update_from_output(
                         kv_transfer_params=kv_transfer_params,
                         trace_headers=request.trace_headers,
                         num_cached_tokens=request.num_cached_tokens,
-                        num_external_computed_tokens=request.num_external_computed_tokens,
+                        num_external_cached_tokens=request.num_external_cached_tokens,
                         routed_experts=routed_experts,
                         num_nans_in_logits=request.num_nans_in_logits,
                     )
@@ -2072,6 +2075,7 @@ def _update_waiting_for_remote_kv(self, request: Request) -> None:
             # Count the number of prefix cached tokens.
             if request.num_cached_tokens < 0:
                 request.num_cached_tokens = request.num_computed_tokens
+                request.num_external_cached_tokens = request.num_external_computed_tokens
 
         self.finished_recving_kv_req_ids.remove(request.request_id)
 

vllm/v1/request.py

@@ -162,6 +162,9 @@ def __init__(
         # The number of tokens that have been computed remotely.
         self.num_external_computed_tokens = 0
 
+        # The number of tokens fetched from an external KV cache.
+        self.num_external_cached_tokens = -1
+
         self.block_hashes: list[BlockHash] = []
         # Store the block hasher without binding self to avoid creating a
         # reference cycle (Request -> partial -> Request) that prevents