[V1][Metrics] Add TTFT and TPOT histograms (#12530)

Signed-off-by: Mark McLoughlin <markmc@redhat.com>

tests/entrypoints/openai/test_metrics.py

@@ -208,6 +208,12 @@ EXPECTED_METRICS_V1 = [
     "vllm:request_generation_tokens_sum",
     "vllm:request_generation_tokens_bucket",
     "vllm:request_generation_tokens_count",
+    "vllm:time_to_first_token_seconds_sum",
+    "vllm:time_to_first_token_seconds_bucket",
+    "vllm:time_to_first_token_seconds_count",
+    "vllm:time_per_output_token_seconds_sum",
+    "vllm:time_per_output_token_seconds_bucket",
+    "vllm:time_per_output_token_seconds_count",
 ]
 
 

vllm/v1/engine/output_processor.py

@@ -27,6 +27,7 @@ class RequestState:
         prompt: Optional[str],
         prompt_token_ids: List[int],
         detokenizer: IncrementalDetokenizer,
+        arrival_time: float,
         queue: Optional[asyncio.Queue[RequestOutput]],
     ):
         self.request_id = request_id
@@ -37,7 +38,7 @@ class RequestState:
         self.is_prefilling = True
         self.queue = queue
 
-        self.stats = RequestStateStats()
+        self.stats = RequestStateStats(last_token_time=arrival_time)
 
     @classmethod
     def from_new_request(
@@ -54,6 +55,7 @@ class RequestState:
                 tokenizer=tokenizer,
                 request=request,
             ),
+            arrival_time=request.arrival_time,
             queue=queue,
         )
 

vllm/v1/metrics/loggers.py

@@ -121,6 +121,26 @@ class PrometheusStatLogger(StatLoggerBase):
                 buckets=build_1_2_5_buckets(max_model_len),
                 labelnames=labelnames).labels(*labelvalues)
 
+        self.histogram_time_to_first_token = \
+            prometheus_client.Histogram(
+                name="vllm:time_to_first_token_seconds",
+                documentation="Histogram of time to first token in seconds.",
+                buckets=[
+                    0.001, 0.005, 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, 0.25, 0.5,
+                    0.75, 1.0, 2.5, 5.0, 7.5, 10.0
+                ],
+                labelnames=labelnames).labels(*labelvalues)
+
+        self.histogram_time_per_output_token = \
+            prometheus_client.Histogram(
+                name="vllm:time_per_output_token_seconds",
+                documentation="Histogram of time per output token in seconds.",
+                buckets=[
+                    0.01, 0.025, 0.05, 0.075, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5,
+                    0.75, 1.0, 2.5
+                ],
+                labelnames=labelnames).labels(*labelvalues)
+
     def log(self, scheduler_stats: SchedulerStats,
             iteration_stats: IterationStats):
         """Log to prometheus."""
@@ -137,6 +157,11 @@ class PrometheusStatLogger(StatLoggerBase):
             self.histogram_num_generation_tokens_request.observe(
                 finished_request.num_generation_tokens)
 
+        for ttft in iteration_stats.time_to_first_tokens_iter:
+            self.histogram_time_to_first_token.observe(ttft)
+        for tpot in iteration_stats.time_per_output_tokens_iter:
+            self.histogram_time_per_output_token.observe(tpot)
+
     @staticmethod
     def _unregister_vllm_metrics():
         # Unregister any existing vLLM collectors (for CI/CD

vllm/v1/metrics/stats.py

+import time
 from dataclasses import dataclass
 from typing import TYPE_CHECKING, List
 
@@ -22,6 +23,7 @@ class RequestStateStats:
     """Stats that need to be tracked across delta updates."""
 
     num_generation_tokens: int = 0
+    last_token_time: float = 0.0
 
 
 @dataclass
@@ -40,6 +42,8 @@ class IterationStats:
         self.num_generation_tokens = 0
         self.num_prompt_tokens = 0
         self.finished_requests: List[FinishedRequestStats] = []
+        self.time_to_first_tokens_iter: List[float] = []
+        self.time_per_output_tokens_iter: List[float] = []
 
     def update_from_output(self, output: "EngineCoreOutput",
                            is_prefilling: bool, prompt_len: int,
@@ -48,6 +52,8 @@ class IterationStats:
             return
 
         num_new_generation_tokens = len(output.new_token_ids)
+        now = time.time()
+        last_token_latency = now - request_state_stats.last_token_time
 
         self.num_generation_tokens += num_new_generation_tokens
         if is_prefilling:
@@ -58,7 +64,12 @@ class IterationStats:
             assert (num_new_generation_tokens > 0)
             self.num_prompt_tokens += prompt_len
 
+            self.time_to_first_tokens_iter.append(last_token_latency)
+        else:
+            self.time_per_output_tokens_iter.append(last_token_latency)
+
         request_state_stats.num_generation_tokens += num_new_generation_tokens
+        request_state_stats.last_token_time = now
 
     def update_from_finished_request(self, request_output: "RequestOutput",
                                      request_state_stats: RequestStateStats):