[Core] Enable command line logging for LLMEngine (#25610)

Co-authored-by: Ye (Charlotte) Qi <yeq@meta.com>
Signed-off-by: Zhuohan Li <zhuohan123@gmail.com>

vllm/v1/engine/llm_engine.py

 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
+import time
 from collections.abc import Mapping
 from copy import copy
 from typing import Any, Callable, Optional, Union
@@ -31,8 +32,7 @@ from vllm.v1.engine.output_processor import OutputProcessor
 from vllm.v1.engine.parallel_sampling import ParentRequest
 from vllm.v1.engine.processor import Processor
 from vllm.v1.executor.abstract import Executor
-from vllm.v1.metrics.loggers import (PrometheusStatLogger, StatLoggerBase,
-                                     StatLoggerFactory)
+from vllm.v1.metrics.loggers import StatLoggerFactory, StatLoggerManager
 from vllm.v1.metrics.reader import Metric, get_metrics_snapshot
 from vllm.v1.metrics.stats import IterationStats
 from vllm.v1.worker.worker_base import WorkerBase
@@ -74,9 +74,6 @@ class LLMEngine:
         self.cache_config = vllm_config.cache_config
 
         self.log_stats = log_stats
-        self.stat_logger: Optional[StatLoggerBase] = None
-        if self.log_stats:
-            self.stat_logger = PrometheusStatLogger(vllm_config)
 
         executor_backend = (
             self.vllm_config.parallel_config.distributed_executor_backend)
@@ -122,6 +119,15 @@ class LLMEngine:
             log_stats=self.log_stats,
         )
 
+        self.logger_manager: Optional[StatLoggerManager] = None
+        if self.log_stats:
+            self.logger_manager = StatLoggerManager(
+                vllm_config=vllm_config,
+                custom_stat_loggers=stat_loggers,
+                enable_default_loggers=log_stats,
+            )
+            self.logger_manager.log_engine_initialized()
+
         if not multiprocess_mode:
             # for v0 compatibility
             self.model_executor = self.engine_core.engine_core.model_executor  # type: ignore
@@ -269,10 +275,13 @@ class LLMEngine:
         self.engine_core.abort_requests(processed_outputs.reqs_to_abort)
 
         # 4) Record stats
-        if self.stat_logger is not None:
+        if self.logger_manager is not None:
             assert outputs.scheduler_stats is not None
-            self.stat_logger.record(scheduler_stats=outputs.scheduler_stats,
-                                    iteration_stats=iteration_stats)
+            self.logger_manager.record(
+                scheduler_stats=outputs.scheduler_stats,
+                iteration_stats=iteration_stats,
+            )
+            self.do_log_stats_with_interval()
 
         return processed_outputs.request_outputs
 
@@ -315,6 +324,20 @@ class LLMEngine:
 
         return self.tokenizer
 
+    def do_log_stats(self) -> None:
+        """Log stats if logging is enabled."""
+        if self.logger_manager:
+            self.logger_manager.log()
+
+    def do_log_stats_with_interval(self) -> None:
+        """Log stats when the time interval has passed."""
+        now = time.time()
+        if not hasattr(self, "_last_log_time"):
+            self._last_log_time = now
+        if now - self._last_log_time >= envs.VLLM_LOG_STATS_INTERVAL:
+            self.do_log_stats()
+            self._last_log_time = now
+
     def add_lora(self, lora_request: LoRARequest) -> bool:
         """Load a new LoRA adapter into the engine for future requests."""
         return self.engine_core.add_lora(lora_request)

vllm/v1/metrics/loggers.py

@@ -90,7 +90,6 @@ class LoggingStatLogger(StatLoggerBase):
                iteration_stats: Optional[IterationStats],
                engine_idx: int = 0):
         """Log Stats to standard output."""
-
         if iteration_stats:
             self._track_iteration_stats(iteration_stats)