chore: logging perf improvments

# What does this PR do?


## Test Plan
# What does this PR do?


## Test Plan

llama_stack/core/routers/inference.py

@@ -63,7 +63,7 @@ from llama_stack.models.llama.llama3.chat_format import ChatFormat
 from llama_stack.models.llama.llama3.tokenizer import Tokenizer
 from llama_stack.providers.datatypes import HealthResponse, HealthStatus, RoutingTable
 from llama_stack.providers.utils.inference.inference_store import InferenceStore
-from llama_stack.providers.utils.telemetry.tracing import get_current_span
+from llama_stack.providers.utils.telemetry.tracing import enqueue_event, get_current_span
 
 logger = get_logger(name=__name__, category="core::routers")
 
@@ -160,7 +160,7 @@ class InferenceRouter(Inference):
         metrics = self._construct_metrics(prompt_tokens, completion_tokens, total_tokens, model)
         if self.telemetry:
             for metric in metrics:
-                await self.telemetry.log_event(metric)
+                enqueue_event(metric)
         return [MetricInResponse(metric=metric.metric, value=metric.value) for metric in metrics]
 
     async def _count_tokens(
@@ -431,7 +431,7 @@ class InferenceRouter(Inference):
                 model=model_obj,
             )
             for metric in metrics:
-                await self.telemetry.log_event(metric)
+                enqueue_event(metric)
 
             # these metrics will show up in the client response.
             response.metrics = (
@@ -537,7 +537,7 @@ class InferenceRouter(Inference):
                 model=model_obj,
             )
             for metric in metrics:
-                await self.telemetry.log_event(metric)
+                enqueue_event(metric)
             # these metrics will show up in the client response.
             response.metrics = (
                 metrics if not hasattr(response, "metrics") or response.metrics is None else response.metrics + metrics
@@ -664,7 +664,7 @@ class InferenceRouter(Inference):
                             "completion_tokens",
                             "total_tokens",
                         ]:  # Only log completion and total tokens
-                            await self.telemetry.log_event(metric)
+                            enqueue_event(metric)
 
                         # Return metrics in response
                         async_metrics = [
@@ -710,7 +710,7 @@ class InferenceRouter(Inference):
             )
             for metric in completion_metrics:
                 if metric.metric in ["completion_tokens", "total_tokens"]:  # Only log completion and total tokens
-                    await self.telemetry.log_event(metric)
+                    enqueue_event(metric)
 
             # Return metrics in response
             return [MetricInResponse(metric=metric.metric, value=metric.value) for metric in completion_metrics]
@@ -806,7 +806,7 @@ class InferenceRouter(Inference):
                             model=model,
                         )
                         for metric in metrics:
-                            await self.telemetry.log_event(metric)
+                            enqueue_event(metric)
 
                 yield chunk
         finally:

llama_stack/providers/utils/telemetry/tracing.py

@@ -18,6 +18,7 @@ from functools import wraps
 from typing import Any
 
 from llama_stack.apis.telemetry import (
+    Event,
     LogSeverity,
     Span,
     SpanEndPayload,
@@ -98,7 +99,7 @@ class BackgroundLogger:
     def __init__(self, api: Telemetry, capacity: int = 100000):
         self.api = api
         self.log_queue: queue.Queue[Any] = queue.Queue(maxsize=capacity)
-        self.worker_thread = threading.Thread(target=self._process_logs, daemon=True)
+        self.worker_thread = threading.Thread(target=self._worker, daemon=True)
         self.worker_thread.start()
         self._last_queue_full_log_time: float = 0.0
         self._dropped_since_last_notice: int = 0
@@ -118,12 +119,16 @@ class BackgroundLogger:
                 self._last_queue_full_log_time = current_time
                 self._dropped_since_last_notice = 0
 
-    def _process_logs(self):
+    def _worker(self):
+        loop = asyncio.new_event_loop()
+        asyncio.set_event_loop(loop)
+        loop.run_until_complete(self._process_logs())
+
+    async def _process_logs(self):
         while True:
             try:
                 event = self.log_queue.get()
-                # figure out how to use a thread's native loop
-                asyncio.run(self.api.log_event(event))
+                await self.api.log_event(event)
             except Exception:
                 import traceback
 
@@ -136,6 +141,19 @@ class BackgroundLogger:
         self.log_queue.join()
 
 
+def enqueue_event(event: Event) -> None:
+    """Enqueue a telemetry event to the background logger if available.
+
+    This provides a non-blocking path for routers and other hot paths to
+    submit telemetry without awaiting the Telemetry API, reducing contention
+    with the main event loop.
+    """
+    global BACKGROUND_LOGGER
+    if BACKGROUND_LOGGER is None:
+        raise RuntimeError("Telemetry API not initialized")
+    BACKGROUND_LOGGER.log_event(event)
+
+
 class TraceContext:
     spans: list[Span] = []
 
@@ -256,11 +274,7 @@ class TelemetryHandler(logging.Handler):
         if record.module in ("asyncio", "selector_events"):
             return
 
-        global CURRENT_TRACE_CONTEXT, BACKGROUND_LOGGER
-
-        if BACKGROUND_LOGGER is None:
-            raise RuntimeError("Telemetry API not initialized")
-
+        global CURRENT_TRACE_CONTEXT
         context = CURRENT_TRACE_CONTEXT.get()
         if context is None:
             return
@@ -269,7 +283,7 @@ class TelemetryHandler(logging.Handler):
         if span is None:
             return
 
-        BACKGROUND_LOGGER.log_event(
+        enqueue_event(
             UnstructuredLogEvent(
                 trace_id=span.trace_id,
                 span_id=span.span_id,