diff --git a/benchmark/benchmark_serving.py b/benchmark/benchmark_serving.py
index b5afe3b7..c915e1f5 100644
--- a/benchmark/benchmark_serving.py
+++ b/benchmark/benchmark_serving.py
@@ -424,7 +424,7 @@ async def benchmark(
     allow_variable_generation_length: bool,
     verbose: bool,
     results_filename: str,
-    ip_ports: list[int],
+    ip_ports: List[int],
     distribution: str,
     qps: float,
     coefficient_variation: float,
diff --git a/llumnix/backends/vllm/executor.py b/llumnix/backends/vllm/executor.py
index 8cfd136f..c3fd183a 100644
--- a/llumnix/backends/vllm/executor.py
+++ b/llumnix/backends/vllm/executor.py
@@ -36,6 +36,7 @@
 class LlumnixRayGPUExecutor(RayGPUExecutor):
     def _init_workers_ray(self, placement_group: "PlacementGroup",
                           **ray_remote_kwargs):
+        self.last_inference_latency = 0
         if self.parallel_config.tensor_parallel_size == 1:
             # For single GPU case, we use a ray worker with constrained memory.
             num_gpus = self.cache_config.gpu_memory_utilization
@@ -73,7 +74,7 @@ def _init_workers_ray(self, placement_group: "PlacementGroup",
                 num_cpus=0,
                 num_gpus=num_gpus,
                 scheduling_strategy=scheduling_strategy,
-                max_concurrency=4,
+                max_concurrency=2,
                 **ray_remote_kwargs,
             )(RayWorkerWrapper).remote(
                 worker_module_name="llumnix.backends.vllm.worker",
@@ -146,10 +147,18 @@ def _init_workers_ray(self, placement_group: "PlacementGroup",
                           max_concurrent_workers=self.parallel_config.
                           max_parallel_loading_workers)
 
+    def execute_model(self, *args, **kwargs):
+        t0 = time.time()
+        outputs = super().execute_model(*args, **kwargs)
+        t1 = time.time()
+        self.last_inference_latency = (t1 - t0) * 1000
+        return outputs
+
 class SimGPUExecutor(GPUExecutor):
     latency_mem: LatencyMemData = None
     def __init__(self, *args, **kwargs) -> None:
         super().__init__(*args, **kwargs)
+        self.last_inference_latency = 0
         self.migration_bandwidth = self.latency_mem.migration_bandwidth
         # TODO(ziming) add swap bandwidth
 
@@ -187,10 +196,13 @@ def execute_model(
         decode_bs = _pad_to_alignment(decode_bs, 8)
         latency = 0
         if prefill_seq_len:
-            latency += model_prefill(prefill_seq_len, *self.latency_mem.prefill_model_params) / 1000
+            latency += self.latency_mem.prefill_latency[prefill_seq_len][0] if prefill_seq_len in self.latency_mem.prefill_latency \
+                       else model_prefill(prefill_seq_len, *self.latency_mem.prefill_model_params)
         if decode_bs:
-            latency += model_decode((decode_bs, decode_seq_len), *self.latency_mem.decode_model_params) / 1000
-        time.sleep(latency)
+            decode_meta_data = (decode_bs, decode_seq_len)
+            latency += self.latency_mem.decode_latency[decode_meta_data][0] if decode_meta_data in self.latency_mem.decode_latency \
+                       else model_decode((decode_bs, decode_seq_len), *self.latency_mem.decode_model_params)
+        time.sleep(latency/1000)
         sampler_outputs = []
         for meta_data in execute_model_req.seq_group_metadata_list:
             samples = []
diff --git a/llumnix/backends/vllm/llm_engine.py b/llumnix/backends/vllm/llm_engine.py
index c3311d1a..cee6cd1a 100644
--- a/llumnix/backends/vllm/llm_engine.py
+++ b/llumnix/backends/vllm/llm_engine.py
@@ -177,9 +177,7 @@ def send_blocks(self, dst_ray_actor: "ray.actor.ActorHandle", src_blocks: List[i
                                                            src_worker_handle_list=self.worker_handle_list))
 
     def step(self) -> Tuple[List[RequestOutput], InstanceInfo, List[ServerInfo]]:
-        t0_inference_begin = time.time()
         output_list = self.engine.step()
-        t1_inference_end = time.time()
 
         instance_info: InstanceInfo = self.engine.scheduler.get_record_instance_info()
 
@@ -191,7 +189,7 @@ def step(self) -> Tuple[List[RequestOutput], InstanceInfo, List[ServerInfo]]:
         instance_info.instance_id = self.instance_id
         instance_info.step_id = next(self.step_counter)
         instance_info.timestamp = time.time()
-        instance_info.latency = (t1_inference_end - t0_inference_begin)*1000
+        instance_info.latency = self.engine.model_executor.last_inference_latency
         seq_groups = self.engine.scheduler.running
         if seq_groups:
             tot_blocks = []
diff --git a/llumnix/entrypoints/vllm/api_server.py b/llumnix/entrypoints/vllm/api_server.py
index 21663cd9..344b879b 100644
--- a/llumnix/entrypoints/vllm/api_server.py
+++ b/llumnix/entrypoints/vllm/api_server.py
@@ -49,7 +49,8 @@
 
 async def _background_process_outputs():
     while True:
-        request_outputs = request_output_queue.get_nowait_batch(num_items=request_output_queue.qsize())
+        qsize = await request_output_queue.actor.qsize.remote()
+        request_outputs = await request_output_queue.actor.get_nowait_batch.remote(qsize)
         for request_output in request_outputs:
             request_id = request_output.request_id
             # Request could be dispatched twice when manager is dead, the first request will free the request_streams when finished.
@@ -59,7 +60,6 @@ async def _background_process_outputs():
             if request_output.finished:
                 request_streams[request_id].finish()
                 del request_streams[request_id]
-        await asyncio.sleep(0.01)
 
 # pylint: disable=unused-argument
 @asynccontextmanager