[Core] Add `reload_weights` RPC method (#20096)

Signed-off-by: 22quinn <33176974+22quinn@users.noreply.github.com>

tests/v1/worker/test_gpu_model_runner.py

@@ -460,11 +460,16 @@ def test_load_model_weights_inplace(dist_init, model_runner, model_runner_2):
         {"load_config": {
             "load_format": original_load_format
         }})
-    model_runner_2.load_model()  # Load real weights inplace
+    model_runner_2.reload_weights()  # Load real weights inplace
     assert str(model_runner.get_model().state_dict()) == str(
         model_runner_2.get_model().state_dict())
 
 
+def test_reload_weights_before_load_model(model_runner):
+    with pytest.raises(AssertionError):
+        model_runner.reload_weights()
+
+
 def test_init_kv_cache_with_kv_sharing_invalid_target_layer_order():
     torch.set_default_dtype(torch.float16)
     layer_0 = "model.layers.0.self_attn.attn"

vllm/v1/worker/gpu_model_runner.py

@@ -1873,17 +1873,9 @@ class GPUModelRunner(LoRAModelRunnerMixin):
         with DeviceMemoryProfiler() as m:
             time_before_load = time.perf_counter()
             model_loader = get_model_loader(self.load_config)
-            if not hasattr(self, "model"):
             logger.info("Loading model from scratch...")
             self.model = model_loader.load_model(
-                    vllm_config=self.vllm_config,
-                    model_config=self.model_config)
-            else:
-                logger.info(
-                    "Model was already initialized. Loading weights inplace..."
-                )
-                model_loader.load_weights(self.model,
-                                          model_config=self.model_config)
+                vllm_config=self.vllm_config, model_config=self.model_config)
             if self.lora_config:
                 self.model = self.load_lora_model(self.model,
                                                   self.model_config,
@@ -1916,6 +1908,13 @@ class GPUModelRunner(LoRAModelRunnerMixin):
                 rank_mapping,
             )
 
+    def reload_weights(self) -> None:
+        assert getattr(self, "model", None) is not None, \
+            "Cannot reload weights before model is loaded."
+        model_loader = get_model_loader(self.load_config)
+        logger.info("Reloading weights inplace...")
+        model_loader.load_weights(self.model, model_config=self.model_config)
+
     def save_tensorized_model(
         self,
         tensorizer_config: "TensorizerConfig",

vllm/v1/worker/gpu_worker.py

@@ -4,6 +4,7 @@
 import copy
 import gc
 import os
+from contextlib import AbstractContextManager, nullcontext
 from typing import TYPE_CHECKING, Any, Optional
 
 import torch
@@ -118,6 +119,21 @@ class Worker(WorkerBase):
                     buffer.data.copy_(self._sleep_saved_buffers[name].data)
             self._sleep_saved_buffers = {}
 
+    def _maybe_get_memory_pool_context(self,
+                                       tag: str) -> AbstractContextManager:
+        if self.vllm_config.model_config.enable_sleep_mode:
+            from vllm.device_allocator.cumem import CuMemAllocator
+
+            allocator = CuMemAllocator.get_instance()
+            if tag == "weights":
+                assert allocator.get_current_usage() == 0, (
+                    "Sleep mode can only be "
+                    "used for one instance per process.")
+            context = allocator.use_memory_pool(tag=tag)
+        else:
+            context = nullcontext()
+        return context
+
     def initialize_cache(self, num_gpu_blocks: int,
                          num_cpu_blocks: int) -> None:
         self.cache_config.num_gpu_blocks = num_gpu_blocks
@@ -179,24 +195,17 @@ class Worker(WorkerBase):
     # FIXME(youkaichao & ywang96): Use TorchDispatchMode instead of memory pool
     # to hijack tensor allocation.
     def load_model(self) -> None:
-        if self.vllm_config.model_config.enable_sleep_mode:
-            from vllm.device_allocator.cumem import CuMemAllocator
-
-            allocator = CuMemAllocator.get_instance()
-            assert allocator.get_current_usage() == 0, (
-                "Sleep mode can only be "
-                "used for one instance per process.")
-            context = allocator.use_memory_pool(tag="weights")
-        else:
-            from contextlib import nullcontext
-            context = nullcontext()
         eep_scale_up = os.environ.get("VLLM_ELASTIC_EP_SCALE_UP_LAUNCH") == "1"
-        with context:
+        with self._maybe_get_memory_pool_context(tag="weights"):
             self.model_runner.load_model(eep_scale_up=eep_scale_up)
 
     def update_config(self, overrides: dict[str, Any]) -> None:
         self.model_runner.update_config(overrides)
 
+    def reload_weights(self) -> None:
+        with self._maybe_get_memory_pool_context(tag="weights"):
+            self.model_runner.reload_weights()
+
     @torch.inference_mode()
     def determine_available_memory(self) -> int:
         """Profiles the peak memory usage of the model to determine how much 

vllm/v1/worker/tpu_model_runner.py

@@ -1174,16 +1174,10 @@ class TPUModelRunner(LoRAModelRunnerMixin):
                         mesh=self.mesh)
                 else:
                     model_loader = get_model_loader(self.load_config)
-                    if not hasattr(self, "model"):
                     logger.info("Loading model from scratch...")
                     model = model_loader.load_model(
                         vllm_config=self.vllm_config,
                         model_config=self.model_config)
-                    else:
-                        logger.info("Model was already initialized. \
-                                Loading weights inplace...")
-                        model_loader.load_weights(
-                            self.model, model_config=self.model_config)
             except RuntimeError as e:
                 raise RuntimeError(
                     f"Unable to load model, a likely reason is the model is "
@@ -1205,6 +1199,13 @@ class TPUModelRunner(LoRAModelRunnerMixin):
             self.model = model
         self.sampler = TPUSampler()
 
+    def reload_weights(self) -> None:
+        assert getattr(self, "model", None) is not None, \
+            "Cannot reload weights before model is loaded."
+        model_loader = get_model_loader(self.load_config)
+        logger.info("Reloading weights inplace...")
+        model_loader.load_weights(self.model, model_config=self.model_config)
+
     @torch.no_grad()
     def _dummy_run(self, num_tokens: int, num_reqs: int,
                    num_blocks: int) -> None:

vllm/v1/worker/tpu_worker.py

@@ -265,6 +265,9 @@ class TPUWorker:
     def update_config(self, overrides: dict[str, Any]) -> None:
         self.model_runner.update_config(overrides)
 
+    def reload_weights(self) -> None:
+        self.model_runner.reload_weights()
+
     def compile_or_warm_up_model(self) -> None:
         if not self.model_config.enforce_eager:
             self.model_runner.capture_model()