[torch.compile][BE] Modify cudagraph callable to check for is_forward_context_set (#36288)

Signed-off-by: Lucas Kabela <lucaskabela@meta.com>

docs/design/torch_compile_multimodal.md

@@ -34,9 +34,6 @@ relies on caching artifacts to reduce start time, we must properly propagate the
 with the LLM text-backbone, or other instances of the same artifact (as is the case with vision block). `is_encoder=True` is also needed for encoder
 components (see Compile Range Integration).
 
-3. `with set_forward_context` context manager should be used around the nn.Module's forward call. This will properly forward the vllm_config which is needed
-for torch.compile integration.
-
 ### CompilationConfig
 
 With the exception of `compile_mm_encoder: true`, the multimodal encoder will inherit from the same compilation config as the text LLM. We may extend

vllm/compilation/cuda_graph.py

@@ -16,7 +16,11 @@ from vllm.compilation.counter import compilation_counter
 from vllm.compilation.monitor import validate_cudagraph_capturing_enabled
 from vllm.config import CUDAGraphMode, VllmConfig
 from vllm.distributed.device_communicators.pynccl_allocator import set_graph_pool_id
-from vllm.forward_context import BatchDescriptor, get_forward_context
+from vllm.forward_context import (
+    BatchDescriptor,
+    get_forward_context,
+    is_forward_context_available,
+)
 from vllm.logger import init_logger
 from vllm.model_executor.offloader.base import get_offloader
 from vllm.platforms import current_platform
@@ -224,6 +228,12 @@ class CUDAGraphWrapper:
         self.concrete_cudagraph_entries.clear()
 
     def __call__(self, *args: Any, **kwargs: Any) -> Any | None:
+        if not is_forward_context_available():
+            # No forward context means we are outside the normal
+            # inference path (e.g. a vision encoder forward pass).
+            # Just run the underlying function without cudagraphs.
+            return self.runnable(*args, **kwargs)
+
         forward_context = get_forward_context()
         batch_descriptor = forward_context.batch_descriptor
         cudagraph_runtime_mode = forward_context.cudagraph_runtime_mode

vllm/model_executor/models/mllama4.py

@@ -38,7 +38,6 @@ from vllm.compilation.decorators import (
 from vllm.config import VllmConfig, set_current_vllm_config
 from vllm.config.multimodal import BaseDummyOptions
 from vllm.distributed import get_tensor_model_parallel_world_size
-from vllm.forward_context import set_forward_context
 from vllm.model_executor.layers.attention import MMEncoderAttention
 from vllm.model_executor.layers.fused_moe import FusedMoE
 from vllm.model_executor.layers.linear import (
@@ -872,9 +871,6 @@ class Llama4ForConditionalGeneration(
         if image_input is None:
             return []
 
-        with (
-            set_forward_context(None, self.vllm_config),
-        ):
         return self._process_image_input(image_input)
 
     def forward(

vllm/model_executor/models/qwen2_5_vl.py

@@ -49,7 +49,6 @@ from vllm.compilation.decorators import (
 from vllm.config import VllmConfig
 from vllm.distributed import parallel_state
 from vllm.distributed import utils as dist_utils
-from vllm.forward_context import set_forward_context
 from vllm.logger import init_logger
 from vllm.model_executor.layers.activation import get_act_and_mul_fn
 from vllm.model_executor.layers.attention import MMEncoderAttention
@@ -1207,7 +1206,6 @@ class Qwen2_5_VLForConditionalGeneration(
             image_embeds = image_input["image_embeds"].type(self.visual.dtype)
         else:
             pixel_values = image_input["pixel_values"]
-            with set_forward_context(None, self.vllm_config):
             if self.use_data_parallel:
                 return run_dp_sharded_mrope_vision_model(
                     self.visual, pixel_values, grid_thw_list, rope_type="rope_3d"
@@ -1262,7 +1260,6 @@ class Qwen2_5_VLForConditionalGeneration(
             video_embeds = video_input["video_embeds"].type(self.visual.dtype)
         else:
             pixel_values_videos = video_input["pixel_values_videos"]
-            with set_forward_context(None, self.vllm_config):
             if self.use_data_parallel:
                 return run_dp_sharded_mrope_vision_model(
                     self.visual,
@@ -1271,9 +1268,7 @@ class Qwen2_5_VLForConditionalGeneration(
                     rope_type="rope_3d",
                 )
             else:
-                    video_embeds = self.visual(
-                        pixel_values_videos, grid_thw=grid_thw_list
-                    )
+                video_embeds = self.visual(pixel_values_videos, grid_thw=grid_thw_list)
 
         # Split concatenated embeddings for each video item.
         merge_size = self.visual.spatial_merge_size