[Bugfix] Allow ScalarType to be compiled with pytorch 2.3 and add checks for registering FakeScalarType and dynamo support. (#7886)

csrc/core/scalar_type.hpp

@@ -387,7 +387,8 @@ class ScalarTypeTorch : public torch::CustomClassHolder, public ScalarType {
   // This needs to be implemented and throw a TypeError in order for
   // PyTorch's opcheck to work on ops that use ScalarTypes.
   int64_t len() const {
-    throw c10::TypeError("__len__ not implemented");
+    throw c10::TypeError({__func__, __FILE__, static_cast<uint32_t>(__LINE__)},
+                         "__len__ not implemented");
     return 0;
   }
 

vllm/_core_ext.py

@@ -181,6 +181,8 @@ elif core_C_available:
 
     ScalarType = torch.classes._core_C.ScalarType
 
+    if (hasattr(torch, "_library")
+            and hasattr(torch._library, "register_fake_class")):
         # Needed for dynamo support of ScalarType.
         @torch._library.register_fake_class("_core_C::ScalarType")
         class FakeScalarType:
@@ -249,9 +251,11 @@ elif core_C_available:
 
             @classmethod
             def __obj_unflatten__(
-                cls, flat_type: Tuple[Tuple[str, Any], ...]) -> 'ScalarType':
+                    cls, flat_type: Tuple[Tuple[str, Any],
+                                          ...]) -> 'ScalarType':
                 return cls(
-                torch.classes._core_C.ScalarType.__obj_unflatten__(flat_type))
+                    torch.classes._core_C.ScalarType.__obj_unflatten__(
+                        flat_type))
 
             @classmethod
             def int_(cls, size_bits: int, bias: Optional[int]) -> 'ScalarType':
@@ -262,11 +266,13 @@ elif core_C_available:
                 return ScalarType.uint(size_bits, bias)
 
             @classmethod
-        def float_IEEE754(cls, exponent: int, mantissa: int) -> 'ScalarType':
+            def float_IEEE754(cls, exponent: int,
+                              mantissa: int) -> 'ScalarType':
                 return ScalarType.float_IEEE754(exponent, mantissa)
 
             @classmethod
-        def float_(cls, exponent: int, mantissa: int, finite_values_only: bool,
+            def float_(cls, exponent: int, mantissa: int,
+                       finite_values_only: bool,
                        nan_repr: int) -> 'ScalarType':
-            return ScalarType.float_(exponent, mantissa, finite_values_only,
-                                     nan_repr)
+                return ScalarType.float_(exponent, mantissa,
+                                         finite_values_only, nan_repr)

vllm/utils.py

@@ -25,6 +25,7 @@ import numpy.typing as npt
 import psutil
 import torch
 import torch.types
+from packaging.version import Version
 from typing_extensions import ParamSpec, TypeIs, assert_never
 
 import vllm.envs as envs
@@ -1114,3 +1115,11 @@ async def _run_task_with_lock(task: Callable, lock: asyncio.Lock, *args,
     """Utility function to run async task in a lock"""
     async with lock:
         return await task(*args, **kwargs)
+
+
+# Using dynamo with vLLM doesn't really work well with PyTorch versions < 2.4.0.
+# In particular, the FakeScalarType is not supported for earlier versions of
+# PyTorch which breaks dynamo for any ops registered using ScalarType.
+def supports_dynamo() -> bool:
+    base_torch_version = Version(Version(torch.__version__).base_version)
+    return base_torch_version >= Version("2.4.0")

vllm/worker/model_runner.py

@@ -44,7 +44,8 @@ from vllm.sampling_params import SamplingParams
 from vllm.sequence import (IntermediateTensors, SamplerOutput,
                            SequenceGroupMetadata)
 from vllm.utils import (CudaMemoryProfiler, PyObjectCache, async_tensor_h2d,
-                        flatten_2d_lists, is_hip, is_pin_memory_available)
+                        flatten_2d_lists, is_hip, is_pin_memory_available,
+                        supports_dynamo)
 from vllm.worker.model_runner_base import (
     ModelRunnerBase, ModelRunnerInputBase, ModelRunnerInputBuilderBase,
     _add_attn_metadata_broadcastable_dict,
@@ -946,7 +947,7 @@ class GPUModelRunnerBase(ModelRunnerBase[TModelInputForGPU]):
                     "provided. Defaulting to scaling factors of 1.0. "
                     "This may lead to less accurate results!")
 
-        if envs.VLLM_TEST_DYNAMO_GRAPH_CAPTURE:
+        if envs.VLLM_TEST_DYNAMO_GRAPH_CAPTURE and supports_dynamo():
             self.model = torch.compile(self.model,
                                        fullgraph=True,
                                        backend="eager")