[1/n] Migrate permute_cols to libtorch stable ABI (#31509)

Signed-off-by: Mikayla Gawarecki <mikaylagawarecki@gmail.com>

CMakeLists.txt

@@ -340,7 +340,6 @@ if(VLLM_GPU_LANG STREQUAL "CUDA")
 
   list(APPEND VLLM_EXT_SRC
     "csrc/quantization/awq/gemm_kernels.cu"
-    "csrc/permute_cols.cu"
     "csrc/quantization/w8a8/cutlass/scaled_mm_entry.cu"
     "csrc/quantization/fp4/nvfp4_quant_entry.cu"
     "csrc/quantization/fp4/nvfp4_scaled_mm_entry.cu"
@@ -986,6 +985,48 @@ define_extension_target(
 # Setting this variable sidesteps the issue by calling the driver directly.
 target_compile_definitions(_C PRIVATE CUTLASS_ENABLE_DIRECT_CUDA_DRIVER_CALL=1)
 
+# add OR VLLM_GPU_LANG STREQUAL "HIP" here once
+# https://github.com/vllm-project/vllm/issues/35163 is resolved
+if(VLLM_GPU_LANG STREQUAL "CUDA")
+  #
+  # _C_stable_libtorch extension (ops registered via STABLE_TORCH_LIBRARY)
+  #
+  set(VLLM_STABLE_EXT_SRC
+    "csrc/libtorch_stable/torch_bindings.cpp")
+
+  if(VLLM_GPU_LANG STREQUAL "CUDA")
+    list(APPEND VLLM_STABLE_EXT_SRC "csrc/libtorch_stable/permute_cols.cu")
+  endif()
+
+  if(VLLM_GPU_LANG STREQUAL "CUDA")
+    set_gencode_flags_for_srcs(
+      SRCS "${VLLM_STABLE_EXT_SRC}"
+      CUDA_ARCHS "${CUDA_ARCHS}")
+  endif()
+
+  message(STATUS "Enabling C_stable extension.")
+  define_extension_target(
+    _C_stable_libtorch
+    DESTINATION vllm
+    LANGUAGE ${VLLM_GPU_LANG}
+    SOURCES ${VLLM_STABLE_EXT_SRC}
+    COMPILE_FLAGS ${VLLM_GPU_FLAGS}
+    ARCHITECTURES ${VLLM_GPU_ARCHES}
+    USE_SABI 3
+    WITH_SOABI)
+
+  # Set TORCH_TARGET_VERSION for stable ABI compatibility.
+  # This ensures we only use C-shim APIs available in PyTorch 2.10.
+  # _C_stable_libtorch is abi compatible with PyTorch >= TORCH_TARGET_VERSION
+  # which is currently set to 2.10.
+  target_compile_definitions(_C_stable_libtorch PRIVATE
+    TORCH_TARGET_VERSION=0x020A000000000000ULL)
+
+  # Needed to use cuda APIs from C-shim
+  target_compile_definitions(_C_stable_libtorch PRIVATE
+    USE_CUDA)
+endif()
+
 #
 # _moe_C extension
 #

csrc/libtorch_stable/ops.h

@@ -0,0 +1,9 @@
+#pragma once
+
+#include <torch/csrc/stable/library.h>
+#include <torch/csrc/stable/tensor.h>
+
+#ifndef USE_ROCM
+torch::stable::Tensor permute_cols(torch::stable::Tensor const& A,
+                                   torch::stable::Tensor const& perm);
+#endif

csrc/libtorch_stable/permute_cols.cu

@@ -1,10 +1,13 @@
-#include <torch/all.h>
-
-#include <ATen/cuda/CUDAContext.h>
-#include <c10/cuda/CUDAGuard.h>
+#include <torch/csrc/stable/library.h>
+#include <torch/csrc/stable/tensor.h>
+#include <torch/csrc/stable/accelerator.h>
+#include <torch/csrc/stable/ops.h>
+#include <torch/headeronly/core/ScalarType.h>
 
 #include <cuda_fp16.h>
 
+#include "torch_utils.h"
+
 static constexpr int default_threads = 256;
 static constexpr int div_ceil(int a, int b) { return (a + b - 1) / b; }
 
@@ -64,19 +67,22 @@ __global__ void permute_cols_kernel(int4 const* __restrict__ a_int4_ptr,
 
 // More efficient version of A[..., perm]
 //  taken from gptq_marlin.cu
-torch::Tensor permute_cols(torch::Tensor const& A, torch::Tensor const& perm) {
-  const at::cuda::OptionalCUDAGuard device_guard(device_of(A));
-  auto dev = A.get_device();
-  auto stream = at::cuda::getCurrentCUDAStream(dev);
+torch::stable::Tensor permute_cols(torch::stable::Tensor const& A,
+                                   torch::stable::Tensor const& perm) {
+  const int32_t dev = A.get_device_index();
+  const torch::stable::accelerator::DeviceGuard device_guard(dev);
+  const auto stream = get_current_cuda_stream(dev);
 
-  TORCH_CHECK(A.scalar_type() == at::kHalf || A.scalar_type() == at::kBFloat16,
-              "Currently only 16bit types are supported");
-  TORCH_CHECK(A.is_contiguous(), "A must be contiguous");
-  TORCH_CHECK(A.size(-1) % 8 == 0,
-              "A columns must be a multiple of 8 (128bits)");
-  auto A_2d = A.view({-1, A.size(-1)});
+  STD_TORCH_CHECK(
+      A.scalar_type() == torch::headeronly::ScalarType::Half ||
+          A.scalar_type() == torch::headeronly::ScalarType::BFloat16,
+      "Currently only 16bit types are supported");
+  STD_TORCH_CHECK(A.is_contiguous(), "A must be contiguous");
+  STD_TORCH_CHECK(A.size(-1) % 8 == 0,
+                  "A columns must be a multiple of 8 (128bits)");
+  auto A_2d = torch::stable::view(A, {-1, A.size(-1)});
 
-  torch::Tensor D = torch::empty_like(A);
+  torch::stable::Tensor D = torch::stable::empty_like(A);
   int sms;
   cudaDeviceGetAttribute(&sms, cudaDevAttrMultiProcessorCount, dev);
   int block_rows = div_ceil(A_2d.size(0), sms);

csrc/libtorch_stable/torch_bindings.cpp

@@ -0,0 +1,21 @@
+#include "ops.h"
+#include "core/registration.h"
+
+#include <torch/csrc/stable/library.h>
+
+// Register ops with STABLE_TORCH_LIBRARY for libtorch stable ABI compatibility.
+// Note: We register under namespace "_C" so ops are accessible as
+// torch.ops._C.<op_name> for compatibility with existing code.
+STABLE_TORCH_LIBRARY_FRAGMENT(_C, m) {
+#ifndef USE_ROCM
+  m.def("permute_cols(Tensor A, Tensor perm) -> Tensor");
+#endif
+}
+
+STABLE_TORCH_LIBRARY_IMPL(_C, CUDA, m) {
+#ifndef USE_ROCM
+  m.impl("permute_cols", TORCH_BOX(&permute_cols));
+#endif
+}
+
+REGISTER_EXTENSION(_C_stable_libtorch)

csrc/libtorch_stable/torch_utils.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#include <torch/csrc/inductor/aoti_torch/c/shim.h>
+#include <cuda_runtime.h>
+
+// Utility to get the current CUDA stream for a given device using stable APIs.
+// Returns a cudaStream_t for use in kernel launches.
+inline cudaStream_t get_current_cuda_stream(int32_t device_index) {
+  void* stream_ptr = nullptr;
+  TORCH_ERROR_CODE_CHECK(
+      aoti_torch_get_current_cuda_stream(device_index, &stream_ptr));
+  return reinterpret_cast<cudaStream_t>(stream_ptr);
+}

csrc/ops.h

@@ -201,7 +201,6 @@ torch::Tensor awq_dequantize(torch::Tensor _kernel,
                              torch::Tensor _zeros, int64_t split_k_iters,
                              int64_t thx, int64_t thy);
 
-torch::Tensor permute_cols(torch::Tensor const& A, torch::Tensor const& perm);
 #endif
 
 torch::Tensor ggml_dequantize(torch::Tensor W, int64_t type, int64_t m,

csrc/torch_bindings.cpp

@@ -303,9 +303,6 @@ TORCH_LIBRARY_EXPAND(TORCH_EXTENSION_NAME, ops) {
       ") -> Tensor");
   // conditionally compiled so impl registration is in source file
 
-  ops.def("permute_cols(Tensor A, Tensor perm) -> Tensor");
-  ops.impl("permute_cols", torch::kCUDA, &permute_cols);
-
   // Marlin Optimized Quantized GEMM (supports GPTQ, AWQ, FP8, NVFP4, MXFP4).
   ops.def(
       "marlin_gemm(Tensor a, Tensor? c_or_none, Tensor b_q_weight, "

setup.py

@@ -597,6 +597,7 @@ class precompiled_wheel_utils:
             with zipfile.ZipFile(wheel_path) as wheel:
                 files_to_copy = [
                     "vllm/_C.abi3.so",
+                    "vllm/_C_stable_libtorch.abi3.so",
                     "vllm/_moe_C.abi3.so",
                     "vllm/_flashmla_C.abi3.so",
                     "vllm/_flashmla_extension_C.abi3.so",
@@ -932,6 +933,10 @@ if _is_cpu():
 
 if _build_custom_ops():
     ext_modules.append(CMakeExtension(name="vllm._C"))
+    # also _is_hip() once https://github.com/vllm-project/vllm/issues/35163 is
+    # fixed
+    if _is_cuda():
+        ext_modules.append(CMakeExtension(name="vllm._C_stable_libtorch"))
 
 package_data = {
     "vllm": [

vllm/platforms/cuda.py

@@ -19,6 +19,7 @@ from typing_extensions import ParamSpec
 
 # import custom ops, trigger op registration
 import vllm._C  # noqa
+import vllm._C_stable_libtorch  # noqa
 from vllm.logger import init_logger
 from vllm.utils.import_utils import import_pynvml
 from vllm.utils.torch_utils import cuda_device_count_stateless