fix comments and run linter

torch_xla/csrc/dl_convertor.cpp

@@ -52,13 +52,15 @@ DLDeviceType DLDeviceTypeForDevice(const xla::PjRtDevice& device) {
               << " cannot be used as a DLPack device.";
 }
 
+// Reference: https://github.com/openxla/xla/blob/main/xla/python/dlpack.cc
 DLDevice DLDeviceForDevice(const xla::PjRtDevice& device) {
   DLDevice dlDevice;
   dlDevice.device_type = DLDeviceTypeForDevice(device);
   dlDevice.device_id = device.local_hardware_id();
   return dlDevice;
 }
 
+// Reference: https://github.com/openxla/xla/blob/main/xla/python/dlpack.cc
 DLDataType PrimitiveTypeToDLDataType(xla::PrimitiveType type) {
   switch (type) {
     case xla::PrimitiveType::S8:
@@ -161,6 +163,7 @@ DLManagedTensor* toDLPack(const at::Tensor& input) {
   return &(pack.release()->tensor);
 }
 
+// Reference: https://github.com/openxla/xla/blob/main/xla/python/dlpack.cc
 absl::StatusOr<xla::PjRtDevice*> DeviceForDLDevice(const DLDevice& context) {
   switch (context.device_type) {
     case DLDeviceType::kDLCPU:
@@ -262,6 +265,7 @@ absl::StatusOr<xla::PrimitiveType> DLDataTypeToPrimitiveType(DLDataType type) {
   }
 }
 
+// Reference: https://github.com/openxla/xla/blob/main/xla/python/dlpack.cc
 absl::StatusOr<std::vector<int64_t>> StridesToLayout(
     absl::Span<int64_t const> dims, absl::Span<int64_t const> strides) {
   XLA_CHECK_EQ(dims.size(), strides.size());

torch_xla/csrc/init_python_bindings.cpp

@@ -2541,19 +2541,24 @@ void InitXlaModuleBindings(py::module m) {
         });
 
   // from an XLA tensor to a dlpack tensor.
+  // If ext_data is the result of an CUDA computation, we should synchronize
+  // (waits for all kernels in all streams on a CUDA device to complete) if the
+  // current stream is different from the ext_data's stream. Otherwise, we may
+  // risk of getting incorrect results.
   m.def("_to_dlpack", [](const at::Tensor& input) -> py::handle {
     DLManagedTensor* dlMTensor;
     {
       NoGilSection nogil;
       dlMTensor = torch_xla::toDLPack(input);
     }
-    // return py::reinterpret_steal<py::object>(PyCapsule_New(dlMTensor,
-    // "dltensor", dlPack_Capsule_Destructor));
     return PyCapsule_New(dlMTensor, "dltensor", dlPack_Capsule_Destructor);
   });
-  // m.def("_to_dlpack", &tensor_toDLPack, ""); //
 
   // from a dlpack tensor to an XLA tensor
+  // If ext_data is the result of an CUDA computation, we should synchronize
+  // (waits for all kernels in all streams on a CUDA device to complete) if the
+  // current stream is different from the ext_data's stream. Otherwise, we may
+  // risk of getting incorrect results.
   m.def("_from_dlpack", [](py::handle ext_data) -> at::Tensor {
     return tensor_fromDLPack(ext_data.ptr());
   });