pytorch/torch/csrc/distributed/c10d/default_comm_hooks.cpp
Rohan Varma f0f5cffde9 [DDP] Add a debug check in cpp fp16 compress (#63379)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63379

this codepath has been prone to bugs as seen in the below diff, this
will help ensure against changes/refactors that touch this, as a basic sanity
check. Enabled it in debug-only builds to not affect the perf.
ghstack-source-id: 136056093

Test Plan: CI

Reviewed By: SciPioneer

Differential Revision: D30358440

fbshipit-source-id: e1b3893a223722c2593ceed8696a09c7d07d47c1
2021-08-18 11:51:19 -07:00

54 lines
1.8 KiB
C++

#include <c10d/default_comm_hooks.hpp>
#include <c10/core/ScalarType.h>
#include <c10/util/Exception.h>
#include <c10d/ProcessGroup.hpp>
#include <c10d/comm.hpp>
#include <torch/torch.h>
namespace c10d {
c10::intrusive_ptr<c10::ivalue::Future> AllReduceCommHook::runHook(
GradBucket& bucket) {
std::vector<at::Tensor> tensors = {bucket.getBufferRef()};
// Apply the division first to avoid overflow, especially for FP16.
tensors[0] /= state_->getSize();
return state_->allreduce(tensors)->getFuture();
}
c10::intrusive_ptr<c10::ivalue::Future> FP16CompressCommHook::runHook(
GradBucket& bucket) {
auto compressed_tensor = bucket.getBufferRef().to(torch::kFloat16);
// Apply the division first to avoid overflow.
compressed_tensor /= state_->getSize();
std::vector<at::Tensor> tensors = {compressed_tensor};
auto allreduce_fut = state_->allreduce(tensors)->getFuture();
auto decompressed_tensor = bucket.getBufferRef();
auto decompress = [decompressed_tensor](c10::ivalue::Future& allreduce_fut) {
auto result = allreduce_fut.value();
TORCH_INTERNAL_ASSERT(
result.isTensorList(),
"ProcessGroup::allreduce should return TensorList");
auto reduce_tensor = result.toTensorVector()[0];
TORCH_INTERNAL_ASSERT_DEBUG_ONLY(
reduce_tensor.scalar_type() == at::ScalarType::Half,
"Expected reduced tensor to be fp16 in FP16CompressHook, but got type ",
reduce_tensor.scalar_type()
);
decompressed_tensor.copy_(reduce_tensor);
return c10::IValue(decompressed_tensor);
};
return allreduce_fut->then(decompress, allreduce_fut->elementType());
}
c10::intrusive_ptr<c10::ivalue::Future> _AllReduceBySumCommHook::
runHook(GradBucket& bucket) {
std::vector<at::Tensor> tensors = {bucket.getBufferRef()};
return state_->allreduce(tensors)->getFuture();
}
} // namespace c10d