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@ -24,11 +24,31 @@ static constexpr size_t kDoubleBufferSize = 2;
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class DoubleBufferReader : public framework::DecoratedReader {
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public:
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explicit DoubleBufferReader(ReaderBase* reader)
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: DecoratedReader(reader),
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buffer_(framework::MakeChannel<std::vector<framework::LoDTensor>>(
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kDoubleBufferSize)) {
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std::thread prefetch(&DoubleBufferReader::PrefetchThreadFunc, this);
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struct Item {
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Item() : ctx_(nullptr) {}
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std::vector<framework::LoDTensor> payloads_;
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platform::DeviceContext* ctx_;
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};
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explicit DoubleBufferReader(
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ReaderBase* reader, platform::Place target_place = platform::CPUPlace())
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: DecoratedReader(reader), place_(target_place) {
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for (size_t i = 0; i < kDoubleBufferSize; ++i) {
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if (platform::is_gpu_place(place_)) {
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#ifdef PADDLE_WITH_CUDA
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ctxs_.emplace_back(new platform::CUDADeviceContext(
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boost::get<platform::CUDAPlace>(place_)));
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#endif
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}
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}
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start_thread();
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}
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void start_thread() {
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buffer_ = framework::MakeChannel<Item>(kDoubleBufferSize);
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std::thread prefetch([this] { PrefetchThreadFunc(); });
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prefetch.detach();
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}
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@ -42,7 +62,10 @@ class DoubleBufferReader : public framework::DecoratedReader {
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private:
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void PrefetchThreadFunc();
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framework::Channel<std::vector<framework::LoDTensor>>* buffer_;
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framework::Channel<Item>* buffer_;
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platform::Place place_;
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std::vector<std::unique_ptr<platform::DeviceContext>> ctxs_;
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mutable Item local_buffer_;
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};
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class CreateDoubleBufferReaderOp : public framework::OperatorBase {
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@ -56,7 +79,20 @@ class CreateDoubleBufferReaderOp : public framework::OperatorBase {
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->Get<framework::ReaderHolder>();
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auto* out = scope.FindVar(Output("Out"))
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->template GetMutable<framework::ReaderHolder>();
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out->Reset(new DoubleBufferReader(underlying_reader.Get()));
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auto place_str = Attr<std::string>("place");
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platform::Place place;
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if (place_str == "CPU") {
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place = platform::CPUPlace();
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} else {
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std::istringstream sin(place_str);
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sin.seekg(std::string("CUDA:").size(), std::ios::beg);
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size_t num;
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sin >> num;
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place = platform::CUDAPlace(static_cast<int>(num));
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}
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out->Reset(new DoubleBufferReader(underlying_reader.Get(), place));
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}
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};
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@ -71,44 +107,73 @@ class CreateDoubleBufferReaderOpMaker : public DecoratedReaderMakerBase {
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It launches another thread to execute the 'underlying reader' asynchronously,
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which prevents reading process from blocking subsequent training.
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)DOC");
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std::unordered_set<std::string> enum_range;
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constexpr size_t kMaxCUDADevs = 128;
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for (size_t i = 0; i < kMaxCUDADevs; ++i) {
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enum_range.insert(string::Sprintf("CUDA:%d", i));
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}
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enum_range.insert("CPU");
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AddAttr<std::string>("place", "The double buffer place, default is CPU")
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.SetDefault("CPU")
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.InEnum({enum_range});
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}
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};
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void DoubleBufferReader::ReadNext(std::vector<framework::LoDTensor>* out) {
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out->clear();
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buffer_->Receive(out);
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if (local_buffer_.payloads_.empty()) {
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buffer_->Receive(&local_buffer_);
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}
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*out = local_buffer_.payloads_;
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local_buffer_.payloads_.clear();
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if (local_buffer_.ctx_) {
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local_buffer_.ctx_->Wait();
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}
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}
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void DoubleBufferReader::ReInit() {
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reader_->ReInit();
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buffer_->Close();
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// The existing prefetch thread will terminate for the buffer_ is closed.
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buffer_ = framework::MakeChannel<std::vector<framework::LoDTensor>>(
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kDoubleBufferSize);
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std::thread prefetch(&DoubleBufferReader::PrefetchThreadFunc, this);
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prefetch.detach();
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start_thread();
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}
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void DoubleBufferReader::PrefetchThreadFunc() {
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VLOG(5) << "A new prefetch thread starts.";
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while (true) {
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std::vector<framework::LoDTensor> batch;
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reader_->ReadNext(&batch);
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if (batch.empty()) {
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// EOF
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buffer_->Close();
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VLOG(5) << "Reached the end of the file. The prefetch thread terminates.";
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break;
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size_t gpu_ctx_offset = 0;
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while (reader_->HasNext()) {
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Item batch;
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reader_->ReadNext(&batch.payloads_);
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if (platform::is_gpu_place(place_)) {
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std::vector<framework::LoDTensor> gpu_batch;
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auto& gpu_ctx = this->ctxs_[gpu_ctx_offset++];
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gpu_ctx_offset %= this->ctxs_.size();
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gpu_batch.resize(batch.payloads_.size());
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for (size_t i = 0; i < batch.payloads_.size(); ++i) {
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framework::TensorCopy(batch.payloads_[i], place_, *gpu_ctx,
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&gpu_batch[i]);
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gpu_batch[i].set_lod(batch.payloads_[i].lod());
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}
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batch.ctx_ = gpu_ctx.get();
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std::swap(gpu_batch, batch.payloads_);
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}
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if (!buffer_->Send(&batch)) {
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VLOG(5) << "WARNING: The double buffer channel has been closed. The "
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"prefetch thread terminates.";
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break;
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}
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}
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buffer_->Close();
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}
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bool DoubleBufferReader::HasNext() const { PADDLE_THROW("Not Implemented"); }
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bool DoubleBufferReader::HasNext() const {
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if (local_buffer_.payloads_.empty()) {
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bool ok = buffer_->Receive(&local_buffer_);
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return ok;
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} else {
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return true;
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}
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}
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} // namespace reader
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} // namespace operators
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