/* Copyright 2019 The TensorFlow Authors. All Rights Reserved.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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==============================================================================*/
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#ifndef TENSORFLOW_COMPILER_JIT_CLONE_CONSTANTS_FOR_BETTER_CLUSTERING_H_
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#define TENSORFLOW_COMPILER_JIT_CLONE_CONSTANTS_FOR_BETTER_CLUSTERING_H_
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#include "tensorflow/core/common_runtime/optimization_registry.h"
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#include "absl/container/flat_hash_set.h"
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#include "tensorflow/stream_executor/lib/statusor.h"
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namespace tensorflow {
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// Clones small host constants in the graph to make it easier to form larger
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// clusters.
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//
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// This helps us in two ways:
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//
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// - It reduces dependencies between clusters. Let's say a constant C is used
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// by nodes X and Y. If X and Y are put in different clusters (for whatever
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// reason) Y's cluster now has to wait for all the operations in X's cluster
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// to finish before it starts running.
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//
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// - It lets us create bigger clusters in multi-GPU benchmarks. Consider the
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// following graph:
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//
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// digraph {
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// Const -> GPU_1
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// Const -> GPU_0_Y
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// GPU_0_X -> GPU_0_Y
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// }
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//
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// We'd cluster Const and GPU_1 together (and place it on GPU_1), and this
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// will block us from clustering GPU_0_X and GPU_0_Y together since that
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// would increase the amount of work on GPU 0 waiting on work on GPU 1.
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// However, cloning Const into two copies, one for GPU_0_Y and one for GPU_1
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// will let us create one cluster containing {Const/copy_0, GPU_1} and
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// another containing {Const/copy_1, GPU_0_X, GPU_0_Y}.
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//
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// We only clone small host constants now to avoid increasing memory consumption
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// too much. Moreover, in practice the constants we have to duplicate are
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// things like the `perm` input to `Transpose` and the `size` input to `Slice`
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// which tend to be small anyway.
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class CloneConstantsForBetterClusteringPass : public GraphOptimizationPass {
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public:
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CloneConstantsForBetterClusteringPass() = default;
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Status Run(const GraphOptimizationPassOptions& options) override;
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private:
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Status CloneSmallHostConstantInputs(
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Graph* g, const absl::flat_hash_set<string>& name_set, Node* n);
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string GenerateUniqueName(const absl::flat_hash_set<string>& name_set,
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absl::string_view prefix);
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se::port::StatusOr<Node*> CloneNode(
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Graph* g, const absl::flat_hash_set<string>& name_set, Node* n);
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int unique_name_counter_ = 0;
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};
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} // namespace tensorflow
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#endif // TENSORFLOW_COMPILER_JIT_CLONE_CONSTANTS_FOR_BETTER_CLUSTERING_H_
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