| /* |
| * Copyright (c) 2020 Arm Limited. All rights reserved. |
| * |
| * SPDX-License-Identifier: Apache-2.0 |
| * |
| * Licensed under the Apache License, Version 2.0 (the License); you may |
| * not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an AS IS BASIS, WITHOUT |
| * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| * |
| * Description: |
| * Declaration of the search-based allocator. |
| */ |
| |
| #ifndef __SEARCH_ALLOCATOR_H |
| #define __SEARCH_ALLOCATOR_H |
| |
| #include <algorithm> |
| #include <cstdint> |
| #include <random> |
| #include <set> |
| #include <vector> |
| |
| /** |
| * Live range |
| */ |
| struct LiveRange { |
| /** Start time (input to the allocator algorithm) */ |
| uint32_t start_time; |
| /** End time, inclusive (input to the allocator algorithm) */ |
| uint32_t end_time; |
| /** Size in bytes (input to the allocator algorithm) */ |
| uint32_t size; |
| /** Index of this live range */ |
| int id; |
| /** Allocated address (the main output from the allocator algorithm) */ |
| uint32_t address; |
| /** End address, exclusive */ |
| uint32_t end_address; |
| /** id of predecessor live range (predecessor's end address == this lr's address) */ |
| int predecessor; |
| /** Turn at which the live range was allocated */ |
| size_t turn; |
| |
| bool overlaps(uint32_t addr2, uint32_t size2) const { |
| return address < addr2 + size2 && addr2 < end_address; |
| } |
| bool is_neighbour(const LiveRange &lr) const { |
| return start_time <= lr.end_time && lr.start_time <= end_time; |
| } |
| }; |
| |
| /** |
| * Implements tensor allocator using state space exploration. |
| * |
| * The basic algorithm is: |
| * |
| * Use a heuristic allocator to find an initial allocation |
| * while allocation is not optimal and iterations < MAX_ITERATIONS { |
| * find the "bottleneck": the live range with highest end address |
| * find all live ranges that affected the allocation of the bottleneck |
| * swap the order of any two affecting live ranges |
| * reallocate tensors using the reordered live ranges |
| * if the new allocation is better: keep it, else set allocation to previous allocation |
| * } |
| */ |
| class SearchAllocator { |
| private: |
| static constexpr int MAX_ITERATIONS = 500; |
| static constexpr uint32_t NOT_ALLOCATED = UINT32_MAX; |
| /** Used for live ranges allocated at address 0 */ |
| static constexpr int NO_PREDECESSOR = -1; |
| /** Contains the live ranges */ |
| std::vector<LiveRange> lrs; |
| /** Contains active live ranges at each timestamp */ |
| std::vector<std::vector<LiveRange*>> lrs_at_time; |
| /** |
| * Contains neighbours of each live range (indexed by lr.id), i.e. |
| * live ranges with overlapping start/end time. |
| */ |
| std::vector<std::vector<LiveRange*>> neighbours; |
| /** |
| * At each timestamp: accumulated size of active live ranges |
| */ |
| std::vector<uint32_t> size_at_time; |
| /** |
| * For each live range: max value of size_at_time (only used in the heuristic allocation) |
| */ |
| std::vector<uint32_t> lr_urgency; |
| /** |
| * The minimum possible size, assuming all live ranges can be perfectly allocated |
| */ |
| uint32_t min_required_size; |
| /** The algorithm stops once the target size has been achieved */ |
| uint32_t target_size; |
| /** The highest end address of the best found allocation */ |
| uint32_t best_size; |
| /** Number of performed iterations */ |
| size_t nr_iterations = 0; |
| /** Random number generator; use default seed (which is well-defined) */ |
| std::mt19937 rng; |
| public: |
| SearchAllocator(const std::vector<LiveRange> &live_ranges, uint32_t size_limit); |
| /** |
| * Runs the allocation algorithm. Finishes when the target size has been |
| * reached or when maximum iterations have been run. |
| * The allocated addresses are placed in the output vector, in the same |
| * order as the input vector. |
| * |
| * Implementation note: the algorithm produces reproduceable results by using |
| * a well-defined random number generator with well-defined default seed, |
| * and using a fixed number of iterations. |
| */ |
| uint32_t allocate(std::vector<uint32_t> &output); |
| uint32_t get_min_required_size() const { |
| return min_required_size; |
| } |
| size_t get_nr_iterations() const { |
| return nr_iterations; |
| } |
| private: |
| /** |
| * Allocates the given live range at the smallest possible address |
| */ |
| void allocate_lr(LiveRange &lr) const; |
| /** |
| * Allocates the live ranges in the order indicated by the indices; |
| * allocates each live range at the lowest possible address. |
| */ |
| uint32_t allocate_indices(const std::vector<size_t> &indices); |
| /** Sorts live ranges based on heuristics, used for the initial allocation */ |
| void sort_indices_on_prio(std::vector<size_t> &indices) const; |
| /** Adds the given live range + predecessors to the turns vector */ |
| void add_predecessor_turns(std::set<size_t> &turns, const LiveRange &lr) const; |
| /** |
| * Finds the "bottleneck", the live range with highest end address, and reorders the indices |
| * such that a next allocation might lower the memory usage. |
| * |
| * --------- |
| * | | |
| * | D | |
| * | | |
| * ---------------------------------- |
| * | B | |
| * ------------------------------- |
| * | | |
| * |A| --- |
| * | | |C| |
| * | | | | |
| * --------------------------------------- |
| * |
| * In the above example, the allocation order was [A, B, C, D] and D is the resulting bottle-neck. |
| * The live ranges that affected the allocation of D are the direct neighbours of D (i.e. B and C), |
| * and all direct and indirect predecessors of D and its neighbours |
| * (i.e. A, which is the predecessor of B, and indirect predecessor of D). |
| * |
| * By permuting the order in which the affecting live ranges are allocated, the bottleneck might |
| * be lowered. In the above example, almost any permutation would lower the bottleneck. |
| * |
| * Note that there is room to improve the efficiency of the algorithm. |
| * One way could be to first allocate all direct neighbours of the bottleneck |
| * (i.e. B, C, D) and then the other affecting live ranges (i.e. A). The algorithm currently does |
| * not actively try this, as it may lead to allocation loops (A could become the new bottle-neck); |
| * it just uses a higher probability of selecting A. |
| */ |
| void attempt_bottleneck_fix(std::vector<size_t> &indices); |
| /** Search for a solution, using the given indices as initial solution. */ |
| void search(std::vector<size_t> &indices, uint32_t initial_size, int iterations); |
| }; |
| |
| /** Wrapper function to perform live range allocation */ |
| uint32_t allocate(const std::vector<uint32_t> &input, int available_size, std::vector<uint32_t> &output); |
| |
| #endif // __SEARCH_ALLOCATOR_H |