| // -*- C++ -*- |
| |
| // Copyright (C) 2007-2020 Free Software Foundation, Inc. |
| // |
| // This file is part of the GNU ISO C++ Library. This library is free |
| // software; you can redistribute it and/or modify it under the terms |
| // of the GNU General Public License as published by the Free Software |
| // Foundation; either version 3, or (at your option) any later |
| // version. |
| |
| // This library is distributed in the hope that it will be useful, but |
| // WITHOUT ANY WARRANTY; without even the implied warranty of |
| // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| // General Public License for more details. |
| |
| // Under Section 7 of GPL version 3, you are granted additional |
| // permissions described in the GCC Runtime Library Exception, version |
| // 3.1, as published by the Free Software Foundation. |
| |
| // You should have received a copy of the GNU General Public License and |
| // a copy of the GCC Runtime Library Exception along with this program; |
| // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see |
| // <http://www.gnu.org/licenses/>. |
| |
| /** @file parallel/settings.h |
| * @brief Runtime settings and tuning parameters, heuristics to decide |
| * whether to use parallelized algorithms. |
| * |
| * This file is a GNU parallel extension to the Standard C++ Library. |
| * |
| * @section parallelization_decision Deciding whether to run an algorithm in parallel. |
| * |
| * There are several ways the user can switch on and off the parallel |
| * execution of an algorithm, both at compile- and run-time. |
| * |
| * Only sequential execution can be forced at compile-time. This |
| * reduces code size and protects code parts that have |
| * non-thread-safe side effects. |
| * |
| * Ultimately, forcing parallel execution at compile-time makes |
| * sense. Often, the sequential algorithm implementation is used as |
| * a subroutine, so no reduction in code size can be achieved. Also, |
| * the machine the program is run on might have only one processor |
| * core, so to avoid overhead, the algorithm is executed |
| * sequentially. |
| * |
| * To force sequential execution of an algorithm ultimately at |
| * compile-time, the user must add the tag |
| * gnu_parallel::sequential_tag() to the end of the parameter list, |
| * e. g. |
| * |
| * \code |
| * std::sort(__v.begin(), __v.end(), __gnu_parallel::sequential_tag()); |
| * \endcode |
| * |
| * This is compatible with all overloaded algorithm variants. No |
| * additional code will be instantiated, at all. The same holds for |
| * most algorithm calls with iterators not providing random access. |
| * |
| * If the algorithm call is not forced to be executed sequentially |
| * at compile-time, the decision is made at run-time. |
| * The global variable __gnu_parallel::_Settings::algorithm_strategy |
| * is checked. It is a tristate variable corresponding to: |
| * - a. force_sequential, meaning the sequential algorithm is executed. |
| * - b. force_parallel, meaning the parallel algorithm is executed. |
| * - c. heuristic |
| * |
| * For heuristic, the parallel algorithm implementation is called |
| * only if the input size is sufficiently large. For most |
| * algorithms, the input size is the (combined) length of the input |
| * sequence(__s). The threshold can be set by the user, individually |
| * for each algorithm. The according variables are called |
| * gnu_parallel::_Settings::[algorithm]_minimal_n . |
| * |
| * For some of the algorithms, there are even more tuning options, |
| * e. g. the ability to choose from multiple algorithm variants. See |
| * below for details. |
| */ |
| |
| // Written by Johannes Singler and Felix Putze. |
| |
| #ifndef _GLIBCXX_PARALLEL_SETTINGS_H |
| #define _GLIBCXX_PARALLEL_SETTINGS_H 1 |
| |
| #include <parallel/types.h> |
| |
| /** |
| * @brief Determine at compile(?)-time if the parallel variant of an |
| * algorithm should be called. |
| * @param __c A condition that is convertible to bool that is overruled by |
| * __gnu_parallel::_Settings::algorithm_strategy. Usually a decision |
| * based on the input size. |
| */ |
| #define _GLIBCXX_PARALLEL_CONDITION(__c) \ |
| (__gnu_parallel::_Settings::get().algorithm_strategy \ |
| != __gnu_parallel::force_sequential \ |
| && ((__gnu_parallel::__get_max_threads() > 1 && (__c)) \ |
| || __gnu_parallel::_Settings::get().algorithm_strategy \ |
| == __gnu_parallel::force_parallel)) |
| |
| /* |
| inline bool |
| parallel_condition(bool __c) |
| { |
| bool ret = false; |
| const _Settings& __s = _Settings::get(); |
| if (__s.algorithm_strategy != force_seqential) |
| { |
| if (__s.algorithm_strategy == force_parallel) |
| ret = true; |
| else |
| ret = __get_max_threads() > 1 && __c; |
| } |
| return ret; |
| } |
| */ |
| |
| namespace __gnu_parallel |
| { |
| /// class _Settings |
| /// Run-time settings for the parallel mode including all tunable parameters. |
| struct _Settings |
| { |
| _AlgorithmStrategy algorithm_strategy; |
| |
| _SortAlgorithm sort_algorithm; |
| _PartialSumAlgorithm partial_sum_algorithm; |
| _MultiwayMergeAlgorithm multiway_merge_algorithm; |
| _FindAlgorithm find_algorithm; |
| |
| _SplittingAlgorithm sort_splitting; |
| _SplittingAlgorithm merge_splitting; |
| _SplittingAlgorithm multiway_merge_splitting; |
| |
| // Per-algorithm settings. |
| |
| /// Minimal input size for accumulate. |
| _SequenceIndex accumulate_minimal_n; |
| |
| /// Minimal input size for adjacent_difference. |
| unsigned int adjacent_difference_minimal_n; |
| |
| /// Minimal input size for count and count_if. |
| _SequenceIndex count_minimal_n; |
| |
| /// Minimal input size for fill. |
| _SequenceIndex fill_minimal_n; |
| |
| /// Block size increase factor for find. |
| double find_increasing_factor; |
| |
| /// Initial block size for find. |
| _SequenceIndex find_initial_block_size; |
| |
| /// Maximal block size for find. |
| _SequenceIndex find_maximum_block_size; |
| |
| /// Start with looking for this many elements sequentially, for find. |
| _SequenceIndex find_sequential_search_size; |
| |
| /// Minimal input size for for_each. |
| _SequenceIndex for_each_minimal_n; |
| |
| /// Minimal input size for generate. |
| _SequenceIndex generate_minimal_n; |
| |
| /// Minimal input size for max_element. |
| _SequenceIndex max_element_minimal_n; |
| |
| /// Minimal input size for merge. |
| _SequenceIndex merge_minimal_n; |
| |
| /// Oversampling factor for merge. |
| unsigned int merge_oversampling; |
| |
| /// Minimal input size for min_element. |
| _SequenceIndex min_element_minimal_n; |
| |
| /// Minimal input size for multiway_merge. |
| _SequenceIndex multiway_merge_minimal_n; |
| |
| /// Oversampling factor for multiway_merge. |
| int multiway_merge_minimal_k; |
| |
| /// Oversampling factor for multiway_merge. |
| unsigned int multiway_merge_oversampling; |
| |
| /// Minimal input size for nth_element. |
| _SequenceIndex nth_element_minimal_n; |
| |
| /// Chunk size for partition. |
| _SequenceIndex partition_chunk_size; |
| |
| /// Chunk size for partition, relative to input size. If > 0.0, |
| /// this value overrides partition_chunk_size. |
| double partition_chunk_share; |
| |
| /// Minimal input size for partition. |
| _SequenceIndex partition_minimal_n; |
| |
| /// Minimal input size for partial_sort. |
| _SequenceIndex partial_sort_minimal_n; |
| |
| /// Ratio for partial_sum. Assume "sum and write result" to be |
| /// this factor slower than just "sum". |
| float partial_sum_dilation; |
| |
| /// Minimal input size for partial_sum. |
| unsigned int partial_sum_minimal_n; |
| |
| /// Minimal input size for random_shuffle. |
| unsigned int random_shuffle_minimal_n; |
| |
| /// Minimal input size for replace and replace_if. |
| _SequenceIndex replace_minimal_n; |
| |
| /// Minimal input size for set_difference. |
| _SequenceIndex set_difference_minimal_n; |
| |
| /// Minimal input size for set_intersection. |
| _SequenceIndex set_intersection_minimal_n; |
| |
| /// Minimal input size for set_symmetric_difference. |
| _SequenceIndex set_symmetric_difference_minimal_n; |
| |
| /// Minimal input size for set_union. |
| _SequenceIndex set_union_minimal_n; |
| |
| /// Minimal input size for parallel sorting. |
| _SequenceIndex sort_minimal_n; |
| |
| /// Oversampling factor for parallel std::sort (MWMS). |
| unsigned int sort_mwms_oversampling; |
| |
| /// Such many samples to take to find a good pivot (quicksort). |
| unsigned int sort_qs_num_samples_preset; |
| |
| /// Maximal subsequence __length to switch to unbalanced __base case. |
| /// Applies to std::sort with dynamically load-balanced quicksort. |
| _SequenceIndex sort_qsb_base_case_maximal_n; |
| |
| /// Minimal input size for parallel std::transform. |
| _SequenceIndex transform_minimal_n; |
| |
| /// Minimal input size for unique_copy. |
| _SequenceIndex unique_copy_minimal_n; |
| |
| _SequenceIndex workstealing_chunk_size; |
| |
| // Hardware dependent tuning parameters. |
| |
| /// size of the L1 cache in bytes (underestimation). |
| unsigned long long L1_cache_size; |
| |
| /// size of the L2 cache in bytes (underestimation). |
| unsigned long long L2_cache_size; |
| |
| /// size of the Translation Lookaside Buffer (underestimation). |
| unsigned int TLB_size; |
| |
| /// Overestimation of cache line size. Used to avoid false |
| /// sharing, i.e. elements of different threads are at least this |
| /// amount apart. |
| unsigned int cache_line_size; |
| |
| // Statistics. |
| |
| /// The number of stolen ranges in load-balanced quicksort. |
| _SequenceIndex qsb_steals; |
| |
| /// Minimal input size for search and search_n. |
| _SequenceIndex search_minimal_n; |
| |
| /// Block size scale-down factor with respect to current position. |
| float find_scale_factor; |
| |
| /// Get the global settings. |
| _GLIBCXX_CONST static const _Settings& |
| get() throw(); |
| |
| /// Set the global settings. |
| static void |
| set(_Settings&) throw(); |
| |
| explicit |
| _Settings() : |
| algorithm_strategy(heuristic), |
| sort_algorithm(MWMS), |
| partial_sum_algorithm(LINEAR), |
| multiway_merge_algorithm(LOSER_TREE), |
| find_algorithm(CONSTANT_SIZE_BLOCKS), |
| sort_splitting(EXACT), |
| merge_splitting(EXACT), |
| multiway_merge_splitting(EXACT), |
| accumulate_minimal_n(1000), |
| adjacent_difference_minimal_n(1000), |
| count_minimal_n(1000), |
| fill_minimal_n(1000), |
| find_increasing_factor(2.0), |
| find_initial_block_size(256), |
| find_maximum_block_size(8192), |
| find_sequential_search_size(256), |
| for_each_minimal_n(1000), |
| generate_minimal_n(1000), |
| max_element_minimal_n(1000), |
| merge_minimal_n(1000), |
| merge_oversampling(10), |
| min_element_minimal_n(1000), |
| multiway_merge_minimal_n(1000), |
| multiway_merge_minimal_k(2), multiway_merge_oversampling(10), |
| nth_element_minimal_n(1000), |
| partition_chunk_size(1000), |
| partition_chunk_share(0.0), |
| partition_minimal_n(1000), |
| partial_sort_minimal_n(1000), |
| partial_sum_dilation(1.0f), |
| partial_sum_minimal_n(1000), |
| random_shuffle_minimal_n(1000), |
| replace_minimal_n(1000), |
| set_difference_minimal_n(1000), |
| set_intersection_minimal_n(1000), |
| set_symmetric_difference_minimal_n(1000), |
| set_union_minimal_n(1000), |
| sort_minimal_n(1000), |
| sort_mwms_oversampling(10), |
| sort_qs_num_samples_preset(100), |
| sort_qsb_base_case_maximal_n(100), |
| transform_minimal_n(1000), |
| unique_copy_minimal_n(10000), |
| workstealing_chunk_size(100), |
| L1_cache_size(16 << 10), |
| L2_cache_size(256 << 10), |
| TLB_size(128), |
| cache_line_size(64), |
| qsb_steals(0), |
| search_minimal_n(1000), |
| find_scale_factor(0.01f) |
| { } |
| }; |
| } |
| |
| #endif /* _GLIBCXX_PARALLEL_SETTINGS_H */ |