343 lines
12 KiB
C++
343 lines
12 KiB
C++
// -*- C++ -*-
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// Copyright (C) 2007-2019 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the terms
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// of the GNU General Public License as published by the Free Software
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// Foundation; either version 3, or (at your option) any later
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// version.
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// This library is distributed in the hope that it will be useful, but
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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// General Public License for more details.
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// Under Section 7 of GPL version 3, you are granted additional
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// permissions described in the GCC Runtime Library Exception, version
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// 3.1, as published by the Free Software Foundation.
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// You should have received a copy of the GNU General Public License and
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// a copy of the GCC Runtime Library Exception along with this program;
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// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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// <http://www.gnu.org/licenses/>.
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/** @file parallel/settings.h
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* @brief Runtime settings and tuning parameters, heuristics to decide
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* whether to use parallelized algorithms.
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*
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* This file is a GNU parallel extension to the Standard C++ Library.
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*
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* @section parallelization_decision Deciding whether to run an algorithm in parallel.
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*
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* There are several ways the user can switch on and off the parallel
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* execution of an algorithm, both at compile- and run-time.
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*
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* Only sequential execution can be forced at compile-time. This
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* reduces code size and protects code parts that have
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* non-thread-safe side effects.
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*
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* Ultimately, forcing parallel execution at compile-time makes
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* sense. Often, the sequential algorithm implementation is used as
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* a subroutine, so no reduction in code size can be achieved. Also,
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* the machine the program is run on might have only one processor
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* core, so to avoid overhead, the algorithm is executed
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* sequentially.
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*
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* To force sequential execution of an algorithm ultimately at
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* compile-time, the user must add the tag
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* gnu_parallel::sequential_tag() to the end of the parameter list,
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* e. g.
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*
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* \code
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* std::sort(__v.begin(), __v.end(), __gnu_parallel::sequential_tag());
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* \endcode
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*
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* This is compatible with all overloaded algorithm variants. No
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* additional code will be instantiated, at all. The same holds for
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* most algorithm calls with iterators not providing random access.
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*
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* If the algorithm call is not forced to be executed sequentially
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* at compile-time, the decision is made at run-time.
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* The global variable __gnu_parallel::_Settings::algorithm_strategy
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* is checked. It is a tristate variable corresponding to:
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* - a. force_sequential, meaning the sequential algorithm is executed.
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* - b. force_parallel, meaning the parallel algorithm is executed.
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* - c. heuristic
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*
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* For heuristic, the parallel algorithm implementation is called
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* only if the input size is sufficiently large. For most
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* algorithms, the input size is the (combined) length of the input
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* sequence(__s). The threshold can be set by the user, individually
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* for each algorithm. The according variables are called
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* gnu_parallel::_Settings::[algorithm]_minimal_n .
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*
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* For some of the algorithms, there are even more tuning options,
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* e. g. the ability to choose from multiple algorithm variants. See
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* below for details.
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*/
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// Written by Johannes Singler and Felix Putze.
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#ifndef _GLIBCXX_PARALLEL_SETTINGS_H
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#define _GLIBCXX_PARALLEL_SETTINGS_H 1
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#include <parallel/types.h>
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/**
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* @brief Determine at compile(?)-time if the parallel variant of an
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* algorithm should be called.
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* @param __c A condition that is convertible to bool that is overruled by
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* __gnu_parallel::_Settings::algorithm_strategy. Usually a decision
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* based on the input size.
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*/
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#define _GLIBCXX_PARALLEL_CONDITION(__c) \
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(__gnu_parallel::_Settings::get().algorithm_strategy \
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!= __gnu_parallel::force_sequential \
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&& ((__gnu_parallel::__get_max_threads() > 1 && (__c)) \
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|| __gnu_parallel::_Settings::get().algorithm_strategy \
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== __gnu_parallel::force_parallel))
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/*
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inline bool
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parallel_condition(bool __c)
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{
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bool ret = false;
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const _Settings& __s = _Settings::get();
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if (__s.algorithm_strategy != force_seqential)
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{
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if (__s.algorithm_strategy == force_parallel)
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ret = true;
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else
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ret = __get_max_threads() > 1 && __c;
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}
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return ret;
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}
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*/
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namespace __gnu_parallel
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{
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/// class _Settings
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/// Run-time settings for the parallel mode including all tunable parameters.
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struct _Settings
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{
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_AlgorithmStrategy algorithm_strategy;
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_SortAlgorithm sort_algorithm;
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_PartialSumAlgorithm partial_sum_algorithm;
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_MultiwayMergeAlgorithm multiway_merge_algorithm;
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_FindAlgorithm find_algorithm;
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_SplittingAlgorithm sort_splitting;
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_SplittingAlgorithm merge_splitting;
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_SplittingAlgorithm multiway_merge_splitting;
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// Per-algorithm settings.
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/// Minimal input size for accumulate.
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_SequenceIndex accumulate_minimal_n;
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/// Minimal input size for adjacent_difference.
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unsigned int adjacent_difference_minimal_n;
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/// Minimal input size for count and count_if.
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_SequenceIndex count_minimal_n;
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/// Minimal input size for fill.
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_SequenceIndex fill_minimal_n;
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/// Block size increase factor for find.
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double find_increasing_factor;
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/// Initial block size for find.
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_SequenceIndex find_initial_block_size;
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/// Maximal block size for find.
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_SequenceIndex find_maximum_block_size;
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/// Start with looking for this many elements sequentially, for find.
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_SequenceIndex find_sequential_search_size;
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/// Minimal input size for for_each.
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_SequenceIndex for_each_minimal_n;
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/// Minimal input size for generate.
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_SequenceIndex generate_minimal_n;
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/// Minimal input size for max_element.
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_SequenceIndex max_element_minimal_n;
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/// Minimal input size for merge.
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_SequenceIndex merge_minimal_n;
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/// Oversampling factor for merge.
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unsigned int merge_oversampling;
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/// Minimal input size for min_element.
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_SequenceIndex min_element_minimal_n;
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/// Minimal input size for multiway_merge.
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_SequenceIndex multiway_merge_minimal_n;
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/// Oversampling factor for multiway_merge.
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int multiway_merge_minimal_k;
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/// Oversampling factor for multiway_merge.
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unsigned int multiway_merge_oversampling;
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/// Minimal input size for nth_element.
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_SequenceIndex nth_element_minimal_n;
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/// Chunk size for partition.
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_SequenceIndex partition_chunk_size;
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/// Chunk size for partition, relative to input size. If > 0.0,
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/// this value overrides partition_chunk_size.
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double partition_chunk_share;
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/// Minimal input size for partition.
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_SequenceIndex partition_minimal_n;
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/// Minimal input size for partial_sort.
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_SequenceIndex partial_sort_minimal_n;
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/// Ratio for partial_sum. Assume "sum and write result" to be
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/// this factor slower than just "sum".
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float partial_sum_dilation;
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/// Minimal input size for partial_sum.
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unsigned int partial_sum_minimal_n;
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/// Minimal input size for random_shuffle.
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unsigned int random_shuffle_minimal_n;
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/// Minimal input size for replace and replace_if.
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_SequenceIndex replace_minimal_n;
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/// Minimal input size for set_difference.
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_SequenceIndex set_difference_minimal_n;
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/// Minimal input size for set_intersection.
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_SequenceIndex set_intersection_minimal_n;
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/// Minimal input size for set_symmetric_difference.
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_SequenceIndex set_symmetric_difference_minimal_n;
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/// Minimal input size for set_union.
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_SequenceIndex set_union_minimal_n;
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/// Minimal input size for parallel sorting.
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_SequenceIndex sort_minimal_n;
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/// Oversampling factor for parallel std::sort (MWMS).
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unsigned int sort_mwms_oversampling;
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/// Such many samples to take to find a good pivot (quicksort).
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unsigned int sort_qs_num_samples_preset;
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/// Maximal subsequence __length to switch to unbalanced __base case.
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/// Applies to std::sort with dynamically load-balanced quicksort.
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_SequenceIndex sort_qsb_base_case_maximal_n;
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/// Minimal input size for parallel std::transform.
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_SequenceIndex transform_minimal_n;
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/// Minimal input size for unique_copy.
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_SequenceIndex unique_copy_minimal_n;
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_SequenceIndex workstealing_chunk_size;
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// Hardware dependent tuning parameters.
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/// size of the L1 cache in bytes (underestimation).
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unsigned long long L1_cache_size;
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/// size of the L2 cache in bytes (underestimation).
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unsigned long long L2_cache_size;
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/// size of the Translation Lookaside Buffer (underestimation).
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unsigned int TLB_size;
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/// Overestimation of cache line size. Used to avoid false
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/// sharing, i.e. elements of different threads are at least this
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/// amount apart.
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unsigned int cache_line_size;
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// Statistics.
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/// The number of stolen ranges in load-balanced quicksort.
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_SequenceIndex qsb_steals;
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/// Minimal input size for search and search_n.
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_SequenceIndex search_minimal_n;
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/// Block size scale-down factor with respect to current position.
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float find_scale_factor;
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/// Get the global settings.
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_GLIBCXX_CONST static const _Settings&
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get() throw();
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/// Set the global settings.
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static void
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set(_Settings&) throw();
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explicit
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_Settings() :
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algorithm_strategy(heuristic),
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sort_algorithm(MWMS),
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partial_sum_algorithm(LINEAR),
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multiway_merge_algorithm(LOSER_TREE),
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find_algorithm(CONSTANT_SIZE_BLOCKS),
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sort_splitting(EXACT),
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merge_splitting(EXACT),
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multiway_merge_splitting(EXACT),
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accumulate_minimal_n(1000),
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adjacent_difference_minimal_n(1000),
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count_minimal_n(1000),
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fill_minimal_n(1000),
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find_increasing_factor(2.0),
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find_initial_block_size(256),
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find_maximum_block_size(8192),
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find_sequential_search_size(256),
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for_each_minimal_n(1000),
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generate_minimal_n(1000),
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max_element_minimal_n(1000),
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merge_minimal_n(1000),
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merge_oversampling(10),
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min_element_minimal_n(1000),
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multiway_merge_minimal_n(1000),
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multiway_merge_minimal_k(2), multiway_merge_oversampling(10),
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nth_element_minimal_n(1000),
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partition_chunk_size(1000),
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partition_chunk_share(0.0),
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partition_minimal_n(1000),
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partial_sort_minimal_n(1000),
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partial_sum_dilation(1.0f),
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partial_sum_minimal_n(1000),
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random_shuffle_minimal_n(1000),
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replace_minimal_n(1000),
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set_difference_minimal_n(1000),
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set_intersection_minimal_n(1000),
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set_symmetric_difference_minimal_n(1000),
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set_union_minimal_n(1000),
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sort_minimal_n(1000),
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sort_mwms_oversampling(10),
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sort_qs_num_samples_preset(100),
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sort_qsb_base_case_maximal_n(100),
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transform_minimal_n(1000),
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unique_copy_minimal_n(10000),
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workstealing_chunk_size(100),
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L1_cache_size(16 << 10),
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L2_cache_size(256 << 10),
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TLB_size(128),
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cache_line_size(64),
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qsb_steals(0),
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search_minimal_n(1000),
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find_scale_factor(0.01f)
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{ }
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};
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}
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#endif /* _GLIBCXX_PARALLEL_SETTINGS_H */
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