libstdc++

settings.h
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1 // -*- C++ -*-
2
3 // Copyright (C) 2007-2013 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the terms
7 // of the GNU General Public License as published by the Free Software
8 // Foundation; either version 3, or (at your option) any later
9 // version.
10
11 // This library is distributed in the hope that it will be useful, but
12 // WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 // General Public License for more details.
15
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24
25 /** @file parallel/settings.h
26 * @brief Runtime settings and tuning parameters, heuristics to decide
27 * whether to use parallelized algorithms.
28 * This file is a GNU parallel extension to the Standard C++ Library.
29 *
30 * @section parallelization_decision
31 * The decision whether to run an algorithm in parallel.
32 *
33 * There are several ways the user can switch on and __off the parallel
34 * execution of an algorithm, both at compile- and run-time.
35 *
36 * Only sequential execution can be forced at compile-time. This
37 * reduces code size and protects code parts that have
38 * non-thread-safe side effects.
39 *
40 * Ultimately, forcing parallel execution at compile-time makes
41 * sense. Often, the sequential algorithm implementation is used as
42 * a subroutine, so no reduction in code size can be achieved. Also,
43 * the machine the program is run on might have only one processor
44 * core, so to avoid overhead, the algorithm is executed
45 * sequentially.
46 *
47 * To force sequential execution of an algorithm ultimately at
48 * compile-time, the user must add the tag
49 * gnu_parallel::sequential_tag() to the end of the parameter list,
50 * e. g.
51 *
52 * \code
53 * std::sort(__v.begin(), __v.end(), __gnu_parallel::sequential_tag());
54 * \endcode
55 *
56 * This is compatible with all overloaded algorithm variants. No
57 * additional code will be instantiated, at all. The same holds for
58 * most algorithm calls with iterators not providing random access.
59 *
60 * If the algorithm call is not forced to be executed sequentially
61 * at compile-time, the decision is made at run-time.
62 * The global variable __gnu_parallel::_Settings::algorithm_strategy
63 * is checked. _It is a tristate variable corresponding to:
64 *
65 * a. force_sequential, meaning the sequential algorithm is executed.
66 * b. force_parallel, meaning the parallel algorithm is executed.
67 * c. heuristic
68 *
69 * For heuristic, the parallel algorithm implementation is called
70 * only if the input size is sufficiently large. For most
71 * algorithms, the input size is the (combined) length of the input
72 * sequence(__s). The threshold can be set by the user, individually
73 * for each algorithm. The according variables are called
74 * gnu_parallel::_Settings::[algorithm]_minimal_n .
75 *
76 * For some of the algorithms, there are even more tuning options,
77 * e. g. the ability to choose from multiple algorithm variants. See
78 * below for details.
79 */
80
81 // Written by Johannes Singler and Felix Putze.
82
83 #ifndef _GLIBCXX_PARALLEL_SETTINGS_H
84 #define _GLIBCXX_PARALLEL_SETTINGS_H 1
85
86 #include <parallel/types.h>
87
88 /**
89 * @brief Determine at compile(?)-time if the parallel variant of an
90 * algorithm should be called.
91 * @param __c A condition that is convertible to bool that is overruled by
92 * __gnu_parallel::_Settings::algorithm_strategy. Usually a decision
93 * based on the input size.
94 */
95 #define _GLIBCXX_PARALLEL_CONDITION(__c) \
96 (__gnu_parallel::_Settings::get().algorithm_strategy \
97 != __gnu_parallel::force_sequential \
98 && ((__gnu_parallel::__get_max_threads() > 1 && (__c)) \
99 || __gnu_parallel::_Settings::get().algorithm_strategy \
100 == __gnu_parallel::force_parallel))
101
102 /*
103 inline bool
104 parallel_condition(bool __c)
105 {
106 bool ret = false;
107 const _Settings& __s = _Settings::get();
108 if (__s.algorithm_strategy != force_seqential)
109 {
110 if (__s.algorithm_strategy == force_parallel)
111 ret = true;
112 else
113 ret = __get_max_threads() > 1 && __c;
114 }
115 return ret;
116 }
117 */
118
119 namespace __gnu_parallel
120 {
121 /// class _Settings
122 /// Run-time settings for the parallel mode including all tunable parameters.
123 struct _Settings
124 {
125 _AlgorithmStrategy algorithm_strategy;
126
127 _SortAlgorithm sort_algorithm;
128 _PartialSumAlgorithm partial_sum_algorithm;
129 _MultiwayMergeAlgorithm multiway_merge_algorithm;
130 _FindAlgorithm find_algorithm;
131
132 _SplittingAlgorithm sort_splitting;
133 _SplittingAlgorithm merge_splitting;
134 _SplittingAlgorithm multiway_merge_splitting;
135
136 // Per-algorithm settings.
137
138 /// Minimal input size for accumulate.
139 _SequenceIndex accumulate_minimal_n;
140
141 /// Minimal input size for adjacent_difference.
142 unsigned int adjacent_difference_minimal_n;
143
144 /// Minimal input size for count and count_if.
145 _SequenceIndex count_minimal_n;
146
147 /// Minimal input size for fill.
148 _SequenceIndex fill_minimal_n;
149
150 /// Block size increase factor for find.
151 double find_increasing_factor;
152
153 /// Initial block size for find.
154 _SequenceIndex find_initial_block_size;
155
156 /// Maximal block size for find.
157 _SequenceIndex find_maximum_block_size;
158
159 /// Start with looking for this many elements sequentially, for find.
160 _SequenceIndex find_sequential_search_size;
161
162 /// Minimal input size for for_each.
163 _SequenceIndex for_each_minimal_n;
164
165 /// Minimal input size for generate.
166 _SequenceIndex generate_minimal_n;
167
168 /// Minimal input size for max_element.
169 _SequenceIndex max_element_minimal_n;
170
171 /// Minimal input size for merge.
172 _SequenceIndex merge_minimal_n;
173
174 /// Oversampling factor for merge.
175 unsigned int merge_oversampling;
176
177 /// Minimal input size for min_element.
178 _SequenceIndex min_element_minimal_n;
179
180 /// Minimal input size for multiway_merge.
181 _SequenceIndex multiway_merge_minimal_n;
182
183 /// Oversampling factor for multiway_merge.
184 int multiway_merge_minimal_k;
185
186 /// Oversampling factor for multiway_merge.
187 unsigned int multiway_merge_oversampling;
188
189 /// Minimal input size for nth_element.
190 _SequenceIndex nth_element_minimal_n;
191
192 /// Chunk size for partition.
193 _SequenceIndex partition_chunk_size;
194
195 /// Chunk size for partition, relative to input size. If > 0.0,
196 /// this value overrides partition_chunk_size.
197 double partition_chunk_share;
198
199 /// Minimal input size for partition.
200 _SequenceIndex partition_minimal_n;
201
202 /// Minimal input size for partial_sort.
203 _SequenceIndex partial_sort_minimal_n;
204
205 /// Ratio for partial_sum. Assume "sum and write result" to be
206 /// this factor slower than just "sum".
207 float partial_sum_dilation;
208
209 /// Minimal input size for partial_sum.
210 unsigned int partial_sum_minimal_n;
211
212 /// Minimal input size for random_shuffle.
213 unsigned int random_shuffle_minimal_n;
214
215 /// Minimal input size for replace and replace_if.
216 _SequenceIndex replace_minimal_n;
217
218 /// Minimal input size for set_difference.
219 _SequenceIndex set_difference_minimal_n;
220
221 /// Minimal input size for set_intersection.
222 _SequenceIndex set_intersection_minimal_n;
223
224 /// Minimal input size for set_symmetric_difference.
225 _SequenceIndex set_symmetric_difference_minimal_n;
226
227 /// Minimal input size for set_union.
228 _SequenceIndex set_union_minimal_n;
229
230 /// Minimal input size for parallel sorting.
231 _SequenceIndex sort_minimal_n;
232
233 /// Oversampling factor for parallel std::sort (MWMS).
234 unsigned int sort_mwms_oversampling;
235
236 /// Such many samples to take to find a good pivot (quicksort).
237 unsigned int sort_qs_num_samples_preset;
238
239 /// Maximal subsequence __length to switch to unbalanced __base case.
240 /// Applies to std::sort with dynamically load-balanced quicksort.
241 _SequenceIndex sort_qsb_base_case_maximal_n;
242
243 /// Minimal input size for parallel std::transform.
244 _SequenceIndex transform_minimal_n;
245
246 /// Minimal input size for unique_copy.
247 _SequenceIndex unique_copy_minimal_n;
248
249 _SequenceIndex workstealing_chunk_size;
250
251 // Hardware dependent tuning parameters.
252
253 /// size of the L1 cache in bytes (underestimation).
254 unsigned long long L1_cache_size;
255
256 /// size of the L2 cache in bytes (underestimation).
257 unsigned long long L2_cache_size;
258
259 /// size of the Translation Lookaside Buffer (underestimation).
260 unsigned int TLB_size;
261
262 /// Overestimation of cache line size. Used to avoid false
263 /// sharing, i.e. elements of different threads are at least this
264 /// amount apart.
265 unsigned int cache_line_size;
266
267 // Statistics.
268
269 /// The number of stolen ranges in load-balanced quicksort.
270 _SequenceIndex qsb_steals;
271
272 /// Minimal input size for search and search_n.
273 _SequenceIndex search_minimal_n;
274
275 /// Block size scale-down factor with respect to current position.
276 float find_scale_factor;
277
278 /// Get the global settings.
279 _GLIBCXX_CONST static const _Settings&
280 get() throw();
281
282 /// Set the global settings.
283 static void
284 set(_Settings&) throw();
285
286 explicit
287 _Settings() :
288 algorithm_strategy(heuristic),
289 sort_algorithm(MWMS),
290 partial_sum_algorithm(LINEAR),
291 multiway_merge_algorithm(LOSER_TREE),
292 find_algorithm(CONSTANT_SIZE_BLOCKS),
293 sort_splitting(EXACT),
294 merge_splitting(EXACT),
295 multiway_merge_splitting(EXACT),
296 accumulate_minimal_n(1000),
297 adjacent_difference_minimal_n(1000),
298 count_minimal_n(1000),
299 fill_minimal_n(1000),
300 find_increasing_factor(2.0),
301 find_initial_block_size(256),
302 find_maximum_block_size(8192),
303 find_sequential_search_size(256),
304 for_each_minimal_n(1000),
305 generate_minimal_n(1000),
306 max_element_minimal_n(1000),
307 merge_minimal_n(1000),
308 merge_oversampling(10),
309 min_element_minimal_n(1000),
310 multiway_merge_minimal_n(1000),
311 multiway_merge_minimal_k(2), multiway_merge_oversampling(10),
312 nth_element_minimal_n(1000),
313 partition_chunk_size(1000),
314 partition_chunk_share(0.0),
315 partition_minimal_n(1000),
316 partial_sort_minimal_n(1000),
317 partial_sum_dilation(1.0f),
318 partial_sum_minimal_n(1000),
319 random_shuffle_minimal_n(1000),
320 replace_minimal_n(1000),
321 set_difference_minimal_n(1000),
322 set_intersection_minimal_n(1000),
323 set_symmetric_difference_minimal_n(1000),
324 set_union_minimal_n(1000),
325 sort_minimal_n(1000),
326 sort_mwms_oversampling(10),
327 sort_qs_num_samples_preset(100),
328 sort_qsb_base_case_maximal_n(100),
329 transform_minimal_n(1000),
330 unique_copy_minimal_n(10000),
331 workstealing_chunk_size(100),
332 L1_cache_size(16 << 10),
333 L2_cache_size(256 << 10),
334 TLB_size(128),
335 cache_line_size(64),
336 qsb_steals(0),
337 search_minimal_n(1000),
338 find_scale_factor(0.01f)
339 { }
340 };
341 }
342
343 #endif /* _GLIBCXX_PARALLEL_SETTINGS_H */