Parallelizer.h
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1 // This file is part of Eigen, a lightweight C++ template library
2 // for linear algebra.
3 //
4 // Copyright (C) 2010 Gael Guennebaud <gael.guennebaud@inria.fr>
5 //
6 // This Source Code Form is subject to the terms of the Mozilla
7 // Public License v. 2.0. If a copy of the MPL was not distributed
8 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
9 
10 #ifndef EIGEN_PARALLELIZER_H
11 #define EIGEN_PARALLELIZER_H
12 
13 #if EIGEN_HAS_CXX11_ATOMIC
14 #include <atomic>
15 #endif
16 
17 namespace Eigen {
18 
19 namespace internal {
20 
23 {
24  static int m_maxThreads = -1;
25  EIGEN_UNUSED_VARIABLE(m_maxThreads)
26 
27  if(action==SetAction)
28  {
30  m_maxThreads = *v;
31  }
32  else if(action==GetAction)
33  {
35  #ifdef EIGEN_HAS_OPENMP
36  if(m_maxThreads>0)
37  *v = m_maxThreads;
38  else
40  #else
41  *v = 1;
42  #endif
43  }
44  else
45  {
46  eigen_internal_assert(false);
47  }
48 }
49 
50 }
51 
53 inline void initParallel()
54 {
55  int nbt;
57  std::ptrdiff_t l1, l2, l3;
59 }
60 
63 inline int nbThreads()
64 {
65  int ret;
67  return ret;
68 }
69 
72 inline void setNbThreads(int v)
73 {
75 }
76 
77 namespace internal {
78 
79 template<typename Index> struct GemmParallelInfo
80 {
82 
83  // volatile is not enough on all architectures (see bug 1572)
84  // to guarantee that when thread A says to thread B that it is
85  // done with packing a block, then all writes have been really
86  // carried out... C++11 memory model+atomic guarantees this.
87 #if EIGEN_HAS_CXX11_ATOMIC
88  std::atomic<Index> sync;
89  std::atomic<int> users;
90 #else
91  Index volatile sync;
92  int volatile users;
93 #endif
94 
97 };
98 
99 template<bool Condition, typename Functor, typename Index>
100 void parallelize_gemm(const Functor& func, Index rows, Index cols, Index depth, bool transpose)
101 {
102  // TODO when EIGEN_USE_BLAS is defined,
103  // we should still enable OMP for other scalar types
104  // Without C++11, we have to disable GEMM's parallelization on
105  // non x86 architectures because there volatile is not enough for our purpose.
106  // See bug 1572.
107 #if (! defined(EIGEN_HAS_OPENMP)) || defined(EIGEN_USE_BLAS) || ((!EIGEN_HAS_CXX11_ATOMIC) && !(EIGEN_ARCH_i386_OR_x86_64))
108  // FIXME the transpose variable is only needed to properly split
109  // the matrix product when multithreading is enabled. This is a temporary
110  // fix to support row-major destination matrices. This whole
111  // parallelizer mechanism has to be redesigned anyway.
113  EIGEN_UNUSED_VARIABLE(transpose);
114  func(0,rows, 0,cols);
115 #else
116 
117  // Dynamically check whether we should enable or disable OpenMP.
118  // The conditions are:
119  // - the max number of threads we can create is greater than 1
120  // - we are not already in a parallel code
121  // - the sizes are large enough
122 
123  // compute the maximal number of threads from the size of the product:
124  // This first heuristic takes into account that the product kernel is fully optimized when working with nr columns at once.
125  Index size = transpose ? rows : cols;
126  Index pb_max_threads = std::max<Index>(1,size / Functor::Traits::nr);
127 
128  // compute the maximal number of threads from the total amount of work:
129  double work = static_cast<double>(rows) * static_cast<double>(cols) *
130  static_cast<double>(depth);
131  double kMinTaskSize = 50000; // FIXME improve this heuristic.
132  pb_max_threads = std::max<Index>(1, std::min<Index>(pb_max_threads, static_cast<Index>( work / kMinTaskSize ) ));
133 
134  // compute the number of threads we are going to use
135  Index threads = std::min<Index>(nbThreads(), pb_max_threads);
136 
137  // if multi-threading is explicitly disabled, not useful, or if we already are in a parallel session,
138  // then abort multi-threading
139  // FIXME omp_get_num_threads()>1 only works for openmp, what if the user does not use openmp?
140  if((!Condition) || (threads==1) || (omp_get_num_threads()>1))
141  return func(0,rows, 0,cols);
142 
144  func.initParallelSession(threads);
145 
146  if(transpose)
148 
150 
151  #pragma omp parallel num_threads(threads)
152  {
154  // Note that the actual number of threads might be lower than the number of request ones.
155  Index actual_threads = omp_get_num_threads();
156 
157  Index blockCols = (cols / actual_threads) & ~Index(0x3);
158  Index blockRows = (rows / actual_threads);
159  blockRows = (blockRows/Functor::Traits::mr)*Functor::Traits::mr;
160 
161  Index r0 = i*blockRows;
162  Index actualBlockRows = (i+1==actual_threads) ? rows-r0 : blockRows;
163 
164  Index c0 = i*blockCols;
165  Index actualBlockCols = (i+1==actual_threads) ? cols-c0 : blockCols;
166 
167  info[i].lhs_start = r0;
168  info[i].lhs_length = actualBlockRows;
169 
170  if(transpose) func(c0, actualBlockCols, 0, rows, info);
171  else func(0, rows, c0, actualBlockCols, info);
172  }
173 #endif
174 }
175 
176 } // end namespace internal
177 
178 } // end namespace Eigen
179 
180 #endif // EIGEN_PARALLELIZER_H
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autogenerated on Fri Nov 1 2024 03:33:54