Line data    Source code

       1             : /* +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
       2             :    Copyright (c) 2014-2023 The plumed team
       3             :    (see the PEOPLE file at the root of the distribution for a list of names)
       4             : 
       5             :    See http://www.plumed.org for more information.
       6             : 
       7             :    This file is part of plumed, version 2.
       8             : 
       9             :    plumed is free software: you can redistribute it and/or modify
      10             :    it under the terms of the GNU Lesser General Public License as published by
      11             :    the Free Software Foundation, either version 3 of the License, or
      12             :    (at your option) any later version.
      13             : 
      14             :    plumed is distributed in the hope that it will be useful,
      15             :    but WITHOUT ANY WARRANTY; without even the implied warranty of
      16             :    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      17             :    GNU Lesser General Public License for more details.
      18             : 
      19             :    You should have received a copy of the GNU Lesser General Public License
      20             :    along with plumed.  If not, see <http://www.gnu.org/licenses/>.
      21             : +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ */
      22             : #ifndef __PLUMED_tools_OpenMP_h
      23             : #define __PLUMED_tools_OpenMP_h
      24             : 
      25             : #include <vector>
      26             : 
      27             : namespace PLMD {
      28             : 
      29             : namespace OpenMP {
      30             : 
      31             : /// Set number of threads that can be used by openMP
      32             : void setNumThreads(const unsigned nt);
      33             : 
      34             : /// Get number of threads that can be used by openMP
      35             : unsigned getNumThreads();
      36             : 
      37             : /// Returns a unique thread identification number within the current team
      38             : unsigned getThreadNum();
      39             : 
      40             : /// get cacheline size
      41             : unsigned getCachelineSize();
      42             : 
      43             : /// Get a reasonable number of threads so as to access to an array of size s located at x
      44             : template<typename T>
      45      353527 : unsigned getGoodNumThreads(const T* /*getTheType*/,unsigned n) {
      46             :   // this is more or less the equivalent of writing "unsigned getGoodNumThreads<T>(unsigned n)"
      47             : 
      48             :   // a factor two is necessary since there is no guarantee that x is aligned
      49             :   // to cache line boundary
      50      353527 :   unsigned m=n*sizeof(T)/(2*getCachelineSize());
      51      353527 :   unsigned numThreads=getNumThreads();
      52      353527 :   if(m>=numThreads) {
      53             :     m=numThreads;
      54             :   } else {
      55             :     //it is better to use either all the active threads or only one
      56             :     //this solves a performance problem as explained in issue #415
      57             :     m=1;
      58             :   }
      59      353527 :   return m;
      60             : }
      61             : 
      62             : /// Get a reasonable number of threads so as to access to vector v
      63             : template<typename T>
      64        1350 : unsigned getGoodNumThreads(const std::vector<T> & v) {
      65        1350 :   if(v.size()==0) return 1;
      66        1314 :   else return getGoodNumThreads(&v[0],v.size());
      67             : }
      68             : 
      69             : }//namespace OpenMP
      70             : }//namespace PLMD
      71             : 
      72             : #endif