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farmakis
51 lines
1.8 KiB
C++
51 lines
1.8 KiB
C++
/*========================== omp_num_threads.hpp ============================
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* include openmp and provide a function to compute a smart number of threads
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*
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* Hugo Raguet 2018
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*===========================================================================*/
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#pragma once
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#ifdef _OPENMP
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#include <omp.h>
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#include <cstdint> // requires C++11, needed for uintmax_t
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/* rough minimum number of operations per thread */
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#ifndef MIN_OPS_PER_THREAD
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#define MIN_OPS_PER_THREAD 10000
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#endif
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/* num_ops is a rough estimation of the total number of operations
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* max_threads is the maximum number of jobs performed in parallel */
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static inline int compute_num_threads(uintmax_t num_ops,
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uintmax_t max_threads)
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{
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uintmax_t num_threads = num_ops/MIN_OPS_PER_THREAD;
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if (num_threads > (unsigned) omp_get_max_threads()){
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num_threads = omp_get_max_threads();
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}
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if (num_threads > (unsigned) omp_get_num_procs()){
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num_threads = omp_get_num_procs();
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}
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if (num_threads > max_threads){ num_threads = max_threads; }
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return num_threads > 1 ? num_threads : 1;
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}
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/* overload for max_threads defaulting to num_ops */
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static inline int compute_num_threads(uintmax_t num_ops)
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{ return compute_num_threads(num_ops, num_ops); }
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#define NUM_THREADS(...) \
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num_threads(compute_num_threads((uintmax_t) __VA_ARGS__))
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#else /* provide default definitions for basic openmp queries */
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static inline int omp_get_num_procs(){ return 1; }
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static inline int omp_get_thread_num(){ return 0; }
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static inline int omp_get_max_threads(){ return 1; }
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static inline void omp_set_num_threads(int){ /* do nothing */ }
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static inline int compute_num_threads(int num_ops, int max_threads = 1)
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{ return 1; }
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#endif
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