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35 /*! \libinternal \file
37 * Declares OpenMP wrappers to avoid conditional compilation.
39 * This module defines wrappers for OpenMP API functions and enables compiling
40 * code without conditional compilation even when OpenMP is turned off in the
42 * Therefore, OpenMP API functions should always be used through these wrappers
43 * and omp.h should never be directly included. Instead, this header should be
44 * used whenever OpenMP API functions are needed.
47 * \ingroup module_utility
49 #ifndef GMX_UTILITY_OMP_H
50 #define GMX_UTILITY_OMP_H
56 #ifndef GMX_NATIVE_WINDOWS
57 /* Ugly hack because the openmp implementation below hacks into the SIMD
58 * settings to decide when to use _mm_pause(). This should eventually be
59 * changed into proper detection of the intrinsics uses, not SIMD.
61 #if (defined GMX_SIMD_X86_SSE2) || (defined GMX_SIMD_X86_SSE4_1) || \
62 (defined GMX_SIMD_X86_AVX_128_FMA) || (defined GMX_SIMD_X86_AVX_256) || \
63 (defined GMX_SIMD_X86_AVX2_256)
64 # include <xmmintrin.h>
70 #include "basedefinitions.h"
77 /*! \addtogroup module_utility
82 * Returns an integer equal to or greater than the number of threads
83 * that would be available if a parallel region without num_threads were
84 * defined at that point in the code.
86 * Acts as a wrapper for omp_get_max_threads().
88 int gmx_omp_get_max_threads(void);
91 * Returns the number of processors available when the function is called.
93 * Acts as a wrapper around omp_get_num_procs().
95 int gmx_omp_get_num_procs(void);
98 * Returns the thread number of the thread executing within its thread team.
100 * Acts as a wrapper for omp_get_thread_num().
102 int gmx_omp_get_thread_num(void);
105 * Sets the number of threads in subsequent parallel regions, unless overridden
106 * by a num_threads clause.
108 * Acts as a wrapper for omp_set_num_threads().
110 void gmx_omp_set_num_threads(int num_threads);
113 * Check for externally set thread affinity to avoid conflicts with \Gromacs
116 * \param[out] message Receives the message to be shown to the user.
117 * \returns `true` if we can set thread affinity ourselves.
119 * While GNU OpenMP does not set affinity by default, the Intel OpenMP library
120 * does. This conflicts with the internal affinity (especially thread-MPI)
121 * setting, results in incorrectly locked threads, and causes dreadful performance.
123 * The KMP_AFFINITY environment variable is used by Intel, GOMP_CPU_AFFINITY
124 * by the GNU compilers (Intel also honors it well). If any of the variables
125 * is set, we should honor it and disable the internal pinning.
126 * When using Intel OpenMP, we will disable affinity if the user did not set it
127 * manually through one of the aforementioned environment variables.
129 * Note that the Intel OpenMP affinity disabling will only take effect if this
130 * function is called before the OpenMP library gets initialized, which happens
131 * when the first call is made into a compilation unit that contains OpenMP
134 * If this function returns `false`, the caller is responsible to disable the
135 * pinning, show the message from \p *message to the user, and free the memory
136 * allocated for \p *message.
137 * If the return value is `true`, \p *message is NULL.
139 gmx_bool gmx_omp_check_thread_affinity(char **message);
142 * Pause for use in a spin-wait loop.
144 static gmx_inline void gmx_pause()
147 /* Ugly hack because the openmp implementation below hacks into the SIMD
148 * settings to decide when to use _mm_pause(). This should eventually be
149 * changed into proper detection of the intrinsics uses, not SIMD.
151 #if ((defined GMX_SIMD_X86_SSE2) || (defined GMX_SIMD_X86_SSE4_1) || \
152 (defined GMX_SIMD_X86_AVX_128_FMA) || (defined GMX_SIMD_X86_AVX_256) || \
153 (defined GMX_SIMD_X86_AVX2_256)) && !defined(__MINGW32__)
154 /* Replace with tbb::internal::atomic_backoff when/if we use TBB */
156 #elif defined __MIC__
159 /* No wait for unknown architecture */