src/gromacs/utility/alignedallocator.h

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  35 /*! \file
  36  * \brief Declares allocation policy classes and allocators that are
  37  * used to make library containers compatible with alignment
  38  * requirements of particular hardware, e.g. memory operations for
  39  * SIMD or accelerators.
  40  *
  41  * \author Erik Lindahl <erik.lindahl@gmail.com>
  42  * \author Mark Abraham <mark.j.abraham@gmail.com>
  43  * \inpublicapi
  44  * \ingroup module_utility
  45  */
  46 #ifndef GMX_UTILITY_ALIGNEDALLOCATOR_H
  47 #define GMX_UTILITY_ALIGNEDALLOCATOR_H
  48
  49 #include <cstddef>
  50
  51 #include "gromacs/utility/allocator.h"
  52
  53 namespace gmx
  54 {
  55
  56 /*! \libinternal \brief Policy class for configuring gmx::Allocator, to manage
  57  * allocations of aligned memory for SIMD code.
  58  */
  59 class AlignedAllocationPolicy
  60 {
  61     public:
  62         /*! \brief Return the alignment size. */
  63         static std::size_t
  64         alignment();
  65         /*! \brief Allocate memory aligned to alignment() bytes.
  66          *
  67          *  \param bytes Amount of memory (bytes) to allocate. It is valid to ask for
  68          *               0 bytes, which will return a non-null pointer that is properly
  69          *               aligned and padded (but that you should not use).
  70          *
  71          * \return Valid pointer if the allocation worked, otherwise nullptr.
  72          *
  73          * The memory will always be aligned to 128 bytes, which is our
  74          * estimate of the longest cache lines on architectures currently in use.
  75          * It will also be padded by the same amount at the end of the
  76          * area, to help avoid false cache sharing.
  77          *
  78          *  \note Memory allocated with this routine must be released with
  79          *        gmx::AlignedAllocationPolicy::free(), and absolutely not the system free().
  80          */
  81         static void *
  82         malloc(std::size_t bytes);
  83         /*! \brief Free aligned memory
  84          *
  85          *  \param p  Memory pointer previously returned from malloc()
  86          *
  87          *  \note This routine should only be called with pointers obtained from
  88          *        gmx::AlignedAllocationPolicy::malloc(), and absolutely not any
  89          *        pointers obtained the system malloc().
  90          */
  91         static void
  92         free(void *p);
  93 };
  94
  95 /*! \brief Aligned memory allocator.
  96  *
  97  *  \tparam T          Type of objects to allocate
  98  *
  99  * This convenience partial specialization can be used for the
 100  * optional allocator template parameter in standard library
 101  * containers, which is necessary e.g. to use SIMD aligned load and
 102  * store operations on data in those containers. The memory will
 103  * always be aligned according to the behavior of
 104  * AlignedAllocationPolicy.
 105  */
 106 template <class T>
 107 using AlignedAllocator = Allocator<T, AlignedAllocationPolicy>;
 108
 109
 110 /*! \brief Return the memory page size on this system
 111  *
 112  * Implements the "construct on first use" idiom to avoid the static
 113  * initialization order fiasco where a possible static page-aligned
 114  * container would be initialized before the alignment variable was.
 115  *
 116  * Note that thread-safety is guaranteed by the C++11 language
 117  * standard. */
 118 std::size_t pageSize();
 119
 120 /*! \libinternal \brief Policy class for configuring gmx::Allocator,
 121  * to manage allocations of page-aligned memory that can be locked for
 122  * asynchronous transfer to GPU devices.
 123  */
 124 class PageAlignedAllocationPolicy
 125 {
 126     public:
 127         /*! \brief Return the alignment size of memory pages on this system.
 128          *
 129          * Queries sysconf/WinAPI, otherwise guesses 4096. */
 130         static std::size_t
 131         alignment();
 132         /*! \brief Allocate memory aligned to alignment() bytes.
 133          *
 134          *  \param bytes Amount of memory (bytes) to allocate. It is valid to ask for
 135          *               0 bytes, which will return a non-null pointer that is properly
 136          *               aligned and padded (but that you should not use).
 137          *
 138          * \return Valid pointer if the allocation worked, otherwise nullptr.
 139          *
 140          *  \note Memory allocated with this routine must be released with
 141          *        gmx::PageAlignedAllocationPolicy::free(), and absolutely not the system free().
 142          */
 143         static void *
 144         malloc(std::size_t bytes);
 145         /*! \brief Free aligned memory
 146          *
 147          *  \param p  Memory pointer previously returned from malloc()
 148          *
 149          *  \note This routine should only be called with pointers obtained from
 150          *        gmx::PageAlignedAllocationPolicy::malloc(), and absolutely not any
 151          *        pointers obtained the system malloc().
 152          */
 153         static void
 154         free(void *p);
 155 };
 156
 157 /*! \brief PageAligned memory allocator.
 158  *
 159  *  \tparam T          Type of objects to allocate
 160  *
 161  * This convenience partial specialization can be used for the
 162  * optional allocator template parameter in standard library
 163  * containers, which is necessary for locking memory pages for
 164  * asynchronous transfer between a GPU device and the host.  The
 165  * memory will always be aligned according to the behavior of
 166  * PageAlignedAllocationPolicy.
 167  */
 168 template <class T>
 169 using PageAlignedAllocator = Allocator<T, PageAlignedAllocationPolicy>;
 170
 171 }      // namespace gmx
 172
 173 #endif // GMX_UTILITY_ALIGNEDALLOCATOR_H