include/linux/percpu-defs.h

   1 #ifndef _LINUX_PERCPU_DEFS_H
   2 #define _LINUX_PERCPU_DEFS_H
   3
   4 /*
   5  * Base implementations of per-CPU variable declarations and definitions, where
   6  * the section in which the variable is to be placed is provided by the
   7  * 'sec' argument.  This may be used to affect the parameters governing the
   8  * variable's storage.
   9  *
  10  * NOTE!  The sections for the DECLARE and for the DEFINE must match, lest
  11  * linkage errors occur due the compiler generating the wrong code to access
  12  * that section.
  13  */
  14 #define __PCPU_ATTRS(sec)                                               \
  15         __percpu __attribute__((section(PER_CPU_BASE_SECTION sec)))     \
  16         PER_CPU_ATTRIBUTES
  17
  18 #define __PCPU_DUMMY_ATTRS                                              \
  19         __attribute__((section(".discard"), unused))
  20
  21 /*
  22  * s390 and alpha modules require percpu variables to be defined as
  23  * weak to force the compiler to generate GOT based external
  24  * references for them.  This is necessary because percpu sections
  25  * will be located outside of the usually addressable area.
  26  *
  27  * This definition puts the following two extra restrictions when
  28  * defining percpu variables.
  29  *
  30  * 1. The symbol must be globally unique, even the static ones.
  31  * 2. Static percpu variables cannot be defined inside a function.
  32  *
  33  * Archs which need weak percpu definitions should define
  34  * ARCH_NEEDS_WEAK_PER_CPU in asm/percpu.h when necessary.
  35  *
  36  * To ensure that the generic code observes the above two
  37  * restrictions, if CONFIG_DEBUG_FORCE_WEAK_PER_CPU is set weak
  38  * definition is used for all cases.
  39  */
  40 #if defined(ARCH_NEEDS_WEAK_PER_CPU) || defined(CONFIG_DEBUG_FORCE_WEAK_PER_CPU)
  41 /*
  42  * __pcpu_scope_* dummy variable is used to enforce scope.  It
  43  * receives the static modifier when it's used in front of
  44  * DEFINE_PER_CPU() and will trigger build failure if
  45  * DECLARE_PER_CPU() is used for the same variable.
  46  *
  47  * __pcpu_unique_* dummy variable is used to enforce symbol uniqueness
  48  * such that hidden weak symbol collision, which will cause unrelated
  49  * variables to share the same address, can be detected during build.
  50  */
  51 #define DECLARE_PER_CPU_SECTION(type, name, sec)                        \
  52         extern __PCPU_DUMMY_ATTRS char __pcpu_scope_##name;             \
  53         extern __PCPU_ATTRS(sec) __typeof__(type) name
  54
  55 #define DEFINE_PER_CPU_SECTION(type, name, sec)                         \
  56         __PCPU_DUMMY_ATTRS char __pcpu_scope_##name;                    \
  57         extern __PCPU_DUMMY_ATTRS char __pcpu_unique_##name;            \
  58         __PCPU_DUMMY_ATTRS char __pcpu_unique_##name;                   \
  59         __PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES __weak                 \
  60         __typeof__(type) name
  61 #else
  62 /*
  63  * Normal declaration and definition macros.
  64  */
  65 #define DECLARE_PER_CPU_SECTION(type, name, sec)                        \
  66         extern __PCPU_ATTRS(sec) __typeof__(type) name
  67
  68 #define DEFINE_PER_CPU_SECTION(type, name, sec)                         \
  69         __PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES                        \
  70         __typeof__(type) name
  71 #endif
  72
  73 /*
  74  * Variant on the per-CPU variable declaration/definition theme used for
  75  * ordinary per-CPU variables.
  76  */
  77 #define DECLARE_PER_CPU(type, name)                                     \
  78         DECLARE_PER_CPU_SECTION(type, name, "")
  79
  80 #define DEFINE_PER_CPU(type, name)                                      \
  81         DEFINE_PER_CPU_SECTION(type, name, "")
  82
  83 /*
  84  * Declaration/definition used for per-CPU variables that must come first in
  85  * the set of variables.
  86  */
  87 #define DECLARE_PER_CPU_FIRST(type, name)                               \
  88         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
  89
  90 #define DEFINE_PER_CPU_FIRST(type, name)                                \
  91         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
  92
  93 /*
  94  * Declaration/definition used for per-CPU variables that must be cacheline
  95  * aligned under SMP conditions so that, whilst a particular instance of the
  96  * data corresponds to a particular CPU, inefficiencies due to direct access by
  97  * other CPUs are reduced by preventing the data from unnecessarily spanning
  98  * cachelines.
  99  *
 100  * An example of this would be statistical data, where each CPU's set of data
 101  * is updated by that CPU alone, but the data from across all CPUs is collated
 102  * by a CPU processing a read from a proc file.
 103  */
 104 #define DECLARE_PER_CPU_SHARED_ALIGNED(type, name)                      \
 105         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
 106         ____cacheline_aligned_in_smp
 107
 108 #define DEFINE_PER_CPU_SHARED_ALIGNED(type, name)                       \
 109         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
 110         ____cacheline_aligned_in_smp
 111
 112 #define DECLARE_PER_CPU_ALIGNED(type, name)                             \
 113         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)    \
 114         ____cacheline_aligned
 115
 116 #define DEFINE_PER_CPU_ALIGNED(type, name)                              \
 117         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)     \
 118         ____cacheline_aligned
 119
 120 /*
 121  * Declaration/definition used for per-CPU variables that must be page aligned.
 122  */
 123 #define DECLARE_PER_CPU_PAGE_ALIGNED(type, name)                        \
 124         DECLARE_PER_CPU_SECTION(type, name, ".page_aligned")            \
 125         __aligned(PAGE_SIZE)
 126
 127 #define DEFINE_PER_CPU_PAGE_ALIGNED(type, name)                         \
 128         DEFINE_PER_CPU_SECTION(type, name, ".page_aligned")             \
 129         __aligned(PAGE_SIZE)
 130
 131 /*
 132  * Intermodule exports for per-CPU variables.
 133  */
 134 #define EXPORT_PER_CPU_SYMBOL(var) EXPORT_SYMBOL(var)
 135 #define EXPORT_PER_CPU_SYMBOL_GPL(var) EXPORT_SYMBOL_GPL(var)
 136
 137
 138 #endif /* _LINUX_PERCPU_DEFS_H */