LXR linux/include/linux/percpu-defs.h

   1#ifndef _LINUX_PERCPU_DEFS_H
   2#define _LINUX_PERCPU_DEFS_H
   3
   4/*
   5 * Determine the real variable name from the name visible in the
   6 * kernel sources.
   7 */
   8#define per_cpu_var(var) per_cpu__##var
   9
  10/*
  11 * Base implementations of per-CPU variable declarations and definitions, where
  12 * the section in which the variable is to be placed is provided by the
  13 * 'sec' argument.  This may be used to affect the parameters governing the
  14 * variable's storage.
  15 *
  16 * NOTE!  The sections for the DECLARE and for the DEFINE must match, lest
  17 * linkage errors occur due the compiler generating the wrong code to access
  18 * that section.
  19 */
  20#define __PCPU_ATTRS(sec)                                               \
  21        __attribute__((section(PER_CPU_BASE_SECTION sec)))              \
  22        PER_CPU_ATTRIBUTES
  23
  24#define __PCPU_DUMMY_ATTRS                                              \
  25        __attribute__((section(".discard"), unused))
  26
  27/*
  28 * s390 and alpha modules require percpu variables to be defined as
  29 * weak to force the compiler to generate GOT based external
  30 * references for them.  This is necessary because percpu sections
  31 * will be located outside of the usually addressable area.
  32 *
  33 * This definition puts the following two extra restrictions when
  34 * defining percpu variables.
  35 *
  36 * 1. The symbol must be globally unique, even the static ones.
  37 * 2. Static percpu variables cannot be defined inside a function.
  38 *
  39 * Archs which need weak percpu definitions should define
  40 * ARCH_NEEDS_WEAK_PER_CPU in asm/percpu.h when necessary.
  41 *
  42 * To ensure that the generic code observes the above two
  43 * restrictions, if CONFIG_DEBUG_FORCE_WEAK_PER_CPU is set weak
  44 * definition is used for all cases.
  45 */
  46#if defined(ARCH_NEEDS_WEAK_PER_CPU) || defined(CONFIG_DEBUG_FORCE_WEAK_PER_CPU)
  47/*
  48 * __pcpu_scope_* dummy variable is used to enforce scope.  It
  49 * receives the static modifier when it's used in front of
  50 * DEFINE_PER_CPU() and will trigger build failure if
  51 * DECLARE_PER_CPU() is used for the same variable.
  52 *
  53 * __pcpu_unique_* dummy variable is used to enforce symbol uniqueness
  54 * such that hidden weak symbol collision, which will cause unrelated
  55 * variables to share the same address, can be detected during build.
  56 */
  57#define DECLARE_PER_CPU_SECTION(type, name, sec)                        \
  58        extern __PCPU_DUMMY_ATTRS char __pcpu_scope_##name;             \
  59        extern __PCPU_ATTRS(sec) __typeof__(type) per_cpu__##name
  60
  61#define DEFINE_PER_CPU_SECTION(type, name, sec)                         \
  62        __PCPU_DUMMY_ATTRS char __pcpu_scope_##name;                    \
  63        __PCPU_DUMMY_ATTRS char __pcpu_unique_##name;                   \
  64        __PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES __weak                 \
  65        __typeof__(type) per_cpu__##name
  66#else
  67/*
  68 * Normal declaration and definition macros.
  69 */
  70#define DECLARE_PER_CPU_SECTION(type, name, sec)                        \
  71        extern __PCPU_ATTRS(sec) __typeof__(type) per_cpu__##name
  72
  73#define DEFINE_PER_CPU_SECTION(type, name, sec)                         \
  74        __PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES                        \
  75        __typeof__(type) per_cpu__##name
  76#endif
  77
  78/*
  79 * Variant on the per-CPU variable declaration/definition theme used for
  80 * ordinary per-CPU variables.
  81 */
  82#define DECLARE_PER_CPU(type, name)                                     \
  83        DECLARE_PER_CPU_SECTION(type, name, "")
  84
  85#define DEFINE_PER_CPU(type, name)                                      \
  86        DEFINE_PER_CPU_SECTION(type, name, "")
  87
  88/*
  89 * Declaration/definition used for per-CPU variables that must come first in
  90 * the set of variables.
  91 */
  92#define DECLARE_PER_CPU_FIRST(type, name)                               \
  93        DECLARE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
  94
  95#define DEFINE_PER_CPU_FIRST(type, name)                                \
  96        DEFINE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
  97
  98/*
  99 * Declaration/definition used for per-CPU variables that must be cacheline
 100 * aligned under SMP conditions so that, whilst a particular instance of the
 101 * data corresponds to a particular CPU, inefficiencies due to direct access by
 102 * other CPUs are reduced by preventing the data from unnecessarily spanning
 103 * cachelines.
 104 *
 105 * An example of this would be statistical data, where each CPU's set of data
 106 * is updated by that CPU alone, but the data from across all CPUs is collated
 107 * by a CPU processing a read from a proc file.
 108 */
 109#define DECLARE_PER_CPU_SHARED_ALIGNED(type, name)                      \
 110        DECLARE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
 111        ____cacheline_aligned_in_smp
 112
 113#define DEFINE_PER_CPU_SHARED_ALIGNED(type, name)                       \
 114        DEFINE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
 115        ____cacheline_aligned_in_smp
 116
 117#define DECLARE_PER_CPU_ALIGNED(type, name)                             \
 118        DECLARE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)    \
 119        ____cacheline_aligned
 120
 121#define DEFINE_PER_CPU_ALIGNED(type, name)                              \
 122        DEFINE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)     \
 123        ____cacheline_aligned
 124
 125/*
 126 * Declaration/definition used for per-CPU variables that must be page aligned.
 127 */
 128#define DECLARE_PER_CPU_PAGE_ALIGNED(type, name)                        \
 129        DECLARE_PER_CPU_SECTION(type, name, ".page_aligned")            \
 130        __aligned(PAGE_SIZE)
 131
 132#define DEFINE_PER_CPU_PAGE_ALIGNED(type, name)                         \
 133        DEFINE_PER_CPU_SECTION(type, name, ".page_aligned")             \
 134        __aligned(PAGE_SIZE)
 135
 136/*
 137 * Intermodule exports for per-CPU variables.
 138 */
 139#define EXPORT_PER_CPU_SYMBOL(var) EXPORT_SYMBOL(per_cpu__##var)
 140#define EXPORT_PER_CPU_SYMBOL_GPL(var) EXPORT_SYMBOL_GPL(per_cpu__##var)
 141
 142
 143#endif /* _LINUX_PERCPU_DEFS_H */
 144