LXR linux/include/linux/cache.h

   1/* SPDX-License-Identifier: GPL-2.0 */
   2#ifndef __LINUX_CACHE_H
   3#define __LINUX_CACHE_H
   4
   5#include <uapi/linux/kernel.h>
   6#include <asm/cache.h>
   7
   8#ifndef L1_CACHE_ALIGN
   9#define L1_CACHE_ALIGN(x) __ALIGN_KERNEL(x, L1_CACHE_BYTES)
  10#endif
  11
  12#ifndef SMP_CACHE_BYTES
  13#define SMP_CACHE_BYTES L1_CACHE_BYTES
  14#endif
  15
  16/*
  17 * __read_mostly is used to keep rarely changing variables out of frequently
  18 * updated cachelines. Its use should be reserved for data that is used
  19 * frequently in hot paths. Performance traces can help decide when to use
  20 * this. You want __read_mostly data to be tightly packed, so that in the
  21 * best case multiple frequently read variables for a hot path will be next
  22 * to each other in order to reduce the number of cachelines needed to
  23 * execute a critical path. We should be mindful and selective of its use.
  24 * ie: if you're going to use it please supply a *good* justification in your
  25 * commit log
  26 */
  27#ifndef __read_mostly
  28#define __read_mostly
  29#endif
  30
  31/*
  32 * __ro_after_init is used to mark things that are read-only after init (i.e.
  33 * after mark_rodata_ro() has been called). These are effectively read-only,
  34 * but may get written to during init, so can't live in .rodata (via "const").
  35 */
  36#ifndef __ro_after_init
  37#define __ro_after_init __section(".data..ro_after_init")
  38#endif
  39
  40#ifndef ____cacheline_aligned
  41#define ____cacheline_aligned __attribute__((__aligned__(SMP_CACHE_BYTES)))
  42#endif
  43
  44#ifndef ____cacheline_aligned_in_smp
  45#ifdef CONFIG_SMP
  46#define ____cacheline_aligned_in_smp ____cacheline_aligned
  47#else
  48#define ____cacheline_aligned_in_smp
  49#endif /* CONFIG_SMP */
  50#endif
  51
  52#ifndef __cacheline_aligned
  53#define __cacheline_aligned                                     \
  54  __attribute__((__aligned__(SMP_CACHE_BYTES),                  \
  55                 __section__(".data..cacheline_aligned")))
  56#endif /* __cacheline_aligned */
  57
  58#ifndef __cacheline_aligned_in_smp
  59#ifdef CONFIG_SMP
  60#define __cacheline_aligned_in_smp __cacheline_aligned
  61#else
  62#define __cacheline_aligned_in_smp
  63#endif /* CONFIG_SMP */
  64#endif
  65
  66/*
  67 * The maximum alignment needed for some critical structures
  68 * These could be inter-node cacheline sizes/L3 cacheline
  69 * size etc.  Define this in asm/cache.h for your arch
  70 */
  71#ifndef INTERNODE_CACHE_SHIFT
  72#define INTERNODE_CACHE_SHIFT L1_CACHE_SHIFT
  73#endif
  74
  75#if !defined(____cacheline_internodealigned_in_smp)
  76#if defined(CONFIG_SMP)
  77#define ____cacheline_internodealigned_in_smp \
  78        __attribute__((__aligned__(1 << (INTERNODE_CACHE_SHIFT))))
  79#else
  80#define ____cacheline_internodealigned_in_smp
  81#endif
  82#endif
  83
  84#ifndef CONFIG_ARCH_HAS_CACHE_LINE_SIZE
  85#define cache_line_size()       L1_CACHE_BYTES
  86#endif
  87
  88#endif /* __LINUX_CACHE_H */
  89