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 */