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linux-stable/include/linux/cache.h
Alexander Lobakin 2cb13dec8c cache: add __cacheline_group_{begin, end}_aligned() (+ couple more) 
__cacheline_group_begin(), unfortunately, doesn't align the group
anyhow. If it is wanted, then you need to do something like

__cacheline_group_begin(grp) __aligned(ALIGN)

which isn't really convenient nor compact.
Add the _aligned() counterparts to align the groups automatically to
either the specified alignment (optional) or ``SMP_CACHE_BYTES``.
Note that the actual struct layout will then be (on x64 with 64-byte CL):

struct x {
	u32 y;				// offset 0, size 4, padding 56
	__cacheline_group_begin__grp;	// offset 64, size 0
	u32 z;				// offset 64, size 4, padding 4
	__cacheline_group_end__grp;	// offset 72, size 0
	__cacheline_group_pad__grp;	// offset 72, size 0, padding 56
	u32 w;				// offset 128
};

The end marker is aligned to long, so that you can assert the struct
size more strictly, but the offset of the next field in the structure
will be aligned to the group alignment, so that the next field won't
fall into the group it's not intended to.

Add __LARGEST_ALIGN definition and LARGEST_ALIGN() macro.
__LARGEST_ALIGN is the value to which the compilers align fields when
__aligned_largest is specified. Sometimes, it might be needed to get
this value outside of variable definitions. LARGEST_ALIGN() is macro
which just aligns a value to __LARGEST_ALIGN.
Also add SMP_CACHE_ALIGN(), similar to L1_CACHE_ALIGN(), but using
``SMP_CACHE_BYTES`` instead of ``L1_CACHE_BYTES`` as the former
also accounts L2, needed in some cases.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
2024-07-10 10:19:59 -07:00

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/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __LINUX_CACHE_H
#define __LINUX_CACHE_H
#include <uapi/linux/kernel.h>
#include <asm/cache.h>
#ifndef L1_CACHE_ALIGN
#define L1_CACHE_ALIGN(x) __ALIGN_KERNEL(x, L1_CACHE_BYTES)
#endif
#ifndef SMP_CACHE_BYTES
#define SMP_CACHE_BYTES L1_CACHE_BYTES
#endif
/**
* SMP_CACHE_ALIGN - align a value to the L2 cacheline size
* @x: value to align
*
* On some architectures, L2 ("SMP") CL size is bigger than L1, and sometimes,
* this needs to be accounted.
*
* Return: aligned value.
*/
#ifndef SMP_CACHE_ALIGN
#define SMP_CACHE_ALIGN(x) ALIGN(x, SMP_CACHE_BYTES)
#endif
/*
* ``__aligned_largest`` aligns a field to the value most optimal for the
* target architecture to perform memory operations. Get the actual value
* to be able to use it anywhere else.
*/
#ifndef __LARGEST_ALIGN
#define __LARGEST_ALIGN sizeof(struct { long x; } __aligned_largest)
#endif
#ifndef LARGEST_ALIGN
#define LARGEST_ALIGN(x) ALIGN(x, __LARGEST_ALIGN)
#endif
/*
* __read_mostly is used to keep rarely changing variables out of frequently
* updated cachelines. Its use should be reserved for data that is used
* frequently in hot paths. Performance traces can help decide when to use
* this. You want __read_mostly data to be tightly packed, so that in the
* best case multiple frequently read variables for a hot path will be next
* to each other in order to reduce the number of cachelines needed to
* execute a critical path. We should be mindful and selective of its use.
* ie: if you're going to use it please supply a *good* justification in your
* commit log
*/
#ifndef __read_mostly
#define __read_mostly
#endif
/*
* __ro_after_init is used to mark things that are read-only after init (i.e.
* after mark_rodata_ro() has been called). These are effectively read-only,
* but may get written to during init, so can't live in .rodata (via "const").
*/
#ifndef __ro_after_init
#define __ro_after_init __section(".data..ro_after_init")
#endif
#ifndef ____cacheline_aligned
#define ____cacheline_aligned __attribute__((__aligned__(SMP_CACHE_BYTES)))
#endif
#ifndef ____cacheline_aligned_in_smp
#ifdef CONFIG_SMP
#define ____cacheline_aligned_in_smp ____cacheline_aligned
#else
#define ____cacheline_aligned_in_smp
#endif /* CONFIG_SMP */
#endif
#ifndef __cacheline_aligned
#define __cacheline_aligned \
__attribute__((__aligned__(SMP_CACHE_BYTES), \
__section__(".data..cacheline_aligned")))
#endif /* __cacheline_aligned */
#ifndef __cacheline_aligned_in_smp
#ifdef CONFIG_SMP
#define __cacheline_aligned_in_smp __cacheline_aligned
#else
#define __cacheline_aligned_in_smp
#endif /* CONFIG_SMP */
#endif
/*
* The maximum alignment needed for some critical structures
* These could be inter-node cacheline sizes/L3 cacheline
* size etc. Define this in asm/cache.h for your arch
*/
#ifndef INTERNODE_CACHE_SHIFT
#define INTERNODE_CACHE_SHIFT L1_CACHE_SHIFT
#endif
#if !defined(____cacheline_internodealigned_in_smp)
#if defined(CONFIG_SMP)
#define ____cacheline_internodealigned_in_smp \
__attribute__((__aligned__(1 << (INTERNODE_CACHE_SHIFT))))
#else
#define ____cacheline_internodealigned_in_smp
#endif
#endif
#ifndef CONFIG_ARCH_HAS_CACHE_LINE_SIZE
#define cache_line_size() L1_CACHE_BYTES
#endif
#ifndef __cacheline_group_begin
#define __cacheline_group_begin(GROUP) \
__u8 __cacheline_group_begin__##GROUP[0]
#endif
#ifndef __cacheline_group_end
#define __cacheline_group_end(GROUP) \
__u8 __cacheline_group_end__##GROUP[0]
#endif
/**
* __cacheline_group_begin_aligned - declare an aligned group start
* @GROUP: name of the group
* @...: optional group alignment
*
* The following block inside a struct:
*
* __cacheline_group_begin_aligned(grp);
* field a;
* field b;
* __cacheline_group_end_aligned(grp);
*
* will always be aligned to either the specified alignment or
* ``SMP_CACHE_BYTES``.
*/
#define __cacheline_group_begin_aligned(GROUP, ...) \
__cacheline_group_begin(GROUP) \
__aligned((__VA_ARGS__ + 0) ? : SMP_CACHE_BYTES)
/**
* __cacheline_group_end_aligned - declare an aligned group end
* @GROUP: name of the group
* @...: optional alignment (same as was in __cacheline_group_begin_aligned())
*
* Note that the end marker is aligned to sizeof(long) to allow more precise
* size assertion. It also declares a padding at the end to avoid next field
* falling into this cacheline.
*/
#define __cacheline_group_end_aligned(GROUP, ...) \
__cacheline_group_end(GROUP) __aligned(sizeof(long)); \
struct { } __cacheline_group_pad__##GROUP \
__aligned((__VA_ARGS__ + 0) ? : SMP_CACHE_BYTES)
#ifndef CACHELINE_ASSERT_GROUP_MEMBER
#define CACHELINE_ASSERT_GROUP_MEMBER(TYPE, GROUP, MEMBER) \
BUILD_BUG_ON(!(offsetof(TYPE, MEMBER) >= \
offsetofend(TYPE, __cacheline_group_begin__##GROUP) && \
offsetofend(TYPE, MEMBER) <= \
offsetof(TYPE, __cacheline_group_end__##GROUP)))
#endif
#ifndef CACHELINE_ASSERT_GROUP_SIZE
#define CACHELINE_ASSERT_GROUP_SIZE(TYPE, GROUP, SIZE) \
BUILD_BUG_ON(offsetof(TYPE, __cacheline_group_end__##GROUP) - \
offsetofend(TYPE, __cacheline_group_begin__##GROUP) > \
SIZE)
#endif
/*
* Helper to add padding within a struct to ensure data fall into separate
* cachelines.
*/
#if defined(CONFIG_SMP)
struct cacheline_padding {
char x[0];
} ____cacheline_internodealigned_in_smp;
#define CACHELINE_PADDING(name) struct cacheline_padding name
#else
#define CACHELINE_PADDING(name)
#endif
#ifdef ARCH_DMA_MINALIGN
#define ARCH_HAS_DMA_MINALIGN
#else
#define ARCH_DMA_MINALIGN __alignof__(unsigned long long)
#endif
#endif /* __LINUX_CACHE_H */
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