mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-09-04 09:59:32 +00:00
![Luis Chamberlain](/assets/img/avatar_default.png)
__read_mostly can easily be misused by folks, its not meant for just read-only data. There are performance reasons for using it, but we also don't provide any guidance about its use. Provide a bit more guidance over its use. Signed-off-by: Luis Chamberlain <mcgrof@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Kees Cook <keescook@chromium.org> Acked-by: Christoph Lameter <cl@linux.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Matthew Wilcox <willy@infradead.org> Link: http://lkml.kernel.org/r/20200507161424.2584-1-mcgrof@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
88 lines
2.6 KiB
C
88 lines
2.6 KiB
C
/* 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
|
|
|
|
/*
|
|
* __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 __attribute__((__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
|
|
|
|
#endif /* __LINUX_CACHE_H */
|