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5028eaa97d
Collect the DECLARE/DEFINE declarations together in linux/percpu-defs.h so that they're in one place, and give them descriptive comments, particularly the SHARED_ALIGNED variant. It would be nice to collect these in linux/percpu.h, but that's not possible without sorting out the severe #include recursion between the x86 arch headers and the general headers (and possibly other arches too). Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
85 lines
2.9 KiB
C
85 lines
2.9 KiB
C
#ifndef _LINUX_PERCPU_DEFS_H
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#define _LINUX_PERCPU_DEFS_H
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/*
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* Determine the real variable name from the name visible in the
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* kernel sources.
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*/
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#define per_cpu_var(var) per_cpu__##var
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/*
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* Base implementations of per-CPU variable declarations and definitions, where
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* the section in which the variable is to be placed is provided by the
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* 'section' argument. This may be used to affect the parameters governing the
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* variable's storage.
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*
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* NOTE! The sections for the DECLARE and for the DEFINE must match, lest
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* linkage errors occur due the compiler generating the wrong code to access
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* that section.
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*/
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#define DECLARE_PER_CPU_SECTION(type, name, section) \
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extern \
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__attribute__((__section__(PER_CPU_BASE_SECTION section))) \
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PER_CPU_ATTRIBUTES __typeof__(type) per_cpu__##name
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#define DEFINE_PER_CPU_SECTION(type, name, section) \
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__attribute__((__section__(PER_CPU_BASE_SECTION section))) \
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PER_CPU_ATTRIBUTES __typeof__(type) per_cpu__##name
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/*
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* Variant on the per-CPU variable declaration/definition theme used for
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* ordinary per-CPU variables.
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*/
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#define DECLARE_PER_CPU(type, name) \
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DECLARE_PER_CPU_SECTION(type, name, "")
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#define DEFINE_PER_CPU(type, name) \
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DEFINE_PER_CPU_SECTION(type, name, "")
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/*
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* Declaration/definition used for per-CPU variables that must come first in
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* the set of variables.
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*/
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#define DECLARE_PER_CPU_FIRST(type, name) \
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DECLARE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
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#define DEFINE_PER_CPU_FIRST(type, name) \
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DEFINE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
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/*
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* Declaration/definition used for per-CPU variables that must be cacheline
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* aligned under SMP conditions so that, whilst a particular instance of the
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* data corresponds to a particular CPU, inefficiencies due to direct access by
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* other CPUs are reduced by preventing the data from unnecessarily spanning
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* cachelines.
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*
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* An example of this would be statistical data, where each CPU's set of data
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* is updated by that CPU alone, but the data from across all CPUs is collated
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* by a CPU processing a read from a proc file.
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*/
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#define DECLARE_PER_CPU_SHARED_ALIGNED(type, name) \
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DECLARE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
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____cacheline_aligned_in_smp
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#define DEFINE_PER_CPU_SHARED_ALIGNED(type, name) \
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DEFINE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
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____cacheline_aligned_in_smp
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/*
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* Declaration/definition used for per-CPU variables that must be page aligned.
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*/
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#define DECLARE_PER_CPU_PAGE_ALIGNED(type, name) \
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DECLARE_PER_CPU_SECTION(type, name, ".page_aligned")
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#define DEFINE_PER_CPU_PAGE_ALIGNED(type, name) \
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DEFINE_PER_CPU_SECTION(type, name, ".page_aligned")
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/*
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* Intermodule exports for per-CPU variables.
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*/
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#define EXPORT_PER_CPU_SYMBOL(var) EXPORT_SYMBOL(per_cpu__##var)
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#define EXPORT_PER_CPU_SYMBOL_GPL(var) EXPORT_SYMBOL_GPL(per_cpu__##var)
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#endif /* _LINUX_PERCPU_DEFS_H */
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