From 5028eaa97dd1dab9cd7c30c4d38f71c708ca64bc Mon Sep 17 00:00:00 2001 From: David Howells Date: Tue, 21 Apr 2009 23:00:29 +0100 Subject: PERCPU: Collect the DECLARE/DEFINE declarations together 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 Signed-off-by: Linus Torvalds --- include/linux/percpu-defs.h | 84 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 84 insertions(+) create mode 100644 include/linux/percpu-defs.h (limited to 'include/linux/percpu-defs.h') diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h new file mode 100644 index 000000000000..8f921d74f49f --- /dev/null +++ b/include/linux/percpu-defs.h @@ -0,0 +1,84 @@ +#ifndef _LINUX_PERCPU_DEFS_H +#define _LINUX_PERCPU_DEFS_H + +/* + * Determine the real variable name from the name visible in the + * kernel sources. + */ +#define per_cpu_var(var) per_cpu__##var + +/* + * Base implementations of per-CPU variable declarations and definitions, where + * the section in which the variable is to be placed is provided by the + * 'section' argument. This may be used to affect the parameters governing the + * variable's storage. + * + * NOTE! The sections for the DECLARE and for the DEFINE must match, lest + * linkage errors occur due the compiler generating the wrong code to access + * that section. + */ +#define DECLARE_PER_CPU_SECTION(type, name, section) \ + extern \ + __attribute__((__section__(PER_CPU_BASE_SECTION section))) \ + PER_CPU_ATTRIBUTES __typeof__(type) per_cpu__##name + +#define DEFINE_PER_CPU_SECTION(type, name, section) \ + __attribute__((__section__(PER_CPU_BASE_SECTION section))) \ + PER_CPU_ATTRIBUTES __typeof__(type) per_cpu__##name + +/* + * Variant on the per-CPU variable declaration/definition theme used for + * ordinary per-CPU variables. + */ +#define DECLARE_PER_CPU(type, name) \ + DECLARE_PER_CPU_SECTION(type, name, "") + +#define DEFINE_PER_CPU(type, name) \ + DEFINE_PER_CPU_SECTION(type, name, "") + +/* + * Declaration/definition used for per-CPU variables that must come first in + * the set of variables. + */ +#define DECLARE_PER_CPU_FIRST(type, name) \ + DECLARE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION) + +#define DEFINE_PER_CPU_FIRST(type, name) \ + DEFINE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION) + +/* + * Declaration/definition used for per-CPU variables that must be cacheline + * aligned under SMP conditions so that, whilst a particular instance of the + * data corresponds to a particular CPU, inefficiencies due to direct access by + * other CPUs are reduced by preventing the data from unnecessarily spanning + * cachelines. + * + * An example of this would be statistical data, where each CPU's set of data + * is updated by that CPU alone, but the data from across all CPUs is collated + * by a CPU processing a read from a proc file. + */ +#define DECLARE_PER_CPU_SHARED_ALIGNED(type, name) \ + DECLARE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \ + ____cacheline_aligned_in_smp + +#define DEFINE_PER_CPU_SHARED_ALIGNED(type, name) \ + DEFINE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \ + ____cacheline_aligned_in_smp + +/* + * Declaration/definition used for per-CPU variables that must be page aligned. + */ +#define DECLARE_PER_CPU_PAGE_ALIGNED(type, name) \ + DECLARE_PER_CPU_SECTION(type, name, ".page_aligned") + +#define DEFINE_PER_CPU_PAGE_ALIGNED(type, name) \ + DEFINE_PER_CPU_SECTION(type, name, ".page_aligned") + +/* + * Intermodule exports for per-CPU variables. + */ +#define EXPORT_PER_CPU_SYMBOL(var) EXPORT_SYMBOL(per_cpu__##var) +#define EXPORT_PER_CPU_SYMBOL_GPL(var) EXPORT_SYMBOL_GPL(per_cpu__##var) + + +#endif /* _LINUX_PERCPU_DEFS_H */ -- cgit v1.2.3