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authorDavid Howells <dhowells@redhat.com>2009-04-21 23:00:29 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2009-04-21 19:40:00 -0700
commit5028eaa97dd1dab9cd7c30c4d38f71c708ca64bc (patch)
treeff416e9ecb00ab2b616bce6acc4e2579c45b06b9 /include
parent9b8de7479d0dbab1ed98b5b015d44232c9d3d08e (diff)
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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 <dhowells@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/asm-generic/percpu.h26
-rw-r--r--include/linux/percpu-defs.h84
-rw-r--r--include/linux/percpu.h20
3 files changed, 86 insertions, 44 deletions
diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h
index af47b9e1006..d7d50d7ee51 100644
--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -1,13 +1,9 @@
#ifndef _ASM_GENERIC_PERCPU_H_
#define _ASM_GENERIC_PERCPU_H_
+
#include <linux/compiler.h>
#include <linux/threads.h>
-
-/*
- * Determine the real variable name from the name visible in the
- * kernel sources.
- */
-#define per_cpu_var(var) per_cpu__##var
+#include <linux/percpu-defs.h>
#ifdef CONFIG_SMP
@@ -101,22 +97,4 @@ extern void setup_per_cpu_areas(void);
#define PER_CPU_ATTRIBUTES
#endif
-#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 DECLARE_PER_CPU(type, name) \
- DECLARE_PER_CPU_SECTION(type, name, "")
-
-#define DECLARE_PER_CPU_SHARED_ALIGNED(type, name) \
- DECLARE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
- ____cacheline_aligned_in_smp
-
-#define DECLARE_PER_CPU_PAGE_ALIGNED(type, name) \
- DECLARE_PER_CPU_SECTION(type, name, ".page_aligned")
-
-#define DECLARE_PER_CPU_FIRST(type, name) \
- DECLARE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
-
#endif /* _ASM_GENERIC_PERCPU_H_ */
diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h
new file mode 100644
index 00000000000..8f921d74f49
--- /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 */
diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index f052d818499..1581ff235c7 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -9,26 +9,6 @@
#include <asm/percpu.h>
-#define DEFINE_PER_CPU_SECTION(type, name, section) \
- __attribute__((__section__(PER_CPU_BASE_SECTION section))) \
- PER_CPU_ATTRIBUTES __typeof__(type) per_cpu__##name
-
-#define DEFINE_PER_CPU(type, name) \
- DEFINE_PER_CPU_SECTION(type, name, "")
-
-#define DEFINE_PER_CPU_SHARED_ALIGNED(type, name) \
- DEFINE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
- ____cacheline_aligned_in_smp
-
-#define DEFINE_PER_CPU_PAGE_ALIGNED(type, name) \
- DEFINE_PER_CPU_SECTION(type, name, ".page_aligned")
-
-#define DEFINE_PER_CPU_FIRST(type, name) \
- DEFINE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
-
-#define EXPORT_PER_CPU_SYMBOL(var) EXPORT_SYMBOL(per_cpu__##var)
-#define EXPORT_PER_CPU_SYMBOL_GPL(var) EXPORT_SYMBOL_GPL(per_cpu__##var)
-
/* enough to cover all DEFINE_PER_CPUs in modules */
#ifdef CONFIG_MODULES
#define PERCPU_MODULE_RESERVE (8 << 10)