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Subject[PATCH 03/10] percpu: Make the asm-generic/percpu.h more "generic"
Add the ability to use generic/percpu even if the arch needs to override
several aspects of its operations. This will enable the use of generic
percpu.h for all arches.

An arch may define:

__per_cpu_offset Do not use the generic pointer array. Arch must
define per_cpu_offset(cpu) (used by x86_64, s390).

__my_cpu_offset Can be defined to provide an optimized way to determine
the offset for variables of the currently executing
processor. Used by ia64, x86_64, x86_32, sparc64, s/390.

SHIFT_PERCPU_PTR(ptr, offset) If an arch defines it then special handling
of pointer arithmentic may be implemented. Used
by s/390.

(Some of these special percpu arch implementations may be later consolidated
so that there are less cases to deal with.)

Cc: Rusty Russell <>
Cc: Andi Kleen <>
Signed-off-by: Christoph Lameter <>
Signed-off-by: Mike Travis <>


- add support for PER_CPU_ATTRIBUTES

- fix generic smp percpu_modcopy to use per_cpu_offset() macro.

include/asm-generic/percpu.h | 72 +++++++++++++++++++++++++++++++++++++------
1 file changed, 62 insertions(+), 10 deletions(-)

--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -3,27 +3,79 @@
#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

+ * per_cpu_offset() is the offset that has to be added to a
+ * percpu variable to get to the instance for a certain processor.
+ *
+ * Most arches use the __per_cpu_offset array for those offsets but
+ * some arches have their own ways of determining the offset (x86_64, s390).
+ */
+#ifndef __per_cpu_offset
extern unsigned long __per_cpu_offset[NR_CPUS];

#define per_cpu_offset(x) (__per_cpu_offset[x])

-/* var is in discarded region: offset to particular copy we want */
-#define per_cpu(var, cpu) (*({ \
- extern int simple_identifier_##var(void); \
- RELOC_HIDE(&per_cpu__##var, __per_cpu_offset[cpu]); }))
-#define __get_cpu_var(var) per_cpu(var, smp_processor_id())
-#define __raw_get_cpu_var(var) per_cpu(var, raw_smp_processor_id())
+ * Determine the offset for the currently active processor.
+ * An arch may define __my_cpu_offset to provide a more effective
+ * means of obtaining the offset to the per cpu variables of the
+ * current processor.
+ */
+#ifndef __my_cpu_offset
+#define __my_cpu_offset per_cpu_offset(raw_smp_processor_id())
+#define my_cpu_offset per_cpu_offset(smp_processor_id())
+#define my_cpu_offset __my_cpu_offset
+ * Add a offset to a pointer but keep the pointer as is.
+ *
+ * Only S390 provides its own means of moving the pointer.
+ */
+#define SHIFT_PERCPU_PTR(__p, __offset) RELOC_HIDE((__p), (__offset))
+ * A percpu variable may point to a discarded reghions. The following are
+ * established ways to produce a usable pointer from the percpu variable
+ * offset.
+ */
+#define per_cpu(var, cpu) \
+ (*SHIFT_PERCPU_PTR(&per_cpu_var(var), per_cpu_offset(cpu)))
+#define __get_cpu_var(var) \
+ (*SHIFT_PERCPU_PTR(&per_cpu_var(var), my_cpu_offset))
+#define __raw_get_cpu_var(var) \
+ (*SHIFT_PERCPU_PTR(&per_cpu_var(var), __my_cpu_offset))
+extern void setup_per_cpu_areas(void);

#else /* ! SMP */

-#define per_cpu(var, cpu) (*((void)(cpu), &per_cpu__##var))
-#define __get_cpu_var(var) per_cpu__##var
-#define __raw_get_cpu_var(var) per_cpu__##var
+#define per_cpu(var, cpu) (*((void)(cpu), &per_cpu_var(var)))
+#define __get_cpu_var(var) per_cpu_var(var)
+#define __raw_get_cpu_var(var) per_cpu_var(var)

#endif /* SMP */

-#define DECLARE_PER_CPU(type, name) extern __typeof__(type) per_cpu__##name
+#define DECLARE_PER_CPU(type, name) extern PER_CPU_ATTRIBUTES \
+ __typeof__(type) per_cpu_var(name)

#endif /* _ASM_GENERIC_PERCPU_H_ */

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