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Subject[PATCH 03/10] percpu: Make the asm-generic/percpu.h more "generic"
V1->V2:
- add support for PER_CPU_ATTRIBUTES

V2->V3:
- fix generic smp percpu_modcopy to use per_cpu_offset() macro.

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_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 <rusty@rustcorp.com.au>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Mike Travis <travis@sgi.com>

---
arch/ia64/kernel/module.c | 2 -
include/asm-generic/percpu.h | 74 ++++++++++++++++++++++++++++++++++++-------
2 files changed, 64 insertions(+), 12 deletions(-)

--- a/arch/ia64/kernel/module.c
+++ b/arch/ia64/kernel/module.c
@@ -947,7 +947,7 @@ percpu_modcopy (void *pcpudst, const voi
{
unsigned int i;
for_each_possible_cpu(i) {
- memcpy(pcpudst + __per_cpu_offset[i], src, size);
+ memcpy(pcpudst + per_cpu_offset(i), src, size);
}
}
#endif /* CONFIG_SMP */
--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -3,35 +3,87 @@
#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
+
#ifdef CONFIG_SMP

+/*
+ * 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])
+#endif

-/* 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())
+#else
+#define my_cpu_offset __my_cpu_offset
+#endif
+
+/*
+ * Add a offset to a pointer but keep the pointer as is.
+ *
+ * Only S390 provides its own means of moving the pointer.
+ */
+#ifndef SHIFT_PERCPU_PTR
+#define SHIFT_PERCPU_PTR(__p, __offset) RELOC_HIDE((__p), (__offset))
+#endif
+
+/*
+ * 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))
+
+
+#ifdef CONFIG_ARCH_SETS_UP_PER_CPU_AREA
+extern void setup_per_cpu_areas(void);
+#endif

/* A macro to avoid #include hell... */
#define percpu_modcopy(pcpudst, src, size) \
do { \
unsigned int __i; \
for_each_possible_cpu(__i) \
- memcpy((pcpudst)+__per_cpu_offset[__i], \
+ memcpy((pcpudst)+per_cpu_offset(__i), \
(src), (size)); \
} while (0)
#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
+#ifndef PER_CPU_ATTRIBUTES
+#define PER_CPU_ATTRIBUTES
+#endif
+
+#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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