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Subject[PATCH 1/2] x86, percpu: Optimize this_cpu_ptr
Date
Allow arches to implement __this_cpu_ptr, and provide an x86 version.

Before:
movq $foo, %rax
movq %gs:this_cpu_off, %rdx
addq %rdx, %rax

After:
movq $foo, %rax
addq %gs:this_cpu_off, %rax

The benefit is doing it in one less instruction and not clobbering
a temporary register.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
---
arch/x86/include/asm/percpu.h | 11 +++++++++++
include/asm-generic/percpu.h | 9 +++++++--
2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index cd28f9a..845343e 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -47,6 +47,17 @@
#ifdef CONFIG_SMP
#define __percpu_arg(x) "%%"__stringify(__percpu_seg)":%P" #x
#define __my_cpu_offset percpu_read(this_cpu_off)
+
+/* shift a per-cpu pointer to the current cpu's version */
+#define __this_cpu_ptr(ptr) \
+({ \
+ typeof(ptr) __ptr = (ptr); \
+ __verify_pcpu_ptr(ptr); \
+ asm volatile("add " __percpu_arg(1) ", %0" \
+ : "+r" (__ptr) \
+ : "m" (this_cpu_off)); \
+ __ptr; \
+})
#else
#define __percpu_arg(x) "%P" #x
#endif
diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h
index b5043a9..5820fcb 100644
--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -60,9 +60,14 @@ extern unsigned long __per_cpu_offset[NR_CPUS];
#define __raw_get_cpu_var(var) \
(*SHIFT_PERCPU_PTR(&(var), __my_cpu_offset))

-#define this_cpu_ptr(ptr) SHIFT_PERCPU_PTR(ptr, my_cpu_offset)
+#ifndef __this_cpu_ptr
#define __this_cpu_ptr(ptr) SHIFT_PERCPU_PTR(ptr, __my_cpu_offset)
-
+#endif
+#ifdef CONFIG_DEBUG_PREEMPT
+#define this_cpu_ptr(ptr) SHIFT_PERCPU_PTR(ptr, my_cpu_offset)
+#else
+#define this_cpu_ptr(ptr) __this_cpu_ptr(ptr)
+#endif

#ifdef CONFIG_HAVE_SETUP_PER_CPU_AREA
extern void setup_per_cpu_areas(void);
--
1.7.2.2


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