alloc_percpu: read_percpu_var / read_percpu_ptr Impact: New API get_cpu_var/get_cpu_ptr return lvalues, but for ia64 and x86/32 (and one day x86/64) there are more efficient ways if you just want an rvalue. The x86-specific versions have proven popular in that arch, so I expect they'll be popular generally. So introduce read_percpu_var and read_percpu_ptr. They are separate, because when we enlarge percpu areas IA64 is not going to be able to do its trick on abitrary per-cpu pointers, only vars (which are in the first 64k). Signed-off-by: Rusty Russell --- arch/alpha/include/asm/percpu.h | 4 ++++ arch/ia64/include/asm/percpu.h | 1 + arch/x86/include/asm/percpu.h | 4 ++++ include/asm-generic/percpu.h | 24 ++++++++++++++++++++++++ 4 files changed, 33 insertions(+) diff --git a/arch/alpha/include/asm/percpu.h b/arch/alpha/include/asm/percpu.h --- a/arch/alpha/include/asm/percpu.h +++ b/arch/alpha/include/asm/percpu.h @@ -62,6 +62,7 @@ extern unsigned long __per_cpu_offset[NR (*SHIFT_PERCPU_PTR(var, my_cpu_offset)) #define __raw_get_cpu_var(var) \ (*SHIFT_PERCPU_PTR(var, __my_cpu_offset)) +#define read_percpu_var(var) (0, __raw_get_cpu_var(var)) #define __get_cpu_ptr(ptr) \ RELOC_HIDE(ptr, my_cpu_offset) #define __raw_get_cpu_ptr(ptr) \ @@ -72,15 +73,18 @@ extern unsigned long __per_cpu_offset[NR RELOC_HIDE(ptr, my_cpu_offset) #define __raw_get_cpu_ptr(ptr) \ RELOC_HIDE(ptr, __my_cpu_offset) +#define read_percpu_ptr(ptr) (0, *__raw_get_cpu_ptr(ptr)) #else /* ! SMP */ #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) +#define read_percpu_var(var) (0, per_cpu_var(var)) #define per_cpu_ptr(ptr, cpu) (ptr) #define __get_cpu_ptr(ptr) (ptr) #define __raw_get_cpu_ptr(ptr) (ptr) +#define read_percpu_ptr(ptr) (0, *(ptr)) #define PER_CPU_ATTRIBUTES diff --git a/arch/ia64/include/asm/percpu.h b/arch/ia64/include/asm/percpu.h --- a/arch/ia64/include/asm/percpu.h +++ b/arch/ia64/include/asm/percpu.h @@ -40,6 +40,7 @@ extern void *per_cpu_init(void); * more efficient. */ #define __ia64_per_cpu_var(var) per_cpu__##var +#define read_percpu_var(var) (0, __ia64_per_cpu_var(var)) #include diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h --- a/arch/x86/include/asm/percpu.h +++ b/arch/x86/include/asm/percpu.h @@ -101,6 +101,10 @@ DECLARE_PER_CPU(struct x8664_pda, pda); #define __percpu_seg "" #endif /* SMP */ + +/* Define these now so asm-generic/percpu.h doesn't. */ +#define read_percpu_var(var) x86_read_percpu(var) +#define read_percpu_ptr(ptr) x86_read_percpu(*(ptr)) #include diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h --- a/include/asm-generic/percpu.h +++ b/include/asm-generic/percpu.h @@ -60,6 +60,17 @@ extern unsigned long __per_cpu_offset[NR #define __raw_get_cpu_var(var) \ (*SHIFT_PERCPU_PTR(&per_cpu_var(var), __my_cpu_offset)) +#ifndef read_percpu_var +/** + * read_percpu_var - get a copy of this cpu's percpu simple var. + * @var: the name of the per-cpu variable. + * + * Like __raw_get_cpu_var(), but doesn't provide an lvalue. Some platforms + * can do this more efficiently (x86/32). Only works on fundamental types. + */ +#define read_percpu_var(var) (0, __raw_get_cpu_var(var)) +#endif /* read_percpu_var */ + /* Use RELOC_HIDE: some arch's SHIFT_PERCPU_PTR really want an identifier. */ /** * per_cpu_ptr - get a pointer to a particular cpu's allocated memory @@ -81,6 +92,17 @@ extern unsigned long __per_cpu_offset[NR #define __get_cpu_ptr(ptr) RELOC_HIDE(ptr, my_cpu_offset) #define __raw_get_cpu_ptr(ptr) RELOC_HIDE(ptr, __my_cpu_offset) +#ifndef read_percpu_ptr +/** + * read_percpu_ptr - deref this cpu's simple percpu pointer. + * @ptr: the address of the per-cpu variable. + * + * Like read_percpu_var(), but can be used on pointers returned from + * alloc_percpu. + */ +#define read_percpu_ptr(ptr) (0, *__raw_get_cpu_ptr(ptr)) +#endif /* read_percpu_ptr */ + #ifdef CONFIG_HAVE_SETUP_PER_CPU_AREA extern void setup_per_cpu_areas(void); #endif @@ -90,9 +112,11 @@ extern void setup_per_cpu_areas(void); #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) +#define read_percpu_var(var) (0, per_cpu_var(var)) #define per_cpu_ptr(ptr, cpu) (ptr) #define __get_cpu_ptr(ptr) (ptr) #define __raw_get_cpu_ptr(ptr) (ptr) +#define read_percpu_ptr(ptr) (0, *(ptr)) #endif /* SMP */