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6dbde35308
It is an optimization and a cleanup, and adds the following new
generic percpu methods:
percpu_read()
percpu_write()
percpu_add()
percpu_sub()
percpu_and()
percpu_or()
percpu_xor()
and implements support for them on x86. (other architectures will fall
back to a default implementation)
The advantage is that for example to read a local percpu variable,
instead of this sequence:
return __get_cpu_var(var);
ffffffff8102ca2b: 48 8b 14 fd 80 09 74 mov -0x7e8bf680(,%rdi,8),%rdx
ffffffff8102ca32: 81
ffffffff8102ca33: 48 c7 c0 d8 59 00 00 mov $0x59d8,%rax
ffffffff8102ca3a: 48 8b 04 10 mov (%rax,%rdx,1),%rax
We can get a single instruction by using the optimized variants:
return percpu_read(var);
ffffffff8102ca3f: 65 48 8b 05 91 8f fd mov %gs:0x7efd8f91(%rip),%rax
I also cleaned up the x86-specific APIs and made the x86 code use
these new generic percpu primitives.
tj: * fixed generic percpu_sub() definition as Roel Kluin pointed out
* added percpu_and() for completeness's sake
* made generic percpu ops atomic against preemption
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Tejun Heo <tj@kernel.org>
135 lines
3.6 KiB
C
135 lines
3.6 KiB
C
#ifndef _ASM_GENERIC_PERCPU_H_
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#define _ASM_GENERIC_PERCPU_H_
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#include <linux/compiler.h>
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#include <linux/threads.h>
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/*
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* Determine the real variable name from the name visible in the
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* kernel sources.
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*/
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#define per_cpu_var(var) per_cpu__##var
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#ifdef CONFIG_SMP
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/*
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* per_cpu_offset() is the offset that has to be added to a
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* percpu variable to get to the instance for a certain processor.
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*
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* Most arches use the __per_cpu_offset array for those offsets but
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* some arches have their own ways of determining the offset (x86_64, s390).
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*/
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#ifndef __per_cpu_offset
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extern unsigned long __per_cpu_offset[NR_CPUS];
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#define per_cpu_offset(x) (__per_cpu_offset[x])
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#endif
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/*
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* Determine the offset for the currently active processor.
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* An arch may define __my_cpu_offset to provide a more effective
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* means of obtaining the offset to the per cpu variables of the
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* current processor.
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*/
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#ifndef __my_cpu_offset
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#define __my_cpu_offset per_cpu_offset(raw_smp_processor_id())
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#endif
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#ifdef CONFIG_DEBUG_PREEMPT
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#define my_cpu_offset per_cpu_offset(smp_processor_id())
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#else
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#define my_cpu_offset __my_cpu_offset
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#endif
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/*
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* Add a offset to a pointer but keep the pointer as is.
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*
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* Only S390 provides its own means of moving the pointer.
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*/
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#ifndef SHIFT_PERCPU_PTR
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#define SHIFT_PERCPU_PTR(__p, __offset) RELOC_HIDE((__p), (__offset))
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#endif
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/*
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* A percpu variable may point to a discarded regions. The following are
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* established ways to produce a usable pointer from the percpu variable
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* offset.
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*/
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#define per_cpu(var, cpu) \
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(*SHIFT_PERCPU_PTR(&per_cpu_var(var), per_cpu_offset(cpu)))
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#define __get_cpu_var(var) \
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(*SHIFT_PERCPU_PTR(&per_cpu_var(var), my_cpu_offset))
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#define __raw_get_cpu_var(var) \
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(*SHIFT_PERCPU_PTR(&per_cpu_var(var), __my_cpu_offset))
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#ifdef CONFIG_HAVE_SETUP_PER_CPU_AREA
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extern void setup_per_cpu_areas(void);
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#endif
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#else /* ! SMP */
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#define per_cpu(var, cpu) (*((void)(cpu), &per_cpu_var(var)))
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#define __get_cpu_var(var) per_cpu_var(var)
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#define __raw_get_cpu_var(var) per_cpu_var(var)
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#endif /* SMP */
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#ifndef PER_CPU_ATTRIBUTES
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#define PER_CPU_ATTRIBUTES
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#endif
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#define DECLARE_PER_CPU(type, name) extern PER_CPU_ATTRIBUTES \
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__typeof__(type) per_cpu_var(name)
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/*
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* Optional methods for optimized non-lvalue per-cpu variable access.
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*
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* @var can be a percpu variable or a field of it and its size should
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* equal char, int or long. percpu_read() evaluates to a lvalue and
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* all others to void.
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*
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* These operations are guaranteed to be atomic w.r.t. preemption.
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* The generic versions use plain get/put_cpu_var(). Archs are
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* encouraged to implement single-instruction alternatives which don't
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* require preemption protection.
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*/
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#ifndef percpu_read
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# define percpu_read(var) \
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({ \
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typeof(per_cpu_var(var)) __tmp_var__; \
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__tmp_var__ = get_cpu_var(var); \
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put_cpu_var(var); \
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__tmp_var__; \
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})
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#endif
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#define __percpu_generic_to_op(var, val, op) \
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do { \
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get_cpu_var(var) op val; \
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put_cpu_var(var); \
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} while (0)
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#ifndef percpu_write
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# define percpu_write(var, val) __percpu_generic_to_op(var, (val), =)
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#endif
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#ifndef percpu_add
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# define percpu_add(var, val) __percpu_generic_to_op(var, (val), +=)
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#endif
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#ifndef percpu_sub
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# define percpu_sub(var, val) __percpu_generic_to_op(var, (val), -=)
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#endif
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#ifndef percpu_and
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# define percpu_and(var, val) __percpu_generic_to_op(var, (val), &=)
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#endif
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#ifndef percpu_or
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# define percpu_or(var, val) __percpu_generic_to_op(var, (val), |=)
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#endif
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#ifndef percpu_xor
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# define percpu_xor(var, val) __percpu_generic_to_op(var, (val), ^=)
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#endif
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#endif /* _ASM_GENERIC_PERCPU_H_ */
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