LXR linux-bk/include/linux/percpu.h

   1#ifndef __LINUX_PERCPU_H
   2#define __LINUX_PERCPU_H
   3#include <linux/spinlock.h> /* For preempt_disable() */
   4#include <linux/slab.h> /* For kmalloc() */
   5#include <linux/smp.h>
   6#include <linux/string.h> /* For memset() */
   7#include <asm/percpu.h>
   8
   9/* Enough to cover all DEFINE_PER_CPUs in kernel, including modules. */
  10#ifndef PERCPU_ENOUGH_ROOM
  11#define PERCPU_ENOUGH_ROOM 32768
  12#endif
  13
  14/* Must be an lvalue. */
  15#define get_cpu_var(var) (*({ preempt_disable(); &__get_cpu_var(var); }))
  16#define put_cpu_var(var) preempt_enable()
  17
  18#ifdef CONFIG_SMP
  19
  20struct percpu_data {
  21        void *ptrs[NR_CPUS];
  22        void *blkp;
  23};
  24
  25/* 
  26 * Use this to get to a cpu's version of the per-cpu object allocated using
  27 * alloc_percpu.  If you want to get "this cpu's version", maybe you want
  28 * to use get_cpu_ptr... 
  29 */ 
  30#define per_cpu_ptr(ptr, cpu)                   \
  31({                                              \
  32        struct percpu_data *__p = (struct percpu_data *)~(unsigned long)(ptr); \
  33        (__typeof__(ptr))__p->ptrs[(cpu)];      \
  34})
  35
  36extern void *__alloc_percpu(size_t size, size_t align);
  37extern void free_percpu(const void *);
  38
  39#else /* CONFIG_SMP */
  40
  41#define per_cpu_ptr(ptr, cpu) (ptr)
  42
  43static inline void *__alloc_percpu(size_t size, size_t align)
  44{
  45        void *ret = kmalloc(size, GFP_KERNEL);
  46        if (ret)
  47                memset(ret, 0, size);
  48        return ret;
  49}
  50static inline void free_percpu(const void *ptr)
  51{       
  52        kfree(ptr);
  53}
  54
  55#endif /* CONFIG_SMP */
  56
  57/* Simple wrapper for the common case: zeros memory. */
  58#define alloc_percpu(type) \
  59        ((type *)(__alloc_percpu(sizeof(type), __alignof__(type))))
  60
  61/* 
  62 * Use these with alloc_percpu. If
  63 * 1. You want to operate on memory allocated by alloc_percpu (dereference
  64 *    and read/modify/write)  AND 
  65 * 2. You want "this cpu's version" of the object AND 
  66 * 3. You want to do this safely since:
  67 *    a. On multiprocessors, you don't want to switch between cpus after 
  68 *    you've read the current processor id due to preemption -- this would 
  69 *    take away the implicit  advantage to not have any kind of traditional 
  70 *    serialization for per-cpu data
  71 *    b. On uniprocessors, you don't want another kernel thread messing
  72 *    up with the same per-cpu data due to preemption
  73 *    
  74 * So, Use get_cpu_ptr to disable preemption and get pointer to the 
  75 * local cpu version of the per-cpu object. Use put_cpu_ptr to enable
  76 * preemption.  Operations on per-cpu data between get_ and put_ is
  77 * then considered to be safe. And ofcourse, "Thou shalt not sleep between 
  78 * get_cpu_ptr and put_cpu_ptr"
  79 */
  80#define get_cpu_ptr(ptr) per_cpu_ptr(ptr, get_cpu())
  81#define put_cpu_ptr(ptr) put_cpu()
  82
  83#endif /* __LINUX_PERCPU_H */
  84