linux/include/asm-generic/local.h
Kyle McMartin f5f5370da4 [PATCH] Decrapify asm-generic/local.h
Now that Christoph Lameter's atomic_long_t support is merged in mainline,
might as well convert asm-generic/local.h to use it, so the same code can
be used for both sizes of 32 and 64-bit unsigned longs.

akpm sayeth:

Q:

  Is there any particular reason why these routines weren't simply
  implemented with local_save/restore_flags, if they are only meant to
  guarantee atomicity to the local cpu?  I'm sure on most platforms this
  would be more efficient than using an atomic...

A:

  The whole _point_ of local_t is to avoid local_irq_disable().  It's
  designed to exploit the fact that many CPUs can do incs and decs in a way
  which is atomic wrt local interrupts, but not atomic wrt SMP.

But this patch makes sense, because asm-generic/local.h is just a fallback
implementation for architectures which either cannot perform these
local-irq-atomic operations, or its maintainers haven't yet got around to
implementing them.

We need more work done on local_t in the 2.6.17 timeframe - they're defined as
unsigned long, but some architectures implement them as signed long.

Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-03-28 09:16:01 -08:00

57 lines
2.1 KiB
C

#ifndef _ASM_GENERIC_LOCAL_H
#define _ASM_GENERIC_LOCAL_H
#include <linux/config.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <asm/atomic.h>
#include <asm/types.h>
/* An unsigned long type for operations which are atomic for a single
* CPU. Usually used in combination with per-cpu variables. */
/* Implement in terms of atomics. */
/* Don't use typedef: don't want them to be mixed with atomic_t's. */
typedef struct
{
atomic_long_t a;
} local_t;
#define LOCAL_INIT(i) { ATOMIC_LONG_INIT(i) }
#define local_read(l) ((unsigned long)atomic_long_read(&(l)->a))
#define local_set(l,i) atomic_long_set((&(l)->a),(i))
#define local_inc(l) atomic_long_inc(&(l)->a)
#define local_dec(l) atomic_long_dec(&(l)->a)
#define local_add(i,l) atomic_long_add((i),(&(l)->a))
#define local_sub(i,l) atomic_long_sub((i),(&(l)->a))
/* Non-atomic variants, ie. preemption disabled and won't be touched
* in interrupt, etc. Some archs can optimize this case well. */
#define __local_inc(l) local_set((l), local_read(l) + 1)
#define __local_dec(l) local_set((l), local_read(l) - 1)
#define __local_add(i,l) local_set((l), local_read(l) + (i))
#define __local_sub(i,l) local_set((l), local_read(l) - (i))
/* Use these for per-cpu local_t variables: on some archs they are
* much more efficient than these naive implementations. Note they take
* a variable (eg. mystruct.foo), not an address.
*/
#define cpu_local_read(v) local_read(&__get_cpu_var(v))
#define cpu_local_set(v, i) local_set(&__get_cpu_var(v), (i))
#define cpu_local_inc(v) local_inc(&__get_cpu_var(v))
#define cpu_local_dec(v) local_dec(&__get_cpu_var(v))
#define cpu_local_add(i, v) local_add((i), &__get_cpu_var(v))
#define cpu_local_sub(i, v) local_sub((i), &__get_cpu_var(v))
/* Non-atomic increments, ie. preemption disabled and won't be touched
* in interrupt, etc. Some archs can optimize this case well.
*/
#define __cpu_local_inc(v) __local_inc(&__get_cpu_var(v))
#define __cpu_local_dec(v) __local_dec(&__get_cpu_var(v))
#define __cpu_local_add(i, v) __local_add((i), &__get_cpu_var(v))
#define __cpu_local_sub(i, v) __local_sub((i), &__get_cpu_var(v))
#endif /* _ASM_GENERIC_LOCAL_H */