Commit f5f5370d authored by Kyle McMartin's avatar Kyle McMartin Committed by Linus Torvalds
Browse files

[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: default avatarKyle McMartin <kyle@parisc-linux.org>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 4f3a36a7
......@@ -4,28 +4,28 @@
#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. */
#if BITS_PER_LONG == 32
/* Implement in terms of atomics. */
/* Don't use typedef: don't want them to be mixed with atomic_t's. */
typedef struct
{
atomic_t a;
atomic_long_t a;
} local_t;
#define LOCAL_INIT(i) { ATOMIC_INIT(i) }
#define LOCAL_INIT(i) { ATOMIC_LONG_INIT(i) }
#define local_read(l) ((unsigned long)atomic_read(&(l)->a))
#define local_set(l,i) atomic_set((&(l)->a),(i))
#define local_inc(l) atomic_inc(&(l)->a)
#define local_dec(l) atomic_dec(&(l)->a)
#define local_add(i,l) atomic_add((i),(&(l)->a))
#define local_sub(i,l) atomic_sub((i),(&(l)->a))
#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. */
......@@ -34,68 +34,6 @@ typedef struct
#define __local_add(i,l) local_set((l), local_read(l) + (i))
#define __local_sub(i,l) local_set((l), local_read(l) - (i))
#else /* ... can't use atomics. */
/* Implement in terms of three variables.
Another option would be to use local_irq_save/restore. */
typedef struct
{
/* 0 = in hardirq, 1 = in softirq, 2 = usermode. */
unsigned long v[3];
} local_t;
#define _LOCAL_VAR(l) ((l)->v[!in_interrupt() + !in_irq()])
#define LOCAL_INIT(i) { { (i), 0, 0 } }
static inline unsigned long local_read(local_t *l)
{
return l->v[0] + l->v[1] + l->v[2];
}
static inline void local_set(local_t *l, unsigned long v)
{
l->v[0] = v;
l->v[1] = l->v[2] = 0;
}
static inline void local_inc(local_t *l)
{
preempt_disable();
_LOCAL_VAR(l)++;
preempt_enable();
}
static inline void local_dec(local_t *l)
{
preempt_disable();
_LOCAL_VAR(l)--;
preempt_enable();
}
static inline void local_add(unsigned long v, local_t *l)
{
preempt_disable();
_LOCAL_VAR(l) += v;
preempt_enable();
}
static inline void local_sub(unsigned long v, local_t *l)
{
preempt_disable();
_LOCAL_VAR(l) -= v;
preempt_enable();
}
/* 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) ((l)->v[0]++)
#define __local_dec(l) ((l)->v[0]--)
#define __local_add(i,l) ((l)->v[0] += (i))
#define __local_sub(i,l) ((l)->v[0] -= (i))
#endif /* Non-atomic implementation */
/* 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.
......
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