Le mercredi 10 novembre 2010 Ã 09:40 -0600, Christoph Lameter a Ãcrit :
> Tried it. This is the result.
>
>
> Implement this_cpu_add_return and friends and supply an optimized
> implementation for x86.
>
> Use this_cpu_add_return for vmstats and nmi processing.
>
> There is no win in terms of code size (stays the same because xadd is a
> longer instruction thaninc and requires loading a constant in a register first)
> but we eliminate one memory access.
>
> Plus we introduce a more flexible way of per cpu atomic operations.
>
> Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>
>
> ---
I believe this new xx_return stuff would be useful on x86_32 :
#if defined(CONFIG_HIGHMEM) || defined(CONFIG_X86_32)
kmap_atomic_idx_push() / kmap_atomic_idx_pop() are a bit expensive
because :
c102a652: 0f 01 3b invlpg (%ebx)
int idx = --__get_cpu_var(__kmap_atomic_idx);
c102a655: 64 03 3d 90 40 5f c1 add %fs:0xc15f4090,%edi
c102a65c: 8b 07 mov (%edi),%eax
c102a65e: 83 e8 01 sub $0x1,%eax
c102a661: 85 c0 test %eax,%eax
c102a663: 89 07 mov %eax,(%edi)
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index b676c58..bb5db26 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -91,7 +91,7 @@ static inline int kmap_atomic_idx_push(void)
static inline int kmap_atomic_idx(void)
{
- return __get_cpu_var(__kmap_atomic_idx) - 1;
+ return __this_cpu_read(__kmap_atomic_idx) - 1;
}
static inline int kmap_atomic_idx_pop(void)
--
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