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SubjectRe: [RFC local_t removal V1 3/4] Optimized add_local()
* Christoph Lameter (cl@linux-foundation.org) wrote:
> Use XADD to implement add_local().

xadd should only be used to implement add_local_return, not add_local.

add_local can be implemented with the "add" instruction, which is
significantly faster if my memory serves me correctly.

Thanks,

Mathieu

>
> Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
>
> ---
> arch/x86/include/asm/add-local.h | 56 ++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 55 insertions(+), 1 deletion(-)
>
> Index: linux-2.6/arch/x86/include/asm/add-local.h
> ===================================================================
> --- linux-2.6.orig/arch/x86/include/asm/add-local.h 2010-01-05 15:29:11.000000000 -0600
> +++ linux-2.6/arch/x86/include/asm/add-local.h 2010-01-05 15:33:59.000000000 -0600
> @@ -1,2 +1,56 @@
> -#include <asm-generic/add-local.h>
> +#ifndef __ASM_X86_ADD_LOCAL_H
> +#define __ASM_X86_ADD_LOCAL_H
> +
> +#include <linux/types.h>
> +#include <asm-generic/add-local-generic.h>
> +
> +static inline unsigned long __add_return_local(volatile void *ptr,
> + unsigned long value, int size)
> +{
> + unsigned long r;
> +
> +#ifdef CONFIG_M386
> + if (unlikely(boot_cpu_data.x86 <= 3))
> + return __add_return_local_generic(ptr, value, size);
> +#endif
> +
> + /*
> + * Sanity checking, compile-time.
> + */
> + if (size == 8 && sizeof(unsigned long) != 8)
> + wrong_size_add_local(ptr);
> +
> + r = value;
> + switch (size) {
> + case 1:
> + asm volatile("xaddb %0, %1;": "+r" (r), "+m" (*((u8 *)ptr)):
> + : "memory");
> + break;
> + case 2:
> + asm volatile("xaddw %0, %1;": "+r" (r), "+m" (*((u16 *)ptr)):
> + : "memory");
> + break;
> + case 4:
> + asm volatile("xaddl %0, %1;": "+r" (r), "+m" (*((u32 *)ptr)):
> + : "memory");
> + break;
> + case 8:
> + asm volatile("xaddq %0, %1;": "+r" (r), "+m" (*((u64 *)ptr)):
> + : "memory");
> + break;
> + default:
> + wrong_size_add_local(ptr);
> + }
> + return r + value;
> +}
> +
> +#define add_return_local(ptr, v) \
> + ((__typeof__(*(ptr)))__add_return_local((ptr), (unsigned long)(v), \
> + sizeof(*(ptr))))
> +
> +#define add_local(ptr, v) (void)__add_return_local((ptr), (unsigned long)(v), \
> + sizeof(*(ptr)))
> +
> +
> +#endif
>
>
> --

--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


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