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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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