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    SubjectRe: [PATCH 2/7] PowerPC: add unlikely() to BUG_ON()
    Why not also CC the PPC maintainers as well?  I am not certain, but I 
    think they may be reached at:

    linuxppc-dev@lists.ozlabs.org


    On 01/27/2011 04:12 AM, Coly Li wrote:
    > Current BUG_ON() arch/powerpc/include/asm/bug.h does not use unlikely(),
    > in order to get better branch predict result, source code may have to call
    > BUG_ON() with unlikely() explicitly. This is not a suggested method
    > to use BUG_ON().
    >
    > This patch adds unlikely() inside BUG_ON implementation on PPC
    > code, callers can use BUG_ON without explicit unlikely() now.
    >
    > I don't have any PPC hardware to compile and test this fix, any feedback
    > of this patch is welcome.
    >
    > Signed-off-by: Coly Li<bosong.ly@taobao.com>
    > Cc: Jeremy Fitzhardinge<jeremy@goop.org>
    > Cc: David Daney<ddaney@caviumnetworks.com>
    > Cc: Wang Cong<xiyou.wangcong@gmail.com>
    > Cc: Yong Zhang<yong.zhang0@gmail.com>
    > diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
    > index 065c590..10889a6 100644
    > --- a/arch/powerpc/include/asm/bug.h
    > +++ b/arch/powerpc/include/asm/bug.h
    > @@ -2,6 +2,7 @@
    > #define _ASM_POWERPC_BUG_H
    > #ifdef __KERNEL__
    >
    > +#include<linux/compiler.h>
    > #include<asm/asm-compat.h>
    >
    > /*
    > @@ -71,7 +72,7 @@
    > unreachable(); \
    > } while (0)
    >
    > -#define BUG_ON(x) do { \
    > +#define __BUG_ON(x) do { \
    > if (__builtin_constant_p(x)) { \
    > if (x) \
    > BUG(); \
    > @@ -85,6 +86,8 @@
    > } \
    > } while (0)
    >
    > +#define BUG_ON(x) __BUG_ON(unlikely(x))
    > +

    This is the same type of frobbing you were trying to do to MIPS.

    I will let the powerpc maintainers weigh in on it, but my opinion is
    that, as with MIPS, BUG_ON() is expanded to a single machine
    instruction, and this unlikely() business will not change the generated
    code in any useful way. It is thus gratuitous code churn and
    complexification.

    David Daney

    > #define __WARN_TAINT(taint) do { \
    > __asm__ __volatile__( \
    > "1: twi 31,0,0\n" \



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