Re: [PATCH 1/7] MIPS: add unlikely() to BUG_ON()

From: Coly Li
Date: Fri Jan 28 2011 - 05:15:52 EST

On 2011å01æ28æ 01:50, David Daney Wrote:
Please Cc: linux-mips@xxxxxxxxxxxxxx for MIPS patches.

On 01/27/2011 04:12 AM, Coly Li wrote:
Current BUG_ON() in arch/mips/include/asm/bug.h does not use unlikely(),
in order to get better branch predict result, source code should 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 MIPS code,
callers can use BUG_ON without explicit unlikely() now.

I have no usable MIPS hardware to build and test the fix, any test result
of this patch is welcome.

Signed-off-by: Coly Li<>
Cc: David Daney<ddaney@xxxxxxxxxxxxxxxxxx>
Cc: Wang Cong<xiyou.wangcong@xxxxxxxxx>
Cc: Yong Zhang<yong.zhang0@xxxxxxxxx>
arch/mips/include/asm/bug.h | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/mips/include/asm/bug.h b/arch/mips/include/asm/bug.h
index 540c98a..6771c07 100644
--- a/arch/mips/include/asm/bug.h
+++ b/arch/mips/include/asm/bug.h
@@ -30,7 +30,7 @@ static inline void __BUG_ON(unsigned long condition)
: : "r" (condition), "i" (BRK_BUG));

-#define BUG_ON(C) __BUG_ON((unsigned long)(C))
+#define BUG_ON(C) __BUG_ON((unsigned long)unlikely(C))


__BUG_ON() expands to a single instruction. Frobbing about with unlikely() will have no effect on the generated code and
is thus gratuitous code churn.

Since unlikely() in arch implemented BUG_ON() is gratuitous, using unlikely() in kernel code like BUG_ON(unlikely(...)) for arch implemented BUG_ON is unwelcome neither.

The NAK makes sense, thanks for your reply.


Coly Li
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