linux-mips
[Top] [All Lists]

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

To: David Daney <ddaney@caviumnetworks.com>
Subject: Re: [PATCH 1/7] MIPS: add unlikely() to BUG_ON()
From: Coly Li <i@coly.li>
Date: Fri, 28 Jan 2011 18:41:41 +0800
Cc: Coly Li <bosong.ly@taobao.com>, linux-kernel@vger.kernel.org, Wang Cong <xiyou.wangcong@gmail.com>, Yong Zhang <yong.zhang0@gmail.com>, linux-mips <linux-mips@linux-mips.org>, Ralf Baechle <ralf@linux-mips.org>
Domainkey-signature: a=rsa-sha1; q=dns; c=nofws; s=default; d=coly.li; h=Received:Message-ID:Date:From:Reply-To:User-Agent:MIME-Version:To:CC:Subject:References:In-Reply-To:Content-Type:Content-Transfer-Encoding:X-Identified-User; b=EjQul+hhk9FsQdsoBpjtwSn5boF6GhRRmHf0P3cgK5OtNAxYRqUSOVOGpxUiv41xASt3AKVFzqDxI5fCe2iBSao1H0QBEzOXdY5GCnRl8J7+c9DIl1ovN94xMy9NYrCU;
In-reply-to: <4D41B06F.8070804@caviumnetworks.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <1296130356-29896-1-git-send-email-bosong.ly@taobao.com> <1296130356-29896-2-git-send-email-bosong.ly@taobao.com> <4D41B06F.8070804@caviumnetworks.com>
Reply-to: i@coly.li
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; zh-CN; rv:1.9.2.13) Gecko/20101206 SUSE/3.1.7 Thunderbird/3.1.7
On 2011年01月28日 01:50, David Daney Wrote:
Please Cc: linux-mips@linux-mips.org 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<bosong.ly@taobao.com>
Cc: David Daney<ddaney@caviumnetworks.com>
Cc: Wang Cong<xiyou.wangcong@gmail.com>
Cc: Yong Zhang<yong.zhang0@gmail.com>
---
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))


NAK.

__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

--
Coly Li

<Prev in Thread] Current Thread [Next in Thread>