linux-kernel - Re: [PATCH 2/7] PowerPC: add unlikely() to BUG

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Message-ID: <4D42A23B.4090302@coly.li>
Date:	Fri, 28 Jan 2011 19:02:19 +0800
From:	Coly Li <i@...y.li>
To:	Andreas Schwab <schwab@...hat.com>
CC:	David Laight <David.Laight@...LAB.COM>,
	David Daney <ddaney@...iumnetworks.com>,
	Coly Li <bosong.ly@...bao.com>,
	Wang Cong <xiyou.wangcong@...il.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	Yong Zhang <yong.zhang0@...il.com>
Subject: Re: [PATCH 2/7] PowerPC: add unlikely() to BUG_ON()

On 2011年01月28日 18:14, Andreas Schwab Wrote:
> "David Laight"<David.Laight@...LAB.COM>  writes:
>
>> Also, as (I think) in some of the generated code quoted,
>> use of __builtin_expect() with a boolean expression can
>> force some versions of gcc to generate the integer
>> value of the expression
>
> That's more likely a side effect of the definition of likely/unlikely:
> they expand to !!(x).
>

It seems whether or not using unlikely() inside arch implemented BUG_ON() is arch dependent. Maybe a reasonable method 
to use BUG_ON() is,
1) do not explicitly use unlikely() when using macro BUG_ON().
2) whether or not using unlikely() inside BUG_ON(), it depends on the implementation of BUG_ON(), including arch 
implementation.

So from current feed back, doing "unlikely() optimization" here doesn't make anything better.

Thanks for all of your feed back :-)

-- 
Coly Li
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