linux-kernel - Re: Re: [PATCH] kernel/module: Use BUG_ON instead of if condition followed by BUG.

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Message-ID: <YHWRyZHkwH3F/Lr2@gunter>
Date:   Tue, 13 Apr 2021 14:42:49 +0200
From:   Jessica Yu <jeyu@...nel.org>
To:     周传高 <zhouchuangao@...o.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH] kernel/module: Use BUG_ON instead of if condition
 followed by BUG.

+++ 周传高 [13/04/21 15:21 +0800]:
>
>>+++ zhouchuangao [30/03/21 05:07 -0700]:
>>>It can be optimized at compile time.
>>>
>>>Signed-off-by: zhouchuangao <zhouchuangao@...o.com>
>>
>>Hi,
>>
>>Could you please provide a more descriptive changelog? I.e., Is this
>>a fix for a cocinelle warning? What are the optimization(s)?
>>
>>Thanks,
>>
>First,
>This patch comes from cocinelle warning.
>
>Second,
>#define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while (0)
>
>BUG_ON uses unlikely in if(). Through disassembly, we can see that
>brk #0x800 is compiled to the end of the function.
>As you can see below:
>    ......
>    ffffff8008660bec:   d65f03c0    ret
>    ffffff8008660bf0:   d4210000    brk #0x800
>
>Usually, the condition in if () is not satisfied. For the multi-stage pipeline,
>we do not need to perform fetch decode and excute operation on brk
>instruction.
>
>In my opinion, this can improve the efficiency of the multi-stage pipeline.

Thanks. Could you please modify your commit/changelog message to
include this information (including the coccinelle warning) and resend
the patch?