From: Denis Efremov <efremov@linux.com>
To: Pavel Machek <pavel@ucw.cz>, Joe Perches <joe@perches.com>
Cc: Michal Marek <michal.lkml@markovi.net>,
Nicolas Palix <nicolas.palix@imag.fr>,
linux-kernel@vger.kernel.org, cocci@systeme.lip6.fr
Subject: Re: [Cocci] [PATCH] scripts: coccinelle: check for !(un)?likely usage
Date: Sun, 1 Sep 2019 20:39:30 +0300 [thread overview]
Message-ID: <45362841-2ae6-e946-2ae0-ab56a98f15ca@linux.com> (raw)
In-Reply-To: <20190901172403.GA1047@bug>
On 01.09.2019 20:24, Pavel Machek wrote:
> Hi!
>
>>> This patch adds coccinelle script for detecting !likely and !unlikely
>>> usage. It's better to use unlikely instead of !likely and vice versa.
>>
>> Please explain _why_ is it better in the changelog.
>>
>> btw: there are relatively few uses like this in the kernel.
>>
>> $ git grep -P '!\s*(?:un)?likely\s*\(' | wc -l
>> 40
>>
>> afaict: It may save 2 bytes of x86/64 object code.
>>
>> For instance:
>>
>> $ diff -urN kernel/tsacct.lst.old kernel/tsacct.lst.new|less
>> --- kernel/tsacct.lst.old 2019-08-25 09:21:39.936570183 -0700
>> +++ kernel/tsacct.lst.new 2019-08-25 09:22:20.774324886 -0700
>> @@ -24,158 +24,153 @@
>> 15: 48 89 fb mov %rdi,%rbx
>> u64 time, delta;
>>
>> - if (!likely(tsk->mm))
>> + if (unlikely(tsk->mm))
>
> Are you sure this is equivalent?
>
> Pavel
Hi,
No, it's not correct. Thanks Rasmus for clarifying the things here.
This was my mistake. As a human, I failed to parse "likely" and "!"
and made too hasty conclusions :)
The correct transformation is in v2. This will be
!likely(tsk->mm) -> unlikely(!tsk->mm)
Thanks,
Denis
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next prev parent reply other threads:[~2019-09-01 17:39 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-25 13:05 [Cocci] [PATCH] scripts: coccinelle: check for !(un)?likely usage Denis Efremov
2019-08-25 15:30 ` Markus Elfring
2019-08-25 21:06 ` Denis Efremov
2019-08-25 15:30 ` Markus Elfring
2019-08-25 16:37 ` Joe Perches
2019-08-25 18:59 ` Denis Efremov
2019-08-25 19:19 ` Julia Lawall
2019-08-28 11:33 ` Rasmus Villemoes
2019-08-28 11:59 ` Joe Perches
2019-08-28 12:33 ` Denis Efremov
2019-08-28 12:33 ` Julia Lawall
2019-08-28 12:41 ` Denis Efremov
2019-08-28 13:57 ` Denis Efremov
2019-08-25 21:19 ` Denis Efremov
[not found] ` <20190901172403.GA1047@bug>
2019-09-01 17:39 ` Denis Efremov [this message]
2019-08-29 17:10 ` [Cocci] [PATCH v2] " Denis Efremov
2019-08-29 17:13 ` Denis Efremov
2019-08-30 0:42 ` Julia Lawall
2019-08-30 6:56 ` Denis Efremov
2019-08-30 8:06 ` Rasmus Villemoes
2019-08-29 20:07 ` Markus Elfring
2019-08-30 7:55 ` Markus Elfring
2019-09-06 20:19 ` Julia Lawall
2019-09-06 20:55 ` Denis Efremov
2019-09-07 8:05 ` [Cocci] [v2] " Markus Elfring
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