linux-kernel - Re: [PATCH -v2 6/8] jump_label: Add a new static

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Date:	Tue, 4 Aug 2015 07:51:49 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Jason Baron <jasonbaron0@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <will.deacon@....com>,
	Jiang Liu <liuj97@...il.com>, rabin@....in,
	Ralf Baechle <ralf@...ux-mips.org>,
	David Daney <ddaney@...iumnetworks.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Michael Ellerman <michael@...erman.id.au>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH -v2 6/8] jump_label: Add a new static_key interface

On Tue, Aug 4, 2015 at 7:33 AM, Borislav Petkov <bp@...en8.de> wrote:
> On Tue, Aug 04, 2015 at 08:06:45AM -0400, Steven Rostedt wrote:
>> I just don't like the inconsistency of the initialization and the
>> setting.
>>
>> Either have:
>>
>>  DEFINE_STATIC_KEY_TRUE()
>>  DEFINE_STATIC_KEY_FALSE()
>>
>> and
>>
>>  static_branch_set_true()
>>  static_branch_set_false()
>>
>>
>> or have:
>>
>>  DEFINE_STATIC_KEY_ENABLED()
>>  DEFINE_STATIC_KEY_DISABLED()
>>
>> and
>>
>>  static_branch_enable()
>>  static_branch_disable()
>>
>>
>> But having the DEFINE_STATIC_KEY_TRUE() and static_branch_enable() is
>> confusing, as enable does not mean "make true"!
>>
>> This may seem as bike shedding, but terminology *is* important, and
>> being inconsistent just makes it more probable to have bugs.
>
> I absolutely agree but I read "enable" as enable the branch, so no
> confusion there. Now, it's a whole another question where we branch to.
> And that can be confusing.
>
> Now, let's get back to our example:
>
> +static DEFINE_STATIC_KEY_FALSE(__use_tsc);
>
> We don't use the TSC by default. And that's correct, we need to
> calibrate it first.
>
> After calibration:
>
> +       static_branch_enable(&__use_tsc);
>
> Now here we can get confused: we enable the branch but where we branch
> to? The key name helps here but it is still not quite 100% clear. I'd
> prefer to have:
>
>         static_enable(&__use_tsc);

If everything's consistent about "static_key", then I still like
"static_key_set_true" or "static_key_set".  "static_key_enable" is
okay but not fantastic IMO, and "static_branch_enable" is just
confusing.

--Andy
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