linux-kernel - Re: [PATCH] introduce sys_membarrier(): process-wide memory barrier (v10)

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Date:	Mon, 05 Apr 2010 13:23:55 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, mingo@...e.hu,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Nicholas Miell <nmiell@...cast.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, josh@...htriplett.org,
	dvhltc@...ibm.com, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	Nick Piggin <npiggin@...e.de>,
	Chris Friesen <cfriesen@...tel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] introduce sys_membarrier(): process-wide memory barrier
 (v10)

Paul E. McKenney wrote:
> On Mon, Apr 05, 2010 at 03:10:57PM -0400, Mathieu Desnoyers wrote:
>> * Randy Dunlap (randy.dunlap@...cle.com) wrote:
>>> On Mon, 5 Apr 2010 13:57:37 -0400 Mathieu Desnoyers wrote:
> 
> [ . . . ]
> 
>>>> +#else /* #ifdef CONFIG_SMP */
>>> I don't know that we have a known convention for that, but I would use:
>>>
>>> #else /* not CONFIG_SMP */
>>>
>>> or
>>>
>>> #else /* !CONFIG_SMP */
>>>
>>>> +
>>>> +SYSCALL_DEFINE1(membarrier, unsigned int, flags)
>>>> +{
>>>> +	return 0;
>>>> +}
>>>> +
>>>> +#endif /* #else #ifdef CONFIG_SMP */

or just:

#endif /* #else #ifdef CONFIG_SMP : tell the reader that the #else part of the #ifdef CONFIG_SMP just ended */

ad nauseum.

>>> and:
>>>
>>> #endif /* CONFIG_SMP */
>>>
>>> The "#else #ifdef" is both ugly and too wordy IMO.
> 
> The extra words make it very clear that we are in at the end of the #else
> clause of a #ifdef with the given condition.  With "#endif /* CONFIG_SMP
> */", is the immediately preceding code compiled under CONFIG_SMP or
> !CONFIG_SMP?  You have to dig back and see whether or not there is a
> #else clause.
> 
> But there is no accounting for taste.  ;-)

IYHO.

regards.
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