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

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Message-ID: <20100405204021.GH2525@linux.vnet.ibm.com>
Date:	Mon, 5 Apr 2010 13:40:21 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	Randy Dunlap <randy.dunlap@...cle.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)

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 */
> > 
> > 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.  ;-)

							Thanx, Paul

> OK. I merely followed the coding style of the code added to sched.c by Paul
> McKenney. But you are right, the rest of sched.c does as you say:
> 
> #else /* !CONFIG_SMP */
> 
> #endif /* CONFIG_SMP */
> 
> Will fix.
> 
> Thanks !
> 
> Mathieu
> 
> > 
> > > +
> > >  #ifndef CONFIG_SMP
> > >  
> > >  int rcu_expedited_torture_stats(char *page)
> > 
> > 
> > ---
> > ~Randy
> > 
> 
> -- 
> Mathieu Desnoyers
> Operating System Efficiency R&D Consultant
> EfficiOS Inc.
> http://www.efficios.com
> --
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