Re: [patch 05/61] lock validator: introduce WARN_ON_ONCE(cond)

[Steven Rostedt <rostedt@goodmis.org>]

On Mon, 2006-05-29 at 18:33 -0700, Andrew Morton wrote:
> On Mon, 29 May 2006 23:23:28 +0200
> Ingo Molnar <mingo@elte.hu> wrote:
> 
> > add WARN_ON_ONCE(cond) to print once-per-bootup messages.
> > 
> > Signed-off-by: Ingo Molnar <mingo@elte.hu>
> > Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
> > ---
> >  include/asm-generic/bug.h |   13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > Index: linux/include/asm-generic/bug.h
> > ===================================================================
> > --- linux.orig/include/asm-generic/bug.h
> > +++ linux/include/asm-generic/bug.h
> > @@ -44,4 +44,17 @@
> >  # define WARN_ON_SMP(x)			do { } while (0)
> >  #endif
> >  
> > +#define WARN_ON_ONCE(condition)				\
> > +({							\
> > +	static int __warn_once = 1;			\
> > +	int __ret = 0;					\
> > +							\
> > +	if (unlikely(__warn_once && (condition))) {	\

Since __warn_once is likely to be true, and the condition is likely to
be false, wouldn't it be better to switch this around to:

  if (unlikely((condition) && __warn_once)) {

So the && will fall out before having to check a global variable.

Only after the unlikely condition would the __warn_once be false.

-- Steve

> > +		__warn_once = 0;			\
> > +		WARN_ON(1);				\
> > +		__ret = 1;				\
> > +	}						\
> > +	__ret;						\
> > +})
> > +
> >  #endif
> 
> I'll queue this for mainline inclusion.


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