linux-kernel - Re: [thisops uV2 04/10] x86: Support for this_cpu_add,sub,dec,inc

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Message-ID: <20101129183333.GA25610@Krystal>
Date:	Mon, 29 Nov 2010 13:33:33 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	akpm@...ux-foundation.org, Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [thisops uV2 04/10] x86: Support for
	this_cpu_add,sub,dec,inc_return

* Christoph Lameter (cl@...ux.com) wrote:
> On Sat, 27 Nov 2010, Mathieu Desnoyers wrote:
> 
> > > +/*
> > > + * Add return operation
> > > + */
> > > +#define percpu_add_return_op(var, val)					\
> > > +({									\
> > > +	typedef typeof(var) pao_T__;					\
> > > +	typeof(var) pfo_ret__ = val;					\
> > > +	if (0) {							\
> > > +		pao_T__ pao_tmp__;					\
> > > +		pao_tmp__ = (val);					\
> > > +		(void)pao_tmp__;					\
> > > +	}								\
> >
> > OK, I'm dumb: why is the above needed ?
> 
> Ensure that the compiler agrees that  *var and val are compatible. Taken
> over from percpu_add_op().

Isn't that the purpose of __builtin_types_compatible_p(t1, t2) ?

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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