linux-kernel - Re: [cpuops cmpxchg double V1 1/4] Generic support for this_cpu_cmpxchg

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Date:	Mon, 3 Jan 2011 16:43:26 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Tejun Heo <tj@...nel.org>
cc:	"H. Peter Anvin" <hpa@...or.com>, akpm@...ux-foundation.org,
	Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [cpuops cmpxchg double V1 1/4] Generic support for
 this_cpu_cmpxchg_double

On Mon, 27 Dec 2010, Tejun Heo wrote:

> On Sat, Dec 25, 2010 at 05:55:22PM -0600, Christoph Lameter wrote:
> > On Sat, 25 Dec 2010, Tejun Heo wrote:
> >
> > > ABI.  But that said, it might still be problematic on other
> > > architectures when we try to apply it to different architectures.  Is
> > > everyone against just taking a scalar for the first variable instead
> > > of taking a pointer?  I'd be happier with that than the current one.
> >
> > How about replacing that with two scalars? Macro will check that the
> > scalaers are properly aligned and that the second follows the first. Then
> > there is also better symmetry in the parameters.
> >
> > bool this_cpu_cmpxchg_double(
> >           percpu_1, percpu_2
> >           old_1, old_2
> >           new_1, new_2
> > )
>
> Yeah, maybe.  The interface is a bit redundant but probably the most
> fool proof.  I'm okay with either taking a single scalar or both.

The single large 128 bit scalar does not work. Having to define an
additional structure it also a bit clumsy. I think its best to get another
patchset out that also duplicates the first parameter and makes the percpu
variable specs conform to the other this_cpu ops.

Still on vacation so it may take to the end of the week for me to get this
done.

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