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

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Date:	Sat, 18 Dec 2010 15:47:30 +0100
From:	Tejun Heo <tj@...nel.org>
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>,
	"H. Peter Anvin" <hpa@...or.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [cpuops cmpxchg double V1 1/4] Generic support for this_cpu_cmpxchg_double

Hello, Christoph.

On 12/14/2010 06:48 PM, Christoph Lameter wrote:
> +/*
> + * cmpxchg_double replaces two adjacent scalars at once. The first parameter
> + * passed is a percpu pointer, not a scalar like the other this_cpu
> + * operations. This is so because the function operates on two scalars
> + * (must be of same size). A truth value is returned to indicate success or
> + * failure (since a double register result is difficult to handle).
> + * There is very limited hardware support for these operations. So only certain
> + * sizes may work.
> + */
> +#define __this_cpu_generic_cmpxchg_double(pcp, oval1, oval2, nval1, nval2)	

This is ugly. :-( I think we should have made this_cpu_*() ops take
pointers from the beginning.  Anyways, that's too late, so is it
completely impossible to make cmpxchg_double's take a scalar value?
It can take the pointer all the same, no?

Thanks.

-- 
tejun
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