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Message-ID: <4D0CC982.3030905@kernel.org>
Date: Sat, 18 Dec 2010 15:47:30 +0100
From: Tejun Heo <tj@kernel.org>
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To: Christoph Lameter <cl@linux.com>
CC: akpm@linux-foundation.org, Pekka Enberg <penberg@cs.helsinki.fi>,
        linux-kernel@vger.kernel.org, Eric Dumazet <eric.dumazet@gmail.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Subject: Re: [cpuops cmpxchg double V1 1/4] Generic support for this_cpu_cmpxchg_double
References: <20101214174847.887713690@linux.com> <20101214174900.058235985@linux.com>
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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