linux-kernel - Re: [cpuops cmpxchg double V2 1/4] Generic support for this_cpu_cmpxchg

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Message-ID: <4D263C91.30709@zytor.com>
Date:	Thu, 06 Jan 2011 14:05:05 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	Tejun Heo <tj@...nel.org>, 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 V2 1/4] Generic support for this_cpu_cmpxchg_double

On 01/06/2011 12:45 PM, Christoph Lameter wrote:
> Introduce this_cpu_cmpxchg_double. this_cpu_cmpxchg_double() allows the
> comparision between two consecutive words and replaces them if there is
> a match.
> 
> 	bool this_cpu_cmpxchg_double(pcp1, pcp2,
> 		old_word1, old_word2, new_word1, new_word2)
> 
> this_cpu_cmpxchg_double does not return the old value (difficult since
> there are two words) but a boolean indicating if the operation was
> successful.
> 
> The first percpu variable must be double word aligned!

I really truly hate this interface.  The whole notion of passing two
pointers where only one is really used, is just painful.

	-hpa
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