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

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Message-ID: <alpine.DEB.2.00.1101211121350.15692@router.home>
Date:	Fri, 21 Jan 2011 11:24:47 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	Tejun Heo <tj@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [cpuops cmpxchg double V2 1/4] Generic support for
 this_cpu_cmpxchg_double

On Fri, 21 Jan 2011, H. Peter Anvin wrote:

> We could do cmpxchg with a structure... the problem with a lon int type is that Cristoph ran into bugs with __int128 on 64 bits.

We also would need to be pass the structure by value (well its really a
variable but its like passing by value) in order to be similar to the
other this_cpu_ops

You'd want either

DEFINE_PERCPU(struct mycustomdoublestruct, percpu_dd)

this_cpu_cmpxchg_double(percpu_dd, oldword1, oldword2, newword1, newword2)

with the problem of type checking

or

this_cpu_cmpxchg_double(percpu_dd, old_dd, new_dd)

with the problem of 128 bit constants/structs passed by value.




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