linux-kernel - Re: [thiscpuops upgrade 09/10] x86: this_cpu_cmpxchg and this_cpu_cmpxchg

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Date:	Wed, 24 Nov 2010 01:41:41 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	akpm@...ux-foundation.org, Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [thiscpuops upgrade 09/10] x86: this_cpu_cmpxchg and
 this_cpu_cmpxchg_double operations

Le mardi 23 novembre 2010 à 17:51 -0600, Christoph Lameter a écrit :
> pièce jointe document texte brut (this_cpu_cmpxchg_x86)
> Provide support as far as the hardware capabilities of the x86 cpus
> allow.
> 
> Signed-off-by: Christoph Lameter <cl@...ux.com>

> +
> +#define percpu_cmpxchg16b(pcp, o1, o2, n1, n2)				\
> +({									\
> +	char __ret;							\
> +	typeof(o1) __o1 = o1;						\
> +	typeof(o1) __n1 = n1;						\
> +	typeof(o2) __o2 = o2;						\
> +	typeof(o2) __n2 = n2;						\
> +	asm("cmpxchg16b "__percpu_arg(1)"\n\tsetz %0\n\t"		\
> +		    : "=a"(__ret), "=m" (*pcp)				\
> +		    :  "b"(__n1), "c"(__n2), "a"(__o1), "d"(__o2));	\
> +	__ret;								\
> +})

I thought some x86_64 cpus dont have cmpxchg16b ?

You have to check cx16 feature flag or implement a fallback ?




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