linux-kernel - Re: [cpuops cmpxchg double V1 2/4] x86: this_cpu_cmpxchg

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Date:	Tue, 14 Dec 2010 16:46:20 -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 V1 2/4] x86: this_cpu_cmpxchg_double()
 support

On 12/14/2010 09:48 AM, Christoph Lameter wrote:
> +
> +/*
> + * Inputs:
> + * %rsi : memory location to compare
> + * %rax : low 64 bits of old value
> + * %rdx : high 64 bits of old value
> + * %rbx : low 64 bits of new value
> + * %rcx : high 64 bits of new value
> + * %al  : Operation successful
> + */
> +ENTRY(cmpxchg16b_cpuops_emu)
> +CFI_STARTPROC
> +
> +#
> +# Emulate 'cmpxchg16b %gs:(%rsi)' except we return the result in
> +# al not via the ZF. Caller will access al to get result.
> +#
> +cmpxchg16b_cpuops_emu:
> +	pushf
> +	cli
> +
> +	cmpq  %gs:(%rsi), %rax
> +	jne not_same
> +	cmpq %gs:8(%rsi), %rdx
> +	jne not_same
> +
> +	movq %rbx,  %gs:(%rsi)
> +	movq %rcx, %gs:8(%rsi)
> +
> +	popf
> +	mov $1, %al
> +	ret
> +
> + not_same:
> +	popf
> +	xor  %al,%al
> +	ret
> +
> +CFI_ENDPROC
> +
> +ENDPROC(cmpxchg16b_cpuops)
> +

NAK on this.  This is acceptable for cmpxchg8b only because we don't
support SMP on 486s anymore.  x86-64 is another matter...
	
	-hpa
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