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

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Message-ID: <4D081225.8000007@zytor.com>
Date:	Tue, 14 Dec 2010 16:56:05 -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 V1 2/4] x86: this_cpu_cmpxchg_double()
 support

On 12/14/2010 04:46 PM, H. Peter Anvin wrote:
> 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.
>> +#
> 
> NAK on this.  This is acceptable for cmpxchg8b only because we don't
> support SMP on 486s anymore.  x86-64 is another matter...
> 	

Hm, this is meant to be a CPU local operation, isn't it... it isn't very
clear from the comments or naming *in this file*.

Could you make it a little clearer in the local code, please?

	-hpa
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