linux-kernel - Re: [tip:core/locking] locking, x86: Slightly shorten __ticket_spin

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Date:	Wed, 02 Dec 2009 14:59:42 +0000
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"Avi Kivity" <avi@...hat.com>
Cc:	<a.p.zijlstra@...llo.nl>, "Ingo Molnar" <mingo@...e.hu>,
	<tglx@...utronix.de>, <torvalds@...ux-foundation.org>,
	<mingo@...hat.com>, <npiggin@...e.de>,
	<linux-kernel@...r.kernel.org>,
	<linux-tip-commits@...r.kernel.org>, <hpa@...or.com>
Subject: Re: [tip:core/locking] locking, x86: Slightly shorten	
	 __ticket_spin_trylock()

>>> Avi Kivity <avi@...hat.com> 02.12.09 15:36 >>>
>On 12/02/2009 04:25 PM, Jan Beulich wrote:
>>>>> Avi Kivity<avi@...hat.com>  02.12.09 15:12>>>
>>>>>          
>>> Wouldn't 'u8 ret', as an additional argument be sufficient? gcc still
>>> ought to be able to use the same register for new and ret if we remove
>>> the early clobber.
>>>      
>> We can't (validly) remove the early-clobber, otherwise the compiler
>> would be permitted to use a register also used for addressing the lock
>> structure for "new".
>>    
>
>I meant for 'ret'.

But unless you drop the early-clobber on new, the compiler will have
to allocate another register, which I think is not desirable here.

Jan

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