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Message-ID: <440E9B41.9020708@yahoo.com.au>
Date: Wed, 08 Mar 2006 19:52:17 +1100
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Andrew Morton <akpm@osdl.org>
CC: Benjamin LaHaise <bcrl@kvack.org>, mingo@elte.hu,
       76306.1226@compuserve.com, linux-kernel@vger.kernel.org,
       torvalds@osdl.org
Subject: Re: [patch] i386 spinlocks: disable interrupts only if we enabled
 them
References: <200603071837_MC3-1-BA13-E5FB@compuserve.com>	<20060307161550.27941df5.akpm@osdl.org>	<20060308004308.GA16069@elte.hu>	<20060308025227.GP5410@kvack.org> <20060307225556.75cee661.akpm@osdl.org>
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Andrew Morton wrote:
> Benjamin LaHaise <bcrl@kvack.org> wrote:
> 
>>On Wed, Mar 08, 2006 at 01:43:08AM +0100, Ingo Molnar wrote:
>> > we dont inline that code anymore. So i think the optimization is fine.
>>
>> Why is that?  It adds memory traffic that has to be synchronized 
>> before the lock occurs and clobbered registers now in the caller.
> 
> 
> Is the inlined lock;decb+jns likely to worsen the text size?  I doubt it. 
> Overall text will get bigger due to the out-of-line stuff, but that's OK.
> 
> I'm sure we went over all this, but I don't recall the thinking.

Seems like a very good idea not to clobber any registers in
lock fastpaths. I don't see how that could have been a win
(especially for i386) but still, Ingo must have had a reason
behind it.

-- 
SUSE Labs, Novell Inc.
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