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To: linux-kernel@vger.kernel.org
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [Q] Looking for an emulation for CMOV* instructions.
Date: 11 Jan 2002 23:52:50 -0800
Organization: Transmeta Corporation, Santa Clara CA
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In-Reply-To: <m26669olcu.fsf@goliath.csn.tu-chemnitz.de.suse.lists.linux.kernel> <E16Oocq-0005tX-00@the-village.bc.nu.suse.lists.linux.kernel> <p737kqpp60w.fsf@oldwotan.suse.de>
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Copyright: Copyright 2002 H. Peter Anvin - All Rights Reserved
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Followup to:  <p737kqpp60w.fsf@oldwotan.suse.de>
By author:    Andi Kleen <ak@suse.de>
In newsgroup: linux.dev.kernel
>  
> One corner case where emulation would IMHO make sense would be CMPXCHG8.
> It would allow to do efficient inline mutexes in pthreads, and hit the
> emulation only on 386/486. cpu feature flag checking is unfortunately
> not an option normally for inline code.
> 

You don't need CMPXCHG8B to do efficient inline mutexes.  In fact, the
pthreads code for i386 uses the same mutexes the kernel does (LOCK INC
based, I believe), complete with section hacking to make them
efficiently inlinable -- and then they're put inside a function call.
I believe "kill me now" is an appropriate response.

	-hpa

-- 
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."
http://www.zytor.com/~hpa/puzzle.txt	<amsp@zytor.com>
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