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Date: Tue, 9 Jul 2002 05:03:00 +0200
From: Pavel Machek <pavel@ucw.cz>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: John Alvord <jalvo@mbay.net>, Thunder from the hill <thunder@ngforever.de>,
       Pablo Fischer <exilion@yifan.net>, Mark Hahn <hahn@physics.mcmaster.ca>,
       linux-kernel@vger.kernel.org
Subject: Re: StackPages errors (CALLTRACE)
Message-ID: <20020709030259.GA113@elf.ucw.cz>
References: <83ubiu433pkcf41ev9ihl7mgo0tn1kokcc@4ax.com> <E17QaN6-0004Ci-00@the-village.bc.nu>
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Hi!

> > There has also been a patch on L-K which implments CMOV on prior-PPro
> > processors. john
> 
> It has a hideous overhead. Just dont use cmov blindly in kernels. The kernel 
> stuff will take care not to let the compiler stick cmov instructions into
> a non ppro+ kernel

Not only nasty overhead but potential nasty implications. You get
exception where you'd normaly get simple instruction. Do NOT use cmov
emulation for kernel.
									Pavel
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