linux-kernel - Re: x86_64 ten times slower than i386

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Message-ID: <472D0488.7040404@zytor.com>
Date:	Sat, 03 Nov 2007 16:30:16 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Bo Brantén <bosse@....umu.se>
CC:	linux-kernel@...r.kernel.org, mpm@...enic.com
Subject: Re: x86_64 ten times slower than i386

Bo Brantén wrote:
> On Sat, 3 Nov 2007, Matt Mackall wrote:
> 
>> This is typically due to a problem with the setup of your MTRRs. Try
>> booting with mem=nnnM where nnn is some number smaller than your
>> actual amount of memory.
> 
> Thank you for that advice, the system has 4GB and if I boot with 
> mem=3072M it will run as fast as normal while if I don't use the mem 
> option it will run 10 times slower, however if I use a figure like 
> mem=3500M the kernel will panic, is there any way to determine the 
> highest usable figure without try and error?

Yes, look at how your MTRRs are set up (cat /proc/mtrr).

	-hpa
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