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

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Message-Id: <200711071038.26263.jesse.barnes@intel.com>
Date:	Wed, 7 Nov 2007 11:38:25 -0700
From:	Jesse Barnes <jesse.barnes@...el.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Ray Lee <ray-lk@...rabbit.org>,
	Bo Brantén <bosse@....umu.se>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: x86_64 ten times slower than i386

On Monday, November 05, 2007 4:26 Andi Kleen wrote:
> On Mon, Nov 05, 2007 at 08:32:24AM -0800, Ray Lee wrote:
> > (Don't trim cc:s.)
> >
> > On Nov 5, 2007 8:00 AM, Bo Brantén <bosse@....umu.se> wrote:
> > >> Intel Core 2 Quad
> > >> and I noticed that the 64-bit versions was at least 10 times
> > >> slower than the 32-bit versions,
> > >
> > > After I uppgraded the BIOS the mtrr looks like below, and now it
> > > works if I boot with mem=4736M so I can use all memory but it
> > > still doesn't work without the mem parameter then it will run as
> > > slow as before.
>
> Then the BIOS is still broken Comapl in to your motherboard vendor.
>
> > > reg00: base=0x00000000 (   0MB), size=2048MB: write-back, count=1
> > > reg01: base=0x80000000 (2048MB), size=1024MB: write-back, count=1
> > > reg02: base=0xc0000000 (3072MB), size= 256MB: write-back, count=1
> > > reg03: base=0xcf800000 (3320MB), size=   8MB: uncachable, count=1
> > > reg04: base=0xcf700000 (3319MB), size=   1MB: uncachable, count=1
> > > reg05: base=0x100000000 (4096MB), size= 512MB: write-back,
> > > count=1 reg06: base=0x120000000 (4608MB), size= 128MB:
> > > write-back, count=1
> >
> > Jesse Barnes (cc:d) wrote a patch to address this, I think (x86:
> > trim memory not covered by WB MTRRs), but as far as I can tell it
> > hasn't been merged yet. System is Intel, 4gb of RAM.
>
> It wasn't merged because it broke booting on some systems.
> Besides the memory would be still lost -- all it did was to automate
> the "mem=XXXX" line.

Andi, do you have any details on which system broke and how?  I haven't 
heard back from you on my last message on the subject... the patch was 
in -mm for awhile with no complaints.

Ultimately, this is a broken BIOS issue, but still, it would be nice if 
the kernel handled it better.

Thanks,
Jesse
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