linux-kernel - Re: General slowness with using 64Gb HIGHMEM option on 32-bit kernel

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Message-Id: <200709281322.44864.nickpiggin@yahoo.com.au>
Date:	Fri, 28 Sep 2007 13:22:44 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	"Sergey Popov" <faijeya@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: General slowness with using 64Gb HIGHMEM option on 32-bit kernel

On Saturday 29 September 2007 03:15, Sergey Popov wrote:
> Short description: after recompiling 32-bit kernel with 64Gb highmem
> support and rebooting into it, OS started working very much slower
> then before.
>
> Specifications: Intel Core 2 Duo E6600@2,4Ghz on Intel i965Q-based
> motherboard. 6Gb of DDR2 RAM, 2x1Gb+2x2Gb, dual-channel.
> Vector Linux 5.8 (Slackware Linux 11-based), 2.6.20.3 kernel.
>
> Long description: after recompiling 32-bit 2.6.20.3 kernel with 64Gb
> highmem option and rebooting into it, booting process froze on udevd.
> After booting up from CD and disabling rc.udev, system started, but
> it's work after rc.M script sarted was 5-10 times slower then usual.
> top showed, that processes are taking much more CPU% time then usual.
> I tried downloading the newest stable kernel - 2.6.22.9 - hoping, that
> it would solve the problem. I downloaded it, booted from CD, and
> compiled it with 64Gb highmem support. I felt some speed improvement,
> but if on 2.6.20.3 machine performed like P166, now it is working like
> P2-350.
> I've found a similar problem, described on lkml -
> http://lkml.org/lkml/2007/5/30/5 . But, unfortunately, it is x86_64
> related and contains no clues for me.

It's most likely the MTRR problem that Rik mentioned.


> Moving to 64-bit distro is rather unpleasant - as there is an option
> in 32-bit kernel, it should work ;) .

If you have a gcc that can compile 64-bit code, then I found it was as
simple as doing a 'make ARCH=x86_64' and building the kernel with 32-bit
program support.
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