Date: Wed, 2 Nov 2005 20:42:12 +0300
From: Sergey Vlasov <vsu@altlinux.ru>
To: Ilya <khext@mail.ru>
Cc: linux-kernel@vger.kernel.org
Subject: Re: PAE bug in 2.4?!
Message-Id: <20051102204212.256584e7.vsu@altlinux.ru>
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On Wed, 02 Nov 2005 18:49:55 +0300 Ilya wrote:

> I've ASUS P4P800-Mx-EAYVZ motherboard and have to use a 2GB memory. But
> after including PAE support in kernel it almost twice... Surely, i
> understand, that it's inevitable, the slowing of PAE, but twice?! Does
> anybody faced this problem? Or is there some bug in PAE?! I tested the
> PAE at some other motherboards, but only on this model on asus it works
> strange) 
[skip]
> Here is the difference in kernels:
> khext@al:~$ diff linux-2.4.31/.config linux-2.4.31-PAE/.config
> 61,62c61,62
> < CONFIG_NOHIGHMEM=y
> < # CONFIG_HIGHMEM4G is not set
> ---
> > # CONFIG_NOHIGHMEM is not set
> > CONFIG_HIGHMEM4G=y
> 64c64,65
> < # CONFIG_HIGHMEM is not set
> ---
> > CONFIG_HIGHMEM=y
> > CONFIG_HIGHIO=y

CONFIG_HIGHMEM4G does not enable PAE - it is CONFIG_HIGHMEM64G which
does it.  So the slowdown must be due to something other than PAE.

Please also show the start of dmesg output - lines which look like:

BIOS-provided physical RAM map:
 BIOS-e820: 0000000000000000 - 000000000009fc00 (usable)
 ...
xxxMB HIGHMEM available.
xxxMB LOWMEM available.

Also show the output of "cat /proc/mtrr".  Some systems have buggy MTRR
setup done by BIOS, which can lead to such slowness when using the full
amount of memory.  Such problems may be fixed by a BIOS upgrade, or
worked around by specifying the mem=... option to avoid using the memory
which is not covered by MTTRs (if the amount of such misconfigured
memory is not excessively large).

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