Kernel upgrade 2.4 -> 2.6, makes system very slow on laptop with 1GB of memory: BIOS caching bug
- From: Mark.Sandler@xxxxxxxxx
- Date: 26 Feb 2006 19:06:14 -0800
Hi,
I thought I should post the problem and solution here as it seems to be
very evasive bug (and took me days to solve), hopefully someone will
find it useful (and lemme know if it did ;)
The problem:
After upgrading (or installing fresh ) to 2.6.x kernel on
Debian/Ubuntu Linux system, the computer has became very slow. And i
mean REALLY slow -- it was taking 50 minutes just to boot.
Reason
Apparently the problem is that there is a bug in BIOS (quite popular),
which prevents memory region from 1008 to 1016 from being cached, and
linux is using that memory region quite actively. To check if this is
indeed the case try
cat /proc/mtrr
at the end where it displays caching region there will be a gap
somewhere in the high memory. (look for numbers starting with 0x3E and
3F)
Solution:
mem=1008M added to kernel options e.g. if one uses grub the
/usr/menu.lst
should read like:
kernel /boot/vmlinuz-2.6.12custom root=/dev/hda3 ro mem=1008M
single
Now, everything works just fine. But in my case sound, pcmcia and few
other things including
acpi stopped working.
Iteration 2.
Detailed study of the output of lspci command (use verbose option)
tells us that sound card uses memory region from 1016 to 1024MB...
Apparently when one specifies mem=1008M, kernel can not access that
region and <sigh> no sound...
The "hackish" solution is to turn off the the mem_4G option in the
kernel. For that one needs to recompile kernel with Mem4G option turned
off... Note, that in that case some top 100M will be inaccessible for
programs - but i guess it doesn't really matter. Interestingly enough,
the sound card still continues to use 1016-1024M region, and so once
one recompiles the kernel, s/he _has_ to remove the offending mem=1008
from the menu.lst....
I guess alternative would be to try to reconfigure sound not to use the
region above 1008 --
but i have not tried that.
Side note (and off topic).
The similar problem can be seen in Windows XP... (But of course one
would have no chance of finding out the cause for it, except by
installing linux...), the problem is even more evasive. The windows
would get very slow, not all the time, but only when some program
loads into uncached region... Eg. every few days or so...
The solution: add /maxmem=999 option to c:\boot.ini file.
enjoy,
mark
.
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