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SubjectRE: Strange Slowdown
Date
> > > After i switched "High Memory-Support" to "OFF"(4GB
> Before) the speed went
> > > to normal, but now less than half RAM is used.
> > > Any suggestions?
> >
> > This sounds like the top of memory is running uncached due
> to wrong mtrr
> > settings from the BIOS. Can you post your /proc/mtrr
>
> Because of other reasons i'm back to 2.2.19
>
> /proc/mtrr from 2.2.19 show this
> -- /proc/mtrr --
> reg00: base=0x00000000 ( 0MB), size=1024MB: write-back, count=1
> reg01: base=0x40000000 (1024MB), size= 512MB: write-back, count=1
> reg02: base=0x60000000 (1536MB), size= 256MB: write-back, count=1
> reg03: base=0x70000000 (1792MB), size= 128MB: write-back, count=1
> reg04: base=0x78000000 (1920MB), size= 64MB: write-back, count=1
> reg05: base=0x7c000000 (1984MB), size= 32MB: write-back, count=1
> -- end --
> (32MB "missing". Seems like Linux uses these "missing" MBs.)
>
> For the 2.4.X-Kernel i had switched off the MTRR-Kernel-Option!
>
> Maybe i should try it another time with MTRR-Support switched on.
> Or i should use "mem=2016M".
>

I had a similar problem which could be solved by either passing the "mem="
option at boot time as you suggest(in which case you permanently lose the
upper 32MB) or by using the /proc/mtrr interface ( as described in
Documentation/mtrr.txt) to assign the "missing" region. For your system you
might try something like:

echo "base=0x7e000000 size=0x2000000 type=write-back" >| /proc/mtrr

Marvin Justice

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