Re: Regression: kernels since 2.6.26 are unusably slow

From: Robert Hancock
Date: Fri Sep 25 2009 - 22:49:22 EST


On 09/25/2009 07:47 PM, Yinghai Lu wrote:
On Fri, Sep 25, 2009 at 6:02 PM, Aneurin Price<aneurin.price@xxxxxxxxx> wrote:

Hmm. Looking at dmesg for a 'working' kernel includes an interesting part which
I foolishly forgot to save, saying that the last 512MB of memory is
inaccessible (I was wondering where that last half-gig had gone :-)). I can go
and check exactly what it says, but I don't have the energy left for any more
reboots today. Anyway, that prompted me to try booting with mem=7168 - and that
makes the problem go away. Perhaps that will shed some light on things.

[ 0.000000] BIOS-e820: 0000000000000000 - 000000000009e800 (usable)
[ 0.000000] BIOS-e820: 000000000009f800 - 00000000000a0000 (reserved)
[ 0.000000] BIOS-e820: 00000000000f0000 - 0000000000100000 (reserved)
[ 0.000000] BIOS-e820: 0000000000100000 - 00000000dfee0000 (usable)
[ 0.000000] BIOS-e820: 00000000dfee0000 - 00000000dfee3000 (ACPI NVS)
[ 0.000000] BIOS-e820: 00000000dfee3000 - 00000000dfef0000 (ACPI data)
[ 0.000000] BIOS-e820: 00000000dfef0000 - 00000000dff00000 (reserved)
[ 0.000000] BIOS-e820: 00000000f0000000 - 00000000f4000000 (reserved)
[ 0.000000] BIOS-e820: 00000000fec00000 - 0000000100000000 (reserved)
[ 0.000000] BIOS-e820: 0000000100000000 - 0000000220000000 (usable)
[ 0.000000] DMI 2.4 present.
[ 0.000000] last_pfn = 0x220000 max_arch_pfn = 0x400000000
[ 0.000000] MTRR default type: uncachable
[ 0.000000] MTRR fixed ranges enabled:
[ 0.000000] 00000-9FFFF write-back
[ 0.000000] A0000-BFFFF uncachable
[ 0.000000] C0000-CDFFF write-protect
[ 0.000000] CE000-EFFFF uncachable
[ 0.000000] F0000-FFFFF write-through
[ 0.000000] MTRR variable ranges enabled:
[ 0.000000] 0 base 100000000 mask FE0000000 write-back
[ 0.000000] 1 base 100000000 mask F00000000 write-back
[ 0.000000] 2 base 000000000 mask F00000000 write-back
[ 0.000000] 3 base 0E0000000 mask FE0000000 uncachable
[ 0.000000] 4 base 0DFF00000 mask FFFF00000 write-through
[ 0.000000] 5 disabled
[ 0.000000] 6 disabled
[ 0.000000] 7 disabled

looks like your MTRR has some problem, and with that WRITE-THROUGH
there, the trimming e820 will not happen

You might want to see if there's a BIOS update available for that system/motherboard..
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