Re: Regression: kernels since 2.6.26 are unusably slow

[Robert Hancock <hancockrwd@gmail.com>]

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