[Xen-users] cpufreq=dom0-kernel doesn't work, AMD K8

[Michael Kuron <mkbug@xxxxxxxxxxxxxxxx>]

So I did some more testing and found out that if I run the Dom0 kernel in 
native (non-Xen) mode, I don't even need to inject the fixed DSDT (which, by 
the way, needs to be done without the -e flag from Grub2 to actually take 
effect in the booted OS) since apparently my BIOS provides the _PSS objects 
through the SSDT.

So my next thought was that maybe Xen didn't like the cpufreq stuff being in 
the SSDT instead of the DSDT, so I copied the CPU stuff from the SSDT into my 
custom DSDT. The native kernel worked perfectly fine either way, but in Dom0 
mode I'm still getting the ACPI _PSS errors. However, decompiling 
/proc/acpi/dsdt yields my fixed DSDT and shows very clearly that these objects 
are in fact there!

I also tried adding other related options after cpufreq=dom0-kernel in my Grub2 
Xen config such as dom0_vcpus_pin and cpuidle, but none even showed the 
slightest effect on the output of xm dmesg or the cpufreq errors.

So what I'm thinking now is that the 2.6.32 kernel (at least the one in Debian) 
is having issues with cpufreq=dom0-kernel. Is anybody here who is successfully 
using cpufreq=dom0-kernel on an AMD K8 CPU with Linux 2.6.32 and Xen 4.0.1 who 
has a suggestion on how to get this to work?

On 15.03.2011, at 13:21, mkbug@xxxxxxxxxxxxxxxx wrote:

> I'm running Xen 4.0 on Linux 2.6.32 using the current stock packages provided 
> in Debian Squeeze. The BIOS of this particular computer appears to have a 
> rather bad ACPI implementation and doesn't contain any P-states in the DSDT, 
> so I fixed the DSDT manually and inject it by adding acpi -e /boot/dsdt.aml 
> to my Grub2 configuration.
> 
> This does work perfectly when not booting in Xen mode (cpufreq takes control 
> of the CPU and the CPU fan spins down after half a minute or so). But when I 
> boot in Xen mode, I get these dmesg error messages, suggesting that it 
> ignored the fixed DSDT injected by Grub2 (these are the same errors that 
> showed up in non-Xen mode before I fixed the DSDT):
> [   15.778182] powernow-k8: Found 1 AMD Athlon(tm) 64 X2 Dual Core Processor 
> 4800+ processors (2 cpu cores) (version 2.20.00)
> [   15.778195] [Firmware Bug]: powernow-k8: No compatible ACPI _PSS objects 
> found.
> [   15.778197] [Firmware Bug]: powernow-k8: Try again with latest BIOS.
> 
> I already tried adding cpufreq=dom0-kernel to the Xen line in my Grub 
> configuration, but that didn't do anything either.
> 
> Is there any difference in the way the Linux kernel and Xen access the DSDT? 
> If so, any suggestions on how to get a custom DSDT working with Xen?
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