When using xen-sources-2.6.20-r6, cpu frequency scaling using cpufrequtils breaks, where a stock gentoo-sources-2.6.22-r9 works without problems. Errors that occur are as follows (with scaling not changing processor speed with the Xen kernel): clara src # dmesg | grep powernow powernow-k8: Found 1 AMD Athlon(tm) 64 Processor 3000+ processors (version 2.00.00) powernow-k8: 0 : fid 0xc (2000 MHz), vid 0x2 powernow-k8: 1 : fid 0xa (1800 MHz), vid 0x6 powernow-k8: 2 : fid 0x2 (1000 MHz), vid 0x12 powernow-k8: fid trans failed, fid 0x2, curr 0xc powernow-k8: transition frequency failed powernow-k8: fid trans failed, fid 0x2, curr 0xc powernow-k8: transition frequency failed powernow-k8: fid trans failed, fid 0x2, curr 0xc powernow-k8: transition frequency failed powernow-k8: fid trans failed, fid 0x2, curr 0xc powernow-k8: transition frequency failed powernow-k8: fid trans failed, fid 0x2, curr 0xc powernow-k8: transition frequency failed Reproducible: Always
I'm guessing this is a limitation of the Xen itself and not a kernel bug, and that if frequency scaling would have to be managed by the xen hypervisor rather than linux. I'm not positive about that though. What sort of system are you using both xen and frequency scaling for anyway? Have you tried the 2.6.18 kernel? Sometimes the 2.6.18 kernel works when the 2.6.20 one does not since it is the version released by the upstream xen guys.
It's my home server that's not always doing a huge amount of work. I haven't tried 2.6.18 and it's not a majorly big deal, but it is broken. Maybe a solution is for the xen-sources kernel to remove the scaling configuration options? This would alleviate bugs of this nature. A chat in ##xen on freenode revealed that there are patches out there for the 3.0 series of Xen, but not necessarily for 3.1. It was also noted on a launchpad bug report (Ubuntu) that a fix *may* go into 3.2. I'm not entirely happy with patching what is realistically a perfectly good kernel, but it's certainly worth removing the bits known *not* to work.
As far as I understand the Xen 3.3 patches for 2.6.18 should enable this feature. Please retry with xen-sources-2.6.18-r12 and report back.
