Turns out that this was because I had a 'new' version of the intel microcode that I must have downloaded from Intel itself in /lib/firmware /intel-ucode when trying to diagnose a VM lockup a year or so ago. It updated my Haswell to 0x29, whether it's the upgrading of the microcode or the 0x29 microcode itself causing the problem I'm not sure.
Using the 'vanilla' intel-microcode package without any modifications seems to work fine. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux-lts-vivid in Ubuntu. https://bugs.launchpad.net/bugs/1506050 Title: intel cpu frequency is stuck at ~400mhz Status in linux-lts-vivid package in Ubuntu: New Bug description: I upgraded an install of 14.0.4.3 to the LST Enablement Stack for Vivid (kernel 3.19) that is running on a Xeon E5-1630 V3 (a Haswell Quad-Core) . Booting with 3.19 would result in the system being very sluggish. 'cpupower frequency-info' would report that the CPU was running at around 400mhz, as would 'cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq'. The CPUs would remain around 400mhz regardless of load. This was using the intel_pstate driver and the powersave governor. Switching to the performance governor had no effect. Using the acpi- cpufreq driver also had no effect, the system was still sluggish even though the reported frequencies in /sys/devices/. Eventually I tracked it down to the original install having had the intel_microcode package installed at some point. Once I removed this then the CPU frequencies scaled correctly with load. FYI the particular version installed was intel-microcode/trusty-updates,now 2.20140624-t-1ubuntu2 amd64. ProblemType: Bug DistroRelease: Ubuntu 14.04 Package: linux-image-3.19.0-30-generic 3.19.0-30.34~14.04.1 ProcVersionSignature: Ubuntu 3.19.0-30.34~14.04.1-generic 3.19.8-ckt6 Uname: Linux 3.19.0-30-generic x86_64 NonfreeKernelModules: nvidia zfs zunicode zcommon znvpair zavl ApportVersion: 2.14.1-0ubuntu3.15 Architecture: amd64 Date: Wed Oct 14 12:38:05 2015 InstallationDate: Installed on 2014-08-05 (434 days ago) InstallationMedia: Lubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140416.2) SourcePackage: linux-lts-vivid UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux-lts-vivid/+bug/1506050/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp