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 Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1506050 Title: intel cpu frequency is stuck at ~400mhz To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux-lts-vivid/+bug/1506050/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
