March 11, 2020

Permanently change maximum CPU frequency of X61 back to 2.4GHz

I had a weird issue where the CPU frequency of my Thinkpad X61 was stuck at half the clock speed, i.e. 1.2GHz. Manual override using the cpufreq-set tool did not work. After some investigation it turned out, that the reason was falsly reported limit form the bios in the file:

/sys/devices/system/cpu/cpu0/cpufreq/bios_limit

Thanks to this post on ask-ubuntu (https://askubuntu.com/questions/340626/permanently-change-maximum-cpu-frequency) i could resolve the issue with a kernel boot parameter:

GRUB_CMDLINE_LINUX_DEFAULT=" ... processor.ignore_ppc=1"

I benchmarked the CPU with:

sysbench cpu --threads=2 run

Before the fix the Intel Core2Duo T8300 returned ~880 events/s. After the fix that number increased to 1800 events/s. That is a whopping 200% – as expected after doubling the frequency from 1.2GHz to 2.4GHz. Sideremark – my current daily driver, a Macbook pro with Intel I7-8559U has 7500 events/s :)