Dear all, as it turns out, the issue has nothing to do with secure boot:
no matter whether secure boot is enabled or disabled, if the CPU frequency hits the 400MHz min. threshold it gets stuck at that value. When the CPU frequency hits the 400MHz min. threshold is hard to say, but it seems to only happen when the laptop is on battery power. The only reliable way to recover from a situation in which the CPU frequency is stuck at 400MHz seems to be to connect the computer to the AC power. It is perhaps useful to add that setting the min. CPU frequency to 900MHz > /usr/bin/cpupower -c all frequency-set -g powersave > /usr/bin/cpupower -c all frequency-set -d 900MHz is effective > nicola@loki:~$ sudo cpupower frequency-info > analyzing CPU 0: > driver: intel_pstate > CPUs which run at the same hardware frequency: 0 > CPUs which need to have their frequency coordinated by software: 0 > maximum transition latency: Cannot determine or is not supported. > hardware limits: 400 MHz - 3.50 GHz > available cpufreq governors: performance powersave > current policy: frequency should be within 800 MHz and 3.50 GHz. > The governor "powersave" may decide which speed to use > within this range. > current CPU frequency: Unable to call hardware > current CPU frequency: 900 MHz (asserted by call to kernel) > boost state support: > Supported: yes > Active: yes but does not prevent the CPU frequency to occasionally get stuck to 400MHz on battery power. Best, Nicola
