Ubuntu is very slow when Intel SpeedStep is enabled (CPU is not used in full speed)

Solution 1:

This answer applies to the newly discovered reason of the BIOS limiting the CPU frequency.

Please check the condition of your power adapter and your battery. Are they functioning normally? Is the battery charging normally? Does the Laptop work O.K. on battery only?

Typically, Dell bios forces low CPU frequency when something is wrong with the power and / or it no longer recognizes the power adapter.

There is a way to by-pass the inclusion of the /sys/devices/system/cpu/cpu*/cpufreq/bios_limit, but it should only be done as a very last resort and with clear knowledge that the lowest level protection is being disabled. So let's not go there yet.

Solution 2:

For CPU clock frequency governing 14.04 used the acpi-cpufreq driver by default and 14.10 uses intel_pstate driver by default. There are reports of issues similar what you are experiencing.

As a test, please try switching back to the acpi-cpufreq driver. Save a copy of your /etc/default/grub file, just in case:

sudo cp /etc/default/grub /etc/default/grub.original

Edit, as sudo, your /etc/default/grub file and add this parameter to the GRUB_CMDLINE_LINUX_DEFAULT line:

GRUB_CMDLINE_LINUX_DEFAULT="intel_pstate=disable"

If there are already other parameters on that line, then add the new one. Example:

GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1 intel_pstate=disable crashkernel=384M-:128M"

After you save the file, then update grub:

sudo update-grub

Re-boot the computer.

You could also check if you have thermald running:

sudo service thermald status

And if yes, and just for a quick test, disable it (Note you should monitor temperatures when thermald is disabled):

sudo service thermald stop

If you then get some ability for the CPU frequency to increase under significant load, then something is likely wrong with your /etc/thermald/thermal-conf.xml file.