Why does Ubuntu slow down when the power supply is turned off?

Question

Dell

Greetings.
I have Ubuntu 14.04 @Dell E5550 (Core i5). There is a significant decrease in performance when the power supply is turned off. For example, passing unit tests of a perl project takes 50 seconds instead of 10.
Disabling energy-saving functions in the BIOS does not solve the problem, and I would not like the percentage to work at maximum all the time.
With the power supply connected and the frequency set to 750MHz (indicator-cpufreq), the tests take 15 seconds.
Without PSU and set frequency to 2.6GHZ (turbo) - 52 sec.
lscpu confirms all frequency settings.
Another feature noted. When booting with the PSU turned off, the maximum CPU frequency can randomly be 1.3GHz, 1.0GHz, and in no way can it be raised to the maximum until you reboot with the power supply turned on.

Answer 1

Most likely, all sorts of stupid services are running (avahi, for example) and along the way all sorts of nonsense is written in /etc/resolv.conf, and for some, the /etc/hosts curve is drawn by all sorts of NetworkMangers.