My PC has one Intel Haswell i5 4690, which is supposed to be boosted up to 3.9GHz from the regular frequency 3.5GHz. I do not know if it is possible to use some softwares to turbo boost this cpu on Ubuntu 14.04LTS. THX!
You don't have to do anything; the CPU will do it all by itself in when useful and possible. See Intel Turbo Boost Technology 2.0. Essentially Turbo Boost will temporarily increase the speed of a processor core above the nominal speed if the core is doing work and other cores are not doing much work, if this can be done without going above the rated power consumption for extended periods of time.