Usually you’ll want to flash to the newest version of L4T…it arrives with R27.0.1, the update to R27.1 is a significant improvement. Flash on command line requires only an x86_64 PC host with the micro-B USB cable connected. JetPack is a front end to flashing plus it has options for other software you may be interested in…this requires Ubuntu 14.04, although several people have used it with Ubuntu 16.04. In the case of JetPack the USB cable is still used during flash, but wired ethernet is required for the rest of the software. Downloads for command line flash would be the driver package and sample rootfs. When using JetPack (currently version 3.0) it’ll do some downloading for you. See:
Be aware that some of the developer download pages require a login which is a separate login/registration from these forums.
You will end up with something like “/home/ubuntu/jetson_clocks.sh” to be able to view and change performance settings (it’s a human readable file, check out the options).
Much of performance and driver options you are interested in will probably be exposed in the “/sys” directory tree, though it won’t be obvious (the tree is based on driver code, not human readability). You might want to browse “/sys/kernel” for example just to see what is there. You might browse around here: