IPG for Linux

[gmierz]

On Linux (Ubuntu 18.04), installing IPG from the link provided doesn't work and I had to make some modifications to get it to run on the 8th generation Intel processor - other generations (after SandyBridge) will probably need the same modification which is to add the processor signature to the supported list. I added 0x806e0 (Intel i7 8th generation) here: https://github.com/gmierz/intel-power-gadget/blob/master/rapl.c#L257

I've created a repo with the updated tool that you could link to in your README: https://github.com/gmierz/intel-power-gadget