13 Replies Latest reply on May 17, 2016 12:53 PM by DiegoV_Intel

    CPU Power management on Yocto (edison-image) C-states


      Hi everyone,


      I'm trying to manage the power of the Edison Atom CPU. I have never done that before, but I have read that it's possible to reduce the clock of a CPU via /sys/devices/cpu/... .

      I have also read that each processor can be switched to differents performance states (P-states) or power saving states (C-states). Here I think I have understood that every processor can be switched from C0 (full performance, max clock frequency) to C3 (power saving, low clock frequency). On some specific CPU we can set the power state down to C10.

      I have found that the Atom processor of the Edison can be set to C6 (or C7 I'm not sure).


      However, I can't find a way to manage those modes via the linux fs of the official yocto image.


      I am also a little confused about how the C-states are related to clock frequencies. Do C-states only shut down some parts in the cpu? And reducing the clocks frequencies correspond only to reducing voltage in the circuit? I mean, in C6 mode we can't reduce clock's frequency because they are off right?



      So my questions are: How to manage power in user space ? How to switch cpu in different C-modes?

      Could you confirm or not what I am saying?


      Thank you in advance.


      Pierre Collet