Architecture: Power saving in Skylake
It is not a secret that making the processors more efficient is higher up Intel’s priority list than purely increasing their speed. Especially now that CPUs with Core-architecture find their place in tablets with processor TDPs below 5W this is more important than ever.
Intel added two important new technologies to Skylake: Intel Speed Shift Technology and Duty Cycle Control. The latter is primarily of importance for the laptop models, but the former is also found with Skylake-X. Speed Shift Technology is the fancy name for a new technology where the CPU can fully autonomously determine at what performance level it operates. At the moment the operating system is responsible for the choice of the so-called P-states, where the OS indicates if a processor has to operate at full speed (read: maximum (turbo) clock frequency) or if it should operate at a slower speed. The advantage of doing this through the hardware is that the change can be made a lot faster. Intel speaks of an order size of 1 ms via Speed Shift versus an order size of 30 ms using the conventional method through the operating system. On the one hand this means that the processor is on top speed a lot faster when a heavy task is started, which should result in a more responsive system. On the other hand the change back is a lot faster as well, which should have a positive effect on the power consumption.
When Intel announced the SpeedShift technology for the Skylake laptop-processors this was mostly a theoretical story, considering the support in the operating systems was missing. As of today, the support comes with the latest versions of Windows 10.
The Skylake processors also have more power domains, that can be separately configured in terms of voltage. The power gating, or completely turning off a chip electrically, is further improved and can be done with small chip parts. The CPU-cores, the internal communication (of mesh network, more about this on the next page) and the other CPU parts can be regulated separately in terms of frequency with Skylake, which once again should improve the efficiency.