We’ve discussed Speed Shift before in Ian’s Skylake architecture analysis, but despite the in-depth talk from Intel, Speed Shift was noticably absent at the time of the launch of the processors. This is due to one of the requirements for Speed Shift - it requires operating system support to be able to hand over control of the processor performance to the CPU, and Intel had to work with Microsoft in order to get this functionality enabled in Windows 10. As of right now, anyone with a Skylake processor is actually not getting the benefit of the technology, at least right now. A patch will be rolled out in November for Windows 10 which will enable this functionality, but it is worth noting that it will take a while for it to roll out to new Windows 10 purchases.
The processor in question is an Intel Core i7-6600U, with a base frequency of 2.6 GHz, and turbo frequency of 3.4 GHz. Despite the base frequency being rated on the box at 2.6 GHz, the processor can go all the way down to 400 Mhz when idle, so being able to ramp up quickly could make a big impact even on the U-series Skylake processors. My guess is that it will be even more beneficial to the Y series Core m3/m5/m7 parts since they have a larger dynamic range, and typically more thermal constraints.
Speed Shift is just one small part of the overall performance gain, and one that we have not been able to look at until now. It does lead to some pretty big gains in task completion, if the workloads are bursty and short enough for it to make a difference. It can’t increase the absolute performance of the processor, but it can get it to maximum performance in a much shorter amount of time, as well as get it back down to idle quicker. Intel is billing it as improved responsiveness, and it’s pretty clear that they have achieved that.