Surface pro 4 - clock speed of CPU keeps the same

Actually, the culprit seems to be Microsoft using 0 as default value for "Processor energy performance preference policy". This tells your Speed Shift enabled Skylake CPU not to sacrifice performance for energy savings under any circumstances resulting in a permanent max turbo state. You can now either go back to the old supposedly inferior OS controlled P-states and disable Speed Shift by setting "Processor performance autonomous mode" to disabled

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Power\PowerSettings\54533251-82be-4824-96c1-47b60b740d00\8baa4a8a-14c6-4451-8e8b-14bdbd197537]

"Attributes"=dword:00000002

or let Speed Shift actually do its job by giving it a useful policy to work with

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Power\PowerSettings\54533251-82be-4824-96c1-47b60b740d00\36687f9e-e3a5-4dbf-b1dc-15eb381c6863]

"Attributes"=dword:00000002

If you set "Processor energy performance preference policy" to 50, you will see Speed Shift happily using anything from 0.5 GHz up to the max turbo frequency. By the way, 100 results in your CPU rarely exceeding 1.0 GHz.

The current default settings most likely just disable DVFS while still allowing cores to sleep in C7, which could explain battery life being similar in a light use scenario.

Happy to help.

After the AU I had to fix a lot of issues. But as for the processor speed, I think your test shows we'll be fine just waiting for a fix. For now, anyway.

I'm getting ~5 hrs after the fix, kind of worse than before (~6 under similar workload?).

Besides I found the frequency control policy much more conservative. It could stay > 2 GHz for 10 minutes when idle (not a strong evidence though).

 I've been looking into this, and here's what I found out:

 There is a technology called "Intel Speed Shift". In a computer, the OS tells the processor to speed up or slow down depending on current needs. Intel Speed Shift turns control of that over to the processor, and as a result everything is quicker (and theoretically can save a small amount of battery life).

 Intel Speed Shift came out in November of last year, but is only now being "turned on" by Windows. "Processor Performance Autonomous Mode" is the on / off switch for Intel Speed Shift.

THEORY:

 One of two things is probably happening on our Surface devices.

1. Intel Speed Shift is causing the OS to report an incorrect processor speed. Since many CPU diagnostic programs read the speed from the OS, they are also misreporting it. This may be supported by the fact our fans are not running constantly and battery life is nearly the same as it was before the update.

OR

2. Intel Speed Shift, or it's connection with Windows, is flawed and causes our CPUs to run too fast.

 Therefore, if you apply one of the registry fixes you are merely turning off Intel Speed Shift. This turns control of the CPU back over to Windows and things run as before. Alternately, you can leave it on and wait for a patch to allow Intel Speed Shift and Windows to work together properly.

Personally, since I'm not noticing dramatic heat or battery use increases, I'm waiting a bit to see how MS may update the integration of Intel Speed Shift.

For fun - here are some of the new Win 10 power processor settings:

8baa4a8a-14c6-4451-8e8b-14bdbd197537 – Processor performance autonomous mode (Enable/Disable)

Specify whether processors should autonomously determine their target performance state.

36687f9e-e3a5-4dbf-b1dc-15eb381c6863 – Processor energy performance preference policy (Percent)

Specify how much processors should favor energy savings over performance when operating in autonomous mode.

cfeda3d0-7697-4566-a922-a9086cd49dfa – Processor autonomous activity window (Microseconds)

Specify the time period over which to observe processor utilization when operating in autonomous mode.

4e4450b3-6179-4e91-b8f1-5bb9938f81a1 – Processor duty cycling

Specify whether the processor may use duty cycling

More fun if you're a tech person: http://www.anandtech.com/show/9582/intel-skylake-mobile-desktop-launch-architecture-analysis/7

Thanks for the information...that makes a lot of sense.   I just did a small test on my SP4 to check your theories.  With Processor Performance Autonomous Mode enabled (Default Setting) I let the SP4 run for 1 hour.  The system was largely sitting idle, connected to WiFi with several application open.  The CPU was reporting 2.19GHz the entire time.  The system was cool the whole time and the fans did not kick on at all.  During the hour, the battery dropped 12%.

Then, I used the registry settings to disable Processor Performance Autonomous Mode and let it run for another hour with the same apps running.  The system was again largely idle but the processor stayed under 1GHz pretty much the entire time the entire time.  The system was cool the whole time and the fans did not kick on at all.  Under this scenario, the battery actually dropped 13%.  You would think that with the much lower clock speed, the battery drain would be less...but it was actually more.

Of course this was not a scientific test by any means, but it certainly would point to your theory #1 being correct and that the processor is still throttling correctly by using Processor Performance Autonomous Mode, just not reporting correctly to the OS.