What determines whether a core is "active" for Turbo?

[equazcion]

I was recently reading up on how Turbo works with multiple cores, and came across threads like this:

http://www.portvapes.co.uk/?id=Latest-exam-1Z0-876-Dumps&exid=thread...-for-2-cores-or-all-4-cores-on-4790k.2401165/

People seem to be saying the Turbo boost figures depend on how many cores are "active" or "in use", with fewer active cores providing a bigger Turbo boost, and the max boost (Intel's marketing "up to X GHz" figure) only being available when only a single core is "in use."

But what determines whether a core is "active" or "in use"?

When, exactly, in a Windows environment (or any other really), would only a single core ever be active alone? That seems like it would almost never happen, as dozens of background processes are always constantly running from bootup to shutdown. I would think all cores are always "active" albeit at varying loads.

Could someone please explain? Thanks!

 

[pjmssn]

I would be very interested in learning about this as well. I created a thread about my E5-1650V2 for which I have never seen the 3.9 GHz ST turbo boost advertised for this processor.

 

[dullard]

Intel's official answer: https://www.intel.com/content/www/us/en/support/processors/000005641.html
"Operation depends on headroom available in one or more cores. The amount of time the system spends in turbo boost mode depends on workload, environment, and platform design."

I suspect that they keep the exact details proprietary. In a Windows-like environment, all cores will be receiving some activity in almost any normal situation. But, that doesn't mean that the cores are at or near 100% utilization. For example, right now I have about 1800 threads running and my average CPU usage is 1%. Thus, the headroom that each of my cores has is about 99%. Thus, for all intents and purposes, my CPUs are not very much used right now. Intel probably considers none of them to be active.

Edit: It appears that Intel goes off the C-state of cores. Cores in C0 or C1 power management state are considered active. The other states are inactive.

 

[Dufus]

C0 is active, C1 is inactive as it is a halt state whereby the core clock is stopped. For stepped turbo bins though a core c-state C3 (CC3) or higher is required for operation. If 3 cores of a quad core cpu are at CC3 then the other core can run at the highest turbo bin. However in some cases where highest turbo is set across all cores (flat turbo bins) then it becomes moot and any or all cores can run at the highest turbo providing they are running within set thermal and power settings.

While it may appear many tasks are active they may only be active for a few microseconds or milliseconds at a time leaving plenty of time for cores to idle in the deeper C-States. For instance you can check CPU time under the Windows task manager.