CPU energy save settings

[Tibor Hazafi]

Hi all,

Could somebody please explain for me (like a noob) the 3 common CPU energy save technologies (C-State, C1E, EIST) and their affection by enabling/disabling them to the performance/frequency/voltage/power consumption/heat referring to the desktop and games as well?
My exact goal should be a combination of settings to ensure maximum performance in games (prevent every drops in core clocks/load by power saving), while the CPU doesn't work at full load on the desktop as well.
P.S. I use the "Maximum performance" energy profile in windows (if it counts). I have read this disables EIST. Is it true?

 

[unclewebb]

The Windows High Performance power profile has the minimum processor state set to 100%. This tells the CPU to run at full speed so it does not step up or down in speed. It does not disable EIST (SpeedStep). It just tells the CPU to ignore stepping down its speed when lightly loaded or idle.

Disabling SpeedStep can cause problems because the CPU can get stuck at a lower speed with no way to get back up to full speed. Asus must have been worried about this happening because on some of their boards, the SpeedStep setting in the bios is ignored. Whether SpeedStep is enabled or disabled in the bios, if you check how the CPU is setup, some Asus boards leave SpeedStep enabled to prevent the CPU from getting stuck at a lower speed. As long as the minimum processor state in the Power Options is set correctly, there is no need to disable EIST (SpeedStep).

If you have enabled the deeper C states like C3, C6 and C7, having C1E enabled or disabled will not make any significant difference. The unused CPU cores will be spending the majority of their idle time in one of the lower C states so virtually no time will be spent in C1E. If you are not going to enable C3, C6, C7 then you should enable C1E if you want to reduce heat and power consumption. Best to enable all of them for maximum savings.

Many people recommend that when overclocking that you should disable the C states. I disagree. As long as your overclock is 100% stable, you should be able to have the core C states enabled without it causing any instability. The deep C states will automatically switch CPU cores to 0 MHz and 0 volts when they are not needed. This is the best way to save power and reduce heat.

 

[Tibor Hazafi]

The Windows High Performance power profile has the minimum processor state set to 100%. This tells the CPU to run at full speed so it does not step up or down in speed. It does not disable EIST (SpeedStep). It just tells the CPU to ignore stepping down its speed when lightly loaded or idle.

Disabling SpeedStep can cause problems because the CPU can get stuck at a lower speed with no way to get back up to full speed. Asus must have been worried about this happening because on some of their boards, the SpeedStep setting in the bios is ignored. Whether SpeedStep is enabled or disabled in the bios, if you check how the CPU is setup, some Asus boards leave SpeedStep enabled to prevent the CPU from getting stuck at a lower speed. As long as the minimum processor state in the Power Options is set correctly, there is no need to disable EIST (SpeedStep).

If you have enabled the deeper C states like C3, C6 and C7, having C1E enabled or disabled will not make any significant difference. The unused CPU cores will be spending the majority of their idle time in one of the lower C states so virtually no time will be spent in C1E. If you are not going to enable C3, C6, C7 then you should enable C1E if you want to reduce heat and power consumption. Best to enable all of them for maximum savings.

Many people recommend that when overclocking that you should disable the C states. I disagree. As long as your overclock is 100% stable, you should be able to have the core C states enabled without it causing any instability. The deep C states will automatically switch CPU cores to 0 MHz and 0 volts when they are not needed. This is the best way to save power and reduce heat.

Thank you very much. And have C-States any affect to the performance in games? For example, is it possible, that the CPU switches to a lower state during game, and when it switches back to C0 it causes a visible dip/hiccup?

 

[unclewebb]

CPU cores can go from on of the deep C states into the active C0 state very quickly. Give some games a try with and without the C states enabled. Do you notice any difference? Any dips in performance are usually not C state related.

 

[cucker tarlson]

Thank you very much. And have C-States any affect to the performance in games? For example, is it possible, that the CPU switches to a lower state during game, and when it switches back to C0 it causes a visible dip/hiccup?

that'd be very unusual.

 

[Tibor Hazafi]

CPU cores can go from on of the deep C states into the active C0 state very quickly.

In <this> article on the official Intel site I have read this: "As the C-States get deeper, the exit latency duration becomes longer (the time to transition to C0) and the power savings becomes greater. "
Maybe the longer duration means 0,000000000002ms instead of 0,000000000001ms

 

[Tibor Hazafi]

Disabling SpeedStep can cause problems because the CPU can get stuck at a lower speed with no way to get back up to full speed. Asus must have been worried about this happening because on some of their boards, the SpeedStep setting in the bios is ignored. Whether SpeedStep is enabled or disabled in the bios, if you check how the CPU is setup, some Asus boards leave SpeedStep enabled to prevent the CPU from getting stuck at a lower speed. As long as the minimum processor state in the Power Options is set correctly, there is no need to disable EIST (SpeedStep).

I have an i7-6700K CPU @ 4GHz with 4,2GHz Turbo.
I have set the minimum processor state to 100% by enabling the "High performance" power profile. Most of the time the CPU runs at 4GHz on each core, but monitoring the clocks for 3 hours this was the result according to CPUID HWMonitor:

For some reason each core drops rarily to 800MHz, even if I set EIST to disabled. Why? It should keep the 4GHz all the time, isn't it?

Thanks,
hazazs

 

[unclewebb]

even if I set EIST to disabled

Where did you set EIST to disabled? In the bios? As I already mentioned, some motherboards have a dummy SpeedStep (EIST) setting in the bios that does not actually do anything. You can toggle it on or off and EIST will still be enabled when you boot up into Windows.

I have an i7-6700K CPU @ 4GHz with 4,2GHz Turbo.

If the Minimum processor state is set to 100%, the CPU should be using the full 4.2 GHz all of the time. Intel CPUs are designed to use as much turbo boost as possible.

Edit - If you have your 6700K set up to default specs, it will vary between 4000 and 4200 MHz depending on how many cores are active.

http://www.cpu-world.com/CPUs/Core_i7/Intel-Core%20i7-6700K.html

Many users with Z series boards use the all core turbo feature. In that case, the CPU locks to 4200 MHz.

Do you have any of the C states enabled? Do you know if Windows enabled Speed Shift? This is another control method that Windows 10 can use.

I would recommend that you download ThrottleStop so you can get a better understanding of your CPU.

ThrottleStop 9.6 Download

ThrottleStop is a small application designed to monitor for and correct the three main types of CPU throttling that are being used on many lapto

www.techpowerup.com

It shows C state activity and whether SpeedStep or Speed Shift is enabled or not. It also follows the Intel recommended monitoring procedure for reporting the CPU multiplier. You can turn on the Log File option and it will create a big log file showing exactly what your CPU is doing.

 

[Tibor Hazafi]

Where did you set EIST to disabled? In the bios?

Yeah, but I have set it to enabled since then.

Edit - If you have your 6700K set up to default specs, it will vary between 4000 and 4200 MHz depending on how many cores are active.

It should, but it doesn't. Unless that 799MHz min value in HWMonitor is really fake.

Do you have any of the C states enabled? Do you know if Windows enabled Speed Shift? This is another control method that Windows 10 can use.

These are my settings in the BIOS related to power management (all at default). I don't know Speed Shift, and I still use Windows 7.