Need help understanding Volts vs Watts re: OC power efficiency

[frenchy70]

I have been overclocking an i5 750 on a Gigabyte GA-P55M-UD2 board, at 3.6 Ghz, going up to 4.1 Ghz with Turbo for 1 - 2 cores.

I want to understand the difference between voltage and watts when I use a fixed voltage vs an offset voltage.

Is it a problem to have a constant CPU voltage of 1.325v, when the watts are going up and down with ALL of the power savings features on ?

Or is it preferable to have CPU voltage changing all the time, so we have low voltage around 0.9v when idle and up to 1.325v only when under load ?

I'm asking because, it seems that I might prefer to use static voltage settings instead of offset because I seem to have some instability problems with offset changing the voltages all over the place (thought I'd fixed it but haven't totally).

With a fixed voltage, my volts are obviously always the same as displayed in CPU-Z or CPUID Hardware Monitor - say around 1.325v. but of course, I can see the Watts reading change from 14w lowest when idle up to about 110w under full-load during stress testing.

With an offset voltage, my voltage is between 0.9v and 1.325v.

So, IF I wanted to run with fixed voltage, am I really consuming much more power than if I had offset voltage because it seems to me that the watts are going way down because the power saving measures are doing their job properly ?

Same question with regards to processor wear - if the CPU isn't loaded much, does it matter that volts are static at 1.325v all the time ?

 

[Bejusek]

You are right. Offset CPU voltage is preferable.
Simply because the PC is idling most of the time, lower VCore means lower power consumption.
Power consumption rises linearly with CPU clock. If multiplier and voltage are decreased when PC is idle, you have two factors that decrease CPU power consumption. Setting Vcore to constant leaves you with only one of them. There is also a third factor - temperature. Higher temperature means higher power consumption. So even when multiplier is lowered and Vcore is const. there is more heat and power draw has to be higher.
The ability to change VCore depending on load is the most important power saving feature there is.

Lower voltage means lower stress on CPU components and increases its lifespan. However, running a constant voltage similar to normal max. voltage CPU uses (or for example increased some 0.05V) shouldn't have much impact on its longevity. It's hard to estimate, but I believe that with constant voltage this processor will last much longer than it will be used.

By the way, how are you measuring watts? If it is CoreTemp reading, then it shouldn't be relied upon.

 

[frenchy70]

Thanks for your response.

Yes - I understand what you are saying BUT what I was getting at is, does it matter so much if the voltage is fixed at 1.3 or whatever because when the computer is idle, the processor is throttled back on 4 cores, the load is low, the temps are really low (like 28°C).

And I'm reading watts from CPUID Hardware Monitor. I appreciate that it might not be an accurate reading, but surely if Hardware Monitor says that my CPU is drawing 110w at full load overclocked to 4 Ghz, and then it shows the CPU drawing 10w when the processor is idle (at about 1.5 Ghz), then surely the DIFFERENCE between the two figures is reasonably accurate ?? No ?

So I'm asking:

Am I correct that I'm not spending MUCH more money on electricity than I would like - because with C-states, EIST, Windows Power Saving profile, all enabled, the watts are low when the computer is being worked hard ?? It seems that is the case, even if the voltage is set at a constant 1.325v.

I assume I am right because the reason the temperatures rise when stress testing, the CPU is working hard, drawing a lot more power and therefore getting hot.

If I am correct about not wasting too much energy, then I would like to know, "Am I wearing the CPU more than "reasonable" if I leave CPU voltage at a constant 1.325v, if it is mostly at idle while not playing games" ??

I don't have a clue about how "high" constant voltage affects the life of the CPU if it isn't being loaded with constant high workload much - maybe its better for it than having the volts changing all the time (wishful thinking).

Thanks for any more thoughts.

 

[Bejusek]

Yes - I understand what you are saying BUT what I was getting at is, does it matter so much if the voltage is fixed at 1.3 or whatever because when the computer is idle, the processor is throttled back on 4 cores, the load is low, the temps are really low (like 28°C).

And I'm reading watts from CPUID Hardware Monitor. I appreciate that it might not be an accurate reading, but surely if Hardware Monitor says that my CPU is drawing 110w at full load overclocked to 4 GHz, and then it shows the CPU drawing 10w when the processor is idle (at about 1.5 Ghz), then surely the DIFFERENCE between the two figures is reasonably accurate ?? No ?

I tried to point that when using constant voltage, even in idle, your power draw will be higher. It probably is marginally higher, but still is. Same with temperature.
Software-measured power consumption almost always is a rough estimation. The only way to confirm how accurate it is, is to use a wattmeter.
Difference between the readings on load and idle should be more or less reliable. You can use the newest CoreTemp to see how it reports the power consumption and compare this with HM.

Am I correct that I'm not spending MUCH more money on electricity than I would like - because with C-states, EIST, Windows Power Saving profile, all enabled, the watts are low when the computer is being worked hard ?? It seems that is the case, even if the voltage is set at a constant 1.325v.

Yes, you are correct. With all power saving features enabled you are probably using only a few more watt hours.

I assume I am right because the reason the temperatures rise when stress testing, the CPU is working hard, drawing a lot more power and therefore getting hot.

Yes. But what I meant before was that higher temperature causes more power draw. The higher the temperature, the more power an electrical component consumes to provide the same efficiency. Of course, higher load means more power draw and more heat output. It's a vicious cycle.

If I am correct about not wasting too much energy, then I would like to know, "Am I wearing the CPU more than "reasonable" if I leave CPU voltage at a constant 1.325v, if it is mostly at idle while not playing games" ??

No, probably not. Even if you are wearing it a little more than normally, the CPU will still outlast its usefulness.

I don't have a clue about how "high" constant voltage affects the life of the CPU if it isn't being loaded with constant high workload much - maybe its better for it than having the volts changing all the time (wishful thinking).

I am no CPU engineer, but lowering the voltage means less stress on components, it can't be worse than constant higher voltage.