Undervolting and Power Consumption

[ctsoth]

Hello,

Processor a8-3870k.
F1-A75 Pro/CSM
Windows 7 Ultimate
2x crucial m4

After running an overclocked system for several months my OS started to develop some issues, that is windows update didn't work anymore, it would just lock and stop responding. I decided to reformat, and update BIOS as a new update was just released a few days ago. [New BIOS update claims to improve system stability...] Also, I really don't want to risk any data corruption......

I used to do a lot of gaming, DOTA 2, Diablo 3, World of Tanks, Eve Online, Minecraft... I don't really have time to game anymore, and use the computer for productivity, that is word processing, internet browsing, HD video streaming, HTPC use etc. and decided to re-purpose my setup to be as energy efficient as possible.

I'm currently experimenting with voltage offset to decrease peak power usage. Stock maximum voltage for the a8-3870k according to AMD is 1.4125 @ 3ghz. *1

I'm still experimenting to discover my minimum voltage, and I'm on my second decrease, right now I have Prime95 running, 4 instances of large FFTs, Asus Probe II, CPU-Z, Pandora, and Firefox all running @ 1.368v. Prime has been running for about .6 hour now, going to let it go another half hour or so before I decrease voltage further.

1.4125 - 1.368 = .0445 decrease in peak voltage @ 34C full load, ambient temperature 70F. I will see if I get my hands on something to get a reading on total system power usage...

Edit: Currently Stress Testing @ 1.248v, stock voltage 1.4125v, voltage decrease of .1645. Full Load 31C, 87.8F. Ambient Temperature 21.1C, 70F

I plan also to install Ubuntu soon on my second hard drive, and run it virtually but I really don't know how to do that sort of thing... Any links or suggestions would be nice.

Thanks,
Chris

*1 http://products.amd.com/pages/DesktopAPUDetail.aspx?id=30&f1=&f2=&f3=&f4=&f5=&f6=&

 

[Idontcare]

I like this idea as well.

AMD (and Intel) have to set their spec Vcc's based on the necessity of the CPU being stable at stock clocks while operating under the most demanding corner cases allowed per the spec (application loading, temperature, voltage fluctuations, etc).

If you, as the end-user, can intentionally avoid taking your rig to one of those corner cases then you don't need the voltage that AMD (or Intel) felt compelled to have the mobo provide the CPU.

For example, don't run IBT as an application 24/7/365 and you don't need to worry about supplying enough voltage to run IBT 24/7/365.

Likewise if you buy a 3rd-party HSF and keep the max operating temperatures well below the TJmax or spec'ed max temp then you don't need to feed your CPU as much voltage as AMD (or Intel) was compelled to spec...etc etc.

In other words, the operating voltage set by the manufacturer is set so that all the extreme operating cases are covered and the CPU remains stable.

Avoid taking your CPU into those extremes and you can scale back the voltage, no different than what the manufacturer would have done had they not needed to account for the possibility of those extreme condition in the first place.

My Ivy Bridge i7-3770k is an example of this. At stock clocks and under full load, Intel has the Vcc set to 1.243 Volts per the VID.

But I can scale that back to a mere 0.998V with the stock cooler, stock TIM, stock everything simply because I keep my computer inside an air-conditioned room that results in the max operating temps peaking at 80°C under IBT loading versus Intel needing to make sure that the CPU is stable even when it heats up to 105°C (TJmax) per chance I live in the Sahara desert with no AC.

It is no miracle that I can undervolt (or that any of us can), at the same time it is no wonder why AMD (and Intel) must set the stock Vcc so high for these CPU's. They must cover corner cases for potential operating conditions that we can intentionally/knowingly avoid as enthusiasts.

I'm curious though, with your specific processor, how much power are you able to save in undervolting the iGPU?

On my rig I use a GTX460 and it alone consumes some 80W. Undervolting my 3770k does me almost no good because the GPU is such a power hog. I can't use the iGPU on my 3770k because of the way Intel segmented the chipset market, my $350 MIVEZ mobo doesn't have a video-output for the iGPU :| (note to Intel - sometimes you suck in ways that are beyond annoying)

 

[ctsoth]

Thanks for the thoughtful reply IDC. I have not touched the voltage for the iGPU yet... Once I find my stable minimums I will do a power comparison running Prime & OCCT at reduced voltage and stock. Lano has great idle power consumption as the processor clocks down to 800mhz. *1

It should be noted, I use the following aftermarket cooler, probably overkill for my setup, but I would like to maximize product life, as I burnt out my Core2Duo e6300 @3400mhz over a course of years. *2

Strangely I find this undervolting adventure to be more fun than overclocking.

*1 http://www.anandtech.com/show/4476/amd-a83850-review/9
*2 http://www.noctua.at/main.php?show=productview&products_id=37&lng=en

Edit: I went with the C14 as the top down airflow blows air over my chipset and ram, it does clear the following memory modules: http://www.newegg.com/Product/Product.aspx?Item=N82E16820231455

 

[Magic Carpet]

On my rig I use a GTX460 and it alone consumes some 80W.

Fermi undervolts fairly well and your card isn't an exception. Have you tried yet?

 

[ShadowVVL]

I was thinking of doing this with my q9550 since with Im not ocing but haven't got around to it.

I might try it tonight and drop the voltage from 1.160 to 1.140 run 8h stress test then try 1.120.

 

[dma0991]

I plan also to install Ubuntu soon on my second hard drive, and run it virtually but I really don't know how to do that sort of thing... Any links or suggestions would be nice.

You could install Virtualbox and use Windows as the host OS and Ubuntu as the guest OS and specify where the .vdi should be placed by default, in a secondary drive for your case. However, you could run a dual boot pretty easy with both Windows and Ubuntu on the same drive with GRUB handling which OS to boot.

There is another method of installing Ubuntu in a separate drive and specifying which OS to boot first by changing the boot priority of the drives in BIOS. If Windows is in HDD A and Ubuntu in HDD B, placing HDD B first in the boot priority would only start Ubuntu and vice versa.

 

[ctsoth]

You could install Virtualbox and use Windows as the host OS and Ubuntu as the guest OS and specify where the .vdi should be placed by default, in a secondary drive for your case. However, you could run a dual boot pretty easy with both Windows and Ubuntu on the same drive with GRUB handling which OS to boot.

There is another method of installing Ubuntu in a separate drive and specifying which OS to boot first by changing the boot priority of the drives in BIOS. If Windows is in HDD A and Ubuntu in HDD B, placing HDD B first in the boot priority would only start Ubuntu and vice versa.

Thank you for the info, I want to run it as a virtual machine so I can have both operating systems active at the same time....

It looks like the minimal voltage is 1.248v. I may be able to get it down one more tick on the offset, but I'm going to let prime run for a few hours to ensure the system is perfectly stable. I'll start on the iGPU voltage tomorrow and see about getting some system power consumption information, stock vs reduced voltage.

Any advice on undervolting the northbridge? What should I look out for, or is it kind of a waste of time? Are there any symptoms of inadequate cpu voltage beyond the BSOD?

Edit: Currently Stress Testing @ 1.248v, stock voltage 1.4125v, voltage decrease of .1645. Full Load 31C, 87.8F. Ambient Temperature 21.1C, 70F

 

[dma0991]

Thank you for the info, I want to run it as a virtual machine so I can have both operating systems active at the same time....

Just follow the step by step guide on Virtualbox while creating a new virtual disk, its pretty straight forward. After installation of Ubuntu to the virtual disk, install guest additions and set up a shared folder between the host OS and guest OS. It will be a lot easier if you want files on your host OS to appear in the guest OS. Allocate half the number of cores in your machine to the guest OS, for Ubuntu it works best with 2 or more. There are plenty of tutorials and guides for what I've mentioned.

 

[ctsoth]

Unless I'm missing something it appears as though I am unable to undervolt the iGPU.

Total System Power Consumption Results, measured from the outlet. Supposedly 0.2% margin of error:

a8-3870k
Asus f1-a75 pro/csm
16g gskill 1866
2x crucial m4
7x 120mm low rpm case fans
1x lg bluray optical drive
noctua c14
antec earthwatts 400 psu

@ 1.260v
Idle: 50w
Full Load, Prime Large FFTs: 125w
Full Load, Prime Large FFTs, OCCT GPU 3d: 145w

 

[ctsoth]

Forgive the Double Post

Power Consumption Results @ Stock Voltages [Keep in mind this is the entire system as measured from the outlet, I don't know how to directly measure CPU wattage]:

Idle: 50w
Full Load, Prime Large FFT: 152w
Full Load, Prime Large FFT, OCCT GPU 3d: 167w

Summary: Idle consumption is unchanged, as expected, because minimum voltage core is not scaled back with voltage offset. Load consumption is 27w lower while undervolted, CPU + GPU load is 22w lower while undervolted.

That is fairly substantial energy savings, assuming my 3870k draws about the same amount of power as the 3850 in anands review, cpu draw @ load should ~= 101w while in the undervolted state, putting it dangerously close to sandy bridge dual core...

 

[Idontcare]

Unless I'm missing something it appears as though I am unable to undervolt the iGPU.

:hmm: interesting. I'm sure it is completely unrelated but I checked my 3770k and I can't undervolt the iGPU either. The BIOS only allows for over-volting, no undervolting.

I wonder why that is the case?

 

[ctsoth]

:hmm: interesting. I'm sure it is completely unrelated but I checked my 3770k and I can't undervolt the iGPU either. The BIOS only allows for over-volting, no undervolting.

I wonder why that is the case?

My first thought is that there isn't much room to scale the voltage down, but that doesn't really make any sense knowing what we know about factory voltage settings. My second thought is that motherboard manufacturers didn't bother with it, assuming nobody would ever do it.

 

[Soulkeeper]

I did this a lot when I first got my llano
A major point to consider is the powernow steps, you could be 100% stable at full clock with your selected voltage, and even stable at the lowest clock with the -.4v offset. But one of the inbetween steps can be unstable.

So really each time you change the voltage you are subjecting 8 different clock/voltage pairs to potential instability(even if only rarely used).
mild desktop usage could expose them where stress testing won't.

 

[Yuriman]

Do AMD chips have anything equivalent to a turbo-only voltage adjustment?

 

[Dufus]

My first thought is that there isn't much room to scale the voltage down, but that doesn't really make any sense knowing what we know about factory voltage settings. My second thought is that motherboard manufacturers didn't bother with it, assuming nobody would ever do it.

It's can be done on Asrock Z77 Pro3 (±100mV) and iGPU adjustment granularity is pretty big, 50mV, but then it is a low cost board. Never used it though.

 

[Idontcare]

My first thought is that there isn't much room to scale the voltage down, but that doesn't really make any sense knowing what we know about factory voltage settings. My second thought is that motherboard manufacturers didn't bother with it, assuming nobody would ever do it.

I like how you think, makes sense to me. The mobo makers probably just figured no one would be interested in undervolting their iGPU since most people using an iGPU are probably more likely to be intersted in OC'ing the iGPU and so they will want to be able to overvolt it (not undervolt it).

 

[Vinwiesel]

Do AMD chips have anything equivalent to a turbo-only voltage adjustment?

I'm curious about this too. I have an athlonX2 5200 system with an 8800gts that I'm trying to reduce the power on as it's no longer a gaming rig. I have cool and quiet enabled, but it didn't make much difference in the overall system power. The system seems to bounce between active and idle every half-second.

The 8800 is rated at about 55watts idle, due to having no idle clock/voltage mode. I cut 10w by underclocking with Afterburner, but would have to hard-mod any voltage reduction. Tempted to just swap in a $30 GT 520, but the math tells me it would take 3 years for the power savings to pay for it.

 

[ctsoth]

I'm curious about this too. I have an athlonX2 5200 system with an 8800gts that I'm trying to reduce the power on as it's no longer a gaming rig. I have cool and quiet enabled, but it didn't make much difference in the overall system power. The system seems to bounce between active and idle every half-second.

The 8800 is rated at about 55watts idle, due to having no idle clock/voltage mode. I cut 10w by underclocking with Afterburner, but would have to hard-mod any voltage reduction. Tempted to just swap in a $30 GT 520, but the math tells me it would take 3 years for the power savings to pay for it.

I don't know enough about various AMD architectures to answer that question. I don't know if the processors that support turbo mode, or turbo boost or whatever have a separate turbo voltage, or if they just ramp to a higher maximum voltage. The way my particular processor works, is it only ramps up voltage as frequency/load is increased.

The undervolting that I have done does nothing for power consumption at an idle state, and saves 20-25 watts at full load depending on the situation. It is important to note, that my computer spends a lot of its time at an idle state, or at a moderate level, with only brief periods at full load. Therefore my real world power savings are marginal, but learning about voltage states and the direct and measurable impact on power draw has been a fascinating experience. I find that I am interesting in overclocking the system now just see how big of an impact it has on total power consumption.

That card at an idle power consumption of 55w is drawing a lot of power, but I agree with your assessment that replacing it would probably be fiscally non-productive.

 

[Soulkeeper]

I just saw this cool feat

apparently that's an i5 system that he managed to get to idle at 5.9W
he's claiming it's the lowest in the world

 

[SPBHM]

I was able to lower the power consumption of my old athlon X2 by 40w with some undervolting (with the default clock),
it's certainly useful

 

[ctsoth]

Check this out. Download links do not work on main page, but the top nav bar will bring you to links that work. Utility for undervolting/underclocking lano, primarily meant for laptops.

http://code.google.com/p/fusiontweaker/