Undervolting&Underclocking CPU

Speed addicts anonymous.

Moderator: Starfalcon

Undervolting&Underclocking CPU

Postposted on Mon Oct 01, 2012 2:36 am

Hey guys,

So these past days i have been playing around with my Phenom II 955 BE, namely i tried to find the best voltage settings for certain clock speeds. First i tried overclocking, i managed only 3,6 GHz at 1,40000V stable under OCCT 1h test and my temps got around 59 degrees Celsius (62 being TJmax according to AMD).

Since i didn''t notice much of an increase in performance i thought about undervolting and underclocking it to a point that it's "good enough" and doesn't bottleneck my GTX 560 Ti, too much atleast. So far i tried 3,2 GHz stable at 1,25000V, 2,8 GHz stable at 1,15000V but i don't think i'm satisfied yet, even though load temps did decrese to about 47-48 degrees during OCCT 1h test.

I'm thinking of a frequency that will be stable at 0,7-0,8V and that should be around 2 -2,2 GHz. I think that will be enough for web browsing and the games i play (except Tribes Ascend, will have to see how much of a fps drop i get).

But what about you guys, have you done this before? Are you undervolting/underclocking right now? Do you think i'm aiming too far with my sub 1V undervolt?
nVidia video drivers FAIL, click for more info
Disclaimer: All answers and suggestions are provided by an enthusiastic amateur and are therefore without warranty either explicit or implicit. Basically you use my suggestions at your own risk.
Arclight
Gerbil Elite
 
Posts: 705
Joined: Tue Feb 01, 2011 3:50 am

Re: Undervolting&Underclocking CPU

Postposted on Mon Oct 01, 2012 9:54 am

I couldn't lose more than about 20% of my voltage without the processor crashing, but that was a mobile Core 2 Duo so who knows how that translates.
Krogoth wrote:Care to enlightenment me?
grantmeaname
Gerbil Jedi
 
Posts: 1693
Joined: Fri Jan 18, 2008 7:49 pm
Location: Columbus, OH

Re: Undervolting&Underclocking CPU

Postposted on Mon Oct 01, 2012 11:33 am

I wanted to try the minimum voltage when i got home a few hours ago and surprise surprise, the minimum CPU voltage i can set in the BIOS is 1.10000V. So after my initial shock i remembered that CnQ lowers the voltage under that value for the the lowest power state....i've seen as low as 0.7680V i think. So i went back to the BIOS and i set the voltage to "Offset" and Auto and lowered the CPU frequency to 1600Mhz, thiking that CnQ will take care of the rest. Surprise again.......after starting the OCCT test, the automatic voltage was at 1.3800V herp derp.

At this point i started looking up an alternative and I've found a program called K10STAT which let's you set the voltage for each power state. I will try it out later though i must say i'm dissapointed about the BIOS settings........oh well.

I did test 1,1V at 2400MHz and it was stable under OCCT test, might try a higher setting later but at this settings CPU-Z reported it as being a 89W CPU which i found a bit funny
nVidia video drivers FAIL, click for more info
Disclaimer: All answers and suggestions are provided by an enthusiastic amateur and are therefore without warranty either explicit or implicit. Basically you use my suggestions at your own risk.
Arclight
Gerbil Elite
 
Posts: 705
Joined: Tue Feb 01, 2011 3:50 am

Re: Undervolting&Underclocking CPU

Postposted on Mon Oct 01, 2012 11:52 am

From an electrical point of view, undervolting will result in a larger decrease in performance than overvolting will result in an increase in performance. Transistors have a property called "threshold voltage," which is the minimum voltage at the transistor's gate required for the transistor to be considered "on."

The current of a transistor in a digital circuit is proportional to (Vgs - Vt) ^ 2. Where Vgs can be thought of (very loosely) as your supply voltage and Vt is the threshold voltage. I would expect the threshold voltage to be somewhere between 0.3 - 0.5 volts for that process. From the equation you can see that if Vt is 0.4 volts, then changing Vgs from 1.2 volts to 0.8 volts results in a decrease of current by 4x (note that this won't exactly translate to 4x less performance).

With that having been said, undervolting is not necessarily a bad idea. Power consumption in a CPU is proportional to the F(V^2) where f is frequency and V is voltage. Any amount that you can decrease V will lead to significant decreases to power consumption.

To answer your question directly, if 2.8 GHz works with a minimum of 1.15 volts, then you cannot hit a 2+ GHz frequency at 0.7 or 0.8 volts. You are aiming too far with your sub 1 volt goals. What I would do if I were you is find a performance target (frequency) that you deem acceptable, then undervolt until you are running at the minimum voltage for that frequency. Also, you should disable cores. If you don't want performance, then why are you running a 125W quad core chip?
"TORTURIS EXUVIAS EUNT"
Phenom X6 1090T @ 3.2 GHz
Sapphire Radeon 6950
TurtlePerson2
Graphmaster Gerbil
 
Posts: 1097
Joined: Sat May 26, 2007 9:08 am
Location: Plano, Texas

Re: Undervolting&Underclocking CPU

Postposted on Mon Oct 01, 2012 12:00 pm

The only time when I can justify underclocking is when you're trying to fit within certain thermal constraints. This often happens in HTPCs that recieve a recycled CPU (like a x4 955) that is grossly overpowered for the type of work it will be expected to do and has a high TDP (125W in this example) that doesn't work well with tiny enclosures having little airflow.

Keep an eye on your gaming framerates in CPU-limited games when you're underclocking like this. AMD's per-clock performance is definetly worse than Intel which is why AMD CPUs are always clocked higher to achieve the same "Intel-equivalent" performance. (ie, an AMD FX-4100 at 3.6-3.8GHz games roughly as well as an Intel G630 clocked at 2.7GHz as shown in the following article) If you're just looking for gaming performance, tests have shown that many modern games are more dependent on per-core performance than number of cores. If you're looking to save power and temps, try disabling one or two cores instead.
i5-3570K, ASRock Z77 Pro4-m, Asus GTX660 TOP, 120 GB Vertex 3 Max IOPS, 2 TB Samsung EcoGreen F4, 8GB G-Skill @1.25V, Silverstone PS07B
DPete27
Gerbil Jedi
Silver subscriber
 
 
Posts: 1714
Joined: Wed Jan 26, 2011 12:50 pm
Location: Madison, Wisconsin

Re: Undervolting&Underclocking CPU

Postposted on Mon Oct 01, 2012 12:21 pm

Thank you both for your input. As far as finding the best volatge for a particular frequency, i think i narrowed it down. Will try later to disable cores and see how far that takes me while using a game benchmark. I bought this CPU because at the time of purchase it had the best performance/price within my budget at that time(end of 2010 begining of 2011).

Right now though, i'm not seing much stress from the games i play in multiplayer so i'm just messing around i guess, it's not like i've set out to save electricity bills, i'd describe this more as an experiment born out of boredom. Next year or in 2014 i will upgrade probably but until then might as well have some fun. Who knows how locked platforms will be by then......
nVidia video drivers FAIL, click for more info
Disclaimer: All answers and suggestions are provided by an enthusiastic amateur and are therefore without warranty either explicit or implicit. Basically you use my suggestions at your own risk.
Arclight
Gerbil Elite
 
Posts: 705
Joined: Tue Feb 01, 2011 3:50 am


Return to Overclocking, Tweaking, & Cooling

Who is online

Users browsing this forum: No registered users and 2 guests