CPU undervolting questions

Hello everyone,

I have seen some members on NBR undervolted their CPUs, anywhere from -50mV to -100mV.

How do you undervolt exactly? I downloaded Intel XTU, and I am not sure which voltage settings to work with. Do i undervolt Core, Cache, Graphics, or all of them?

Does undervolting actually do anything? I have heard that some people had their CPU temps dropped by a few Celsius, is that true? Does it also drop power consumption, or the CPU will just increase Amps to compensate with the lowered voltage?

Lastly, does undervolting void warranty? Thanks.

 

You want to undervolt the core voltage offset and cache voltage offset.

Undervolting works because each CPU is unique, and requires a slightly different amount of power to run properly. However, Intel simply takes the worst-case scenario approach, and assigns every CPU the same voltage. By undervolting, you're simply giving your CPU the exact amount of power it needs to run properly, and by reducing the voltage you reduce heat generation. So long as you undervolt properly (testing thoroughly to make sure the CPU can run properly at any given voltage) then you won't harm your CPU in any way, won't void your warranty, and should see a temperature drop of at least a few degrees, all while retaining the full performance of your CPU.

 

You can undervolt your Dynamic CPU Voltage Offset, Processor Cache Voltage offset, and the Processor Graphics Voltage Offset (if you are using intel integrated graphics, no effect if using dedicated graphics)

The point of undervolting is to reduce power consumption and heat generation without losing performance.For example on my Alienware 18, I have a 4930MX with default multipliers of 39,38,37,37. I bumped those all up to 40,40,40,40 and started fiddling with the voltage offset and the cache voltage offset by increments of -mV. Be sure you have saved/closed out of anything important because if you hit an unstable value, your computer will crash, so you don't want to lose anything important. After fine tuning my system, not only did I increase my multipliers, but I also managed to get a -100mV dynamic CPU voltage offset and a -25mV CPU cache voltage offset. I am very happy with those results!

 

Thanks for the answers. How should I undervolt, like, -5mV at a time?

How can I tell if it's stable? Should I run some benchmarks to make sure if it's stable? Any good benchmark recommendations? I am not sure if I should use Prime 95 for this...

 

Your computer would be stable when you are able to change the settings, and it doesn't crash the computer when running in normal usage, as well as running benchmarks. You want it to be able to run a benchmark for a little while without causing any issues on the computer. If your computer crashes, then just keep adjusting the settings until you get to the point where it won't.

Sure, Prime 95 should be a good one to run I would think.

 

Right now, I am just using the stress test that came with the Intel XTU, and test it for 5 minutes. It seems to stress the CPU to 100% load, would it be fine as well, or should I use other tools to benchmark? How long should i stress test it before I undervolt further?

 

Is it okay to undevolt the iGPU as well? Just trying to squeeze a bit more battery here, if not... lower temps would be good too.

 

Start with the OP in the P75xZM owner's lounge.
http://forum.notebookreview.com/thr...owner´s-lounge-welcome-to-the-batcave.767105/
This post
http://forum.notebookreview.com/thr...-to-the-batcave.767105/page-771#post-10066106
This post
http://forum.notebookreview.com/thr...-to-the-batcave.767105/page-778#post-10069636
That should get you started.

I don't use Prime 95. There's mixed opinions about it with Haswell. I use XTU to set the voltage. I started with Core Voltage Offset. Others started with Cache. I, pretty much followed, @jaybee83 and @ajc9988 in the P77xZM thread, as a guide. After the cold boot I run POV-Ray on all cores, under the Render Tab - Run Benchmark (All CPUs). It's a short stress test. Then I run OCCT. In the options I change the cut off temp to 95C°. Throttling starts at 96C° for the 4790K. I run it for 20 minutes. Then I run x264 V2. I run three loops, about 30 minutes, on 16 threads and normal priority. After those I use the computer normally and finally idle time for the rest of the day / night. You need to test it for stability; stressed, under normal usage and idle. Passing the stress tests and crashing surfing the web or gaming happens. We don't want that.

I started at -50mV VCore, passed that. The next day I went to -75mV, crashed in OCCT and eventually was stable at -60mV. The next day I started VCache at -50mV and continued the process.

I use XTU to monitor voltage and TDP. For temps HWInfo64. I log the results. I record ambient temps too. All stress testing with max fans.

The stress test in XTU is OK but not as stressful as OCCT. So far, every crash, for me, has been in OCCT. Temps were not high. It just wasn't stable. That's OK, you do want it to crash. Find a stable point and then decrease the undervolt -5mV for everyday usage. When I get my max undervolt for the chosen frequency, 40x all cores, for example, I will add other stress tests / benchmarks for extra confidence that it's stable. That's when I use the stress tests in XTU.

 

So far I got -75mV on core Voltage... I am not sure if I should go even further...

 

On the two different CPU's I've undervolted I've gotten stable settings at -125mV and -50mV. Its changes per CPU.

 

I ordered a Sager with an i7-6820HK overclockable CPU. I'm new to overclocking and undervolting. Can I get the best of both worlds by setting up one profile that runs undervolted at standard clocks when on battery and another profile that increases the clock speeds and voltages to match when plugged in? Can this be automated so that I don't have to manually switch from undervolted/standard to less-undervolted/overclocked? Do I need to have an overclockable CPU or could I also undervolt a CPU with locked multipliers like the i7-6700HQ? Thanks!

 

If you do it on Intel XTU, you will have to make a profile to switch. I can undervolt on my i7-4720HQ, so you don't need a overclockable CPU to undervolt.

 

So far I think I hit the limit of -75mV for the Core voltage offset. When I set to -85mV, after I click end for the OCCT benchmark, my computer crashed. Does it mean I hit the limit?

 

The undervolting guide in another forum on this site recommends using RMClock for undervolting. Another guide on OC3D recommends CPU-z. It looks like Throttlestop can do it, too. Can anyone advise on the relative pros and cons of each of these programs?

 

Probably. Set it to -80mV and see. I had it crash while running OCCT and taking a screenshot. That said unstable to me.

 

I am in the process of undervolting the cache voltage, I will try -80mV core later today. Looks like OCCT really works.

Sent from my potato running on Android 5.0.1

 

It's definitely a tough program but that's a good thing when stability is the goal. Temp was never an issue in any crashes I've had. I've had it crash in a minute and over 15 minutes. So, I always run it 20 minutes before moving on. I will run it longer for longer term usage at an UV.

 

I have been only running it for 5 minutes... looks like I should run it longer...

Should core and cache voltage be the same? Or they can be different?

 

They can be different.

 

Great thread! I've been interested in this topic.

Quick question: do you need to have Intel XTU running for the undervolting to take effect? Is it something that you set once and then don't need to run the program again until you want to make another change?

 

Once you make your settings, apply them, and you don't need Intel XTU running to get undervolting to take effect.

 

Cool! Thanks for the response.