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Tweaking And Undervolting

Updated: Tuning Cool'n'Quiet: Maximize Power And Performance
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Clearly, the default voltage settings are quite high and can use a good tweaking. But why stop there? Why not select the lowest voltage required for each p-state clock rate?

As a matter of fact, we did just that. However, we must remind you that each processor is different. You may be able to use the same settings as we did. But then again, you may not. You simply have to go through a process of trial and error to see what settings work for you while keeping things stable.

Note: originally, we didn't go into detail how these values were chosen. We decided on the following settings after testing the platform rigorously, running hours of several benchmarks, such as 3DMark Vantage, 3DMark 2001, SuperPi 4M, 8M, 32M, Prime95, WinRAR and a complete Cinebench R10 test run, without a hitch. At 800 MHz, running all Cinebench R10 tests took about 30 minutes, SuperPi 32M took roughly 1 hour 20 minutes, and the additional 3D rendering/video encoding took between four and eight hours.

Once those tests were completed, we retested the same values on a different motherboard. As a result, we unsurprisingly found that idle p-state values varied from board to board. For instance, originally we were able to run our Phenom II X4 955 processor at 800 MHz with just 0.6V core voltage on the Gigabyte 790GP-DS4H and -UD4. On the new platform, with a normal HT voltage of 1.2V, we could only get away with 0.75V.

Here are the custom voltage-optimized settings for each processor we tested.

Athlon X2 7750

Athlon X2 7850

Athlon II X2 250

Phenom II X3 710

Phenom II X4 945

Phenom II X4 955

We ran a barrage of stability tests for each of the above p-states (SuperPi, Prime95, Cinebench, 3DMark 2001), in addition to using each machine for several days. As far as we can tell, these settings are very stable with the samples on-hand. Of course, your experience may vary. Try using a small voltage bump (0.025V) to find the settings which work best for each p-state.

As you can see, we only change the core and northbridge voltage values. If you want more customized settings, you can also change the multiplier for each p-state.

Update: Experiences with Socket AM3 and Athlon X4 620

Below you can see the p-state values we were able to achieve on an AM3 platform with K10Stat. We've limited testing on this platform to just the Athlon II X2 250, Athlon II X4 620, and the Phenom II X4 955 Black Edition.

As noted earlier, we were unable to change the northbridge voltage values as we did with the AM2 board. There's still ample room for the core voltage alteration, though.

You would probably like to know the voltage values for each multiplier, right? Here's the voltage ramp data we gathered.

Athlon X2 7750

Clock
Core and Northbridge Voltage
2.2 GHz1.0V
2.5 GHz1.025V
2.6 GHz1.05V
2.7 GHz1.1V
2.9 GHz1.175V
3 GHz1.225V
3.1 GHz1.275V
3.2 GHz1.35V


Athlon X2 7850

Clock
Core and Northbridge Voltage
2.4 GHz1.0V
2.9 GHz1.125V
3.2 GHz1.275V
3.3 GHz1.35V


Athlon II X2 250

Clock
Core and Northbridge Voltage
1.7 GHz0.9V
2.4 GHz0.925V
2.6 GHz0.95V
3 GHz1.05V
3.125 GHz1.135V
3.25 GHz1.15V
3.375 GHz1.2V
3.5 GHz1.264V
3.625 GHz1.312V
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Top Comments
  • 13 Hide
    cyberkuberiah , November 16, 2009 7:00 AM
    On the behalf of all readers , Welcome , and so to say , Hi! , Arnawa Widagda :) 
  • 12 Hide
    Anonymous , November 16, 2009 11:12 AM
    Very good article! Undervolting it's a great tweak to make and most of the people don't even know that it is possible as well as overvolting, getting a power efficient processor for no money! Thanks tom's for caring about this matter.
  • 12 Hide
    DrgnRebrn , November 16, 2009 5:58 AM
    Nice article! I'm curious to know if the "e" CPUs can be affected in the same way, such as the Phenom II X3 705e. I have chosen this CPU for a HTPC build because of it's already low 65W TDP. Also, what are the effect to power usage when using ACC features & enabling dormant cores?
Other Comments
  • 12 Hide
    DrgnRebrn , November 16, 2009 5:58 AM
    Nice article! I'm curious to know if the "e" CPUs can be affected in the same way, such as the Phenom II X3 705e. I have chosen this CPU for a HTPC build because of it's already low 65W TDP. Also, what are the effect to power usage when using ACC features & enabling dormant cores?
  • 13 Hide
    cyberkuberiah , November 16, 2009 7:00 AM
    On the behalf of all readers , Welcome , and so to say , Hi! , Arnawa Widagda :) 
  • 3 Hide
    Inf3rnal , November 16, 2009 7:06 AM
    I'd like to see same article about Intel i5/i7 power setting tweaking.
  • 5 Hide
    razor512 , November 16, 2009 11:11 AM
    did any of these changes negatively effect performance?
  • 12 Hide
    Anonymous , November 16, 2009 11:12 AM
    Very good article! Undervolting it's a great tweak to make and most of the people don't even know that it is possible as well as overvolting, getting a power efficient processor for no money! Thanks tom's for caring about this matter.
  • 1 Hide
    nukemaster , November 16, 2009 11:18 AM
    My old A64 3200+ is about to get this treatment
  • -8 Hide
    autoimmune , November 16, 2009 11:36 AM
    Inf3rnalI'd like to see same article about Intel i5/i7 power setting tweaking.
    O my GOD i bet the writers at Toms Hardware had not thought of that, and are not currently in the process of writing that article!
  • -2 Hide
    whiz , November 16, 2009 12:12 PM
    Oops!
  • 0 Hide
    Anonymous , November 16, 2009 2:01 PM
    i love you guys. i have just the system that i am using as HTPC. i was wondering about ways to reduce the power usage as i dont use it for hardcore gaming or any other cpu intensive jobs. all i use it for watching blurays and tv and other movies and songs. i have an ASROCK 790gxh 128M mobo. and 1thlon x2 7750 kuma, that i bought from newegg for $59 (darn steal for the performance it gives. the machine has almost zero latency for any operation)
  • -2 Hide
    Jerky_san , November 16, 2009 2:19 PM
    Anyone know where to get k10stat?
  • 0 Hide
    cushgod , November 16, 2009 3:05 PM
    Google it Jerky
  • 0 Hide
    enzo matrix , November 16, 2009 3:25 PM
    Great article. I've been undervolting my Athlon 64 x2 in my laptop with K10stat for the past few months. The tx2500 models get hot. On load I went from a maximum of 90C to a maximum of 75-80C. Haha. no longer worried. Plus my fan doesn't go on maximum unless under full load anymore.
  • 1 Hide
    mende21 , November 16, 2009 3:31 PM
    It's great to see an in-depth article about k10stat. I discovered that program a couple of months ago and use it to underclock and overclock my 955. I hated disabling cool n quiet to overclock my processor and k10stat works great. I have it set to underclock to 400mhz at idle and overclock to 3.8ghz under load. After reading this, I think I can lower the voltages a little.
  • 2 Hide
    fsjis1 , November 16, 2009 3:34 PM
    It may be that AMD is making a purely dual core kuma and I am not aware of it, but I am fairly certain that the kuma series is actually a "phenom I" with two cores disabled, hence the L3 cache. I just did a google search and found people who have unlocked the extra cores on the athlon X2 7750 kuma. Nice article by the way I have been thinking about doing something like this to my PC's.
  • 9 Hide
    arnawa_widagda , November 16, 2009 4:50 PM
    First of all, thanks for all the comments and feedback.

    All Cool'n'Quiet 2.0 processors should work with K10Stat, so you should be able to use K10Stat with the Energy Efficient series.

    For those unfamiliar with K10Stat, here are some additional switches/options (insert these via the properties menu of your K10Stat shortcut).

    -lp:# - load profile# and write to MSR (activates a certain profile).
    -nw - Start K10stat with NoWindow (don't display window).
    -ClkCtrl:#(0-4) - Enable Clock Control (activates clock/core control).
    0:No Control
    1:UnGanged.
    2:Ganged (Load of Highest core).
    3:Ganged (Average load of all cores).
    4:Ganged (Load of Lowest core).
    -StayOnTray - puts K10Stat on the system tray. Use this option with “-nw” to keep K10Stat running. Very useful if you use sleep/hibernate.

    To those interested in Core i7/Core i5, a similar article is in the pipeline. We wanted to include the 32 nm refresh too, in addition to Core2Duo and Core2Quads, so we have to wait until (final) samples are out.

    About performance, performance differences and actual power consumption will be in the 2nd part - you'll see it soon. You might be (pleasantly) surprised.

    Thanks. Off to some more GPGPU testing.
  • -2 Hide
    Jerky_san , November 16, 2009 5:08 PM
    CushgodGoogle it Jerky


    People that say that tend to be fairly annoying.. Anyways I finally found a mediafire link.. all the geocities and rapid share links are dead..

    http://www.mediafire.com/?dywh3zhmk41
  • -5 Hide
    AMDnoob , November 16, 2009 10:33 PM
    can somebody tell me why my C'n'Q no longer functions? Go to my profile and look for the forum thread i started, it's all explained there.
  • 0 Hide
    nukemaster , November 17, 2009 12:45 AM
    Is there a K8 equivalent app?
  • -1 Hide
    Anonymous , November 17, 2009 12:54 AM
    I'm writing this on a 7750 (stepping 3) with a Foxconn A7GM-S motherboard, and CPU-Z reports 1.024V with Cool & Quiet on, and 1.312V at full speed. I'm not sure why you are observing different behavior.
  • -4 Hide
    wira020 , November 17, 2009 2:09 AM
    Nice article.. but it is a verrrrrrry lonnnnnnnnnnnng read.... hope you guys can simplify the article a bit... but nice research indeed... xD.. i'm just one of those lazy people that have a hard time reading thousands of words per page.. hehe...
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