Updated: Tuning Cool'n'Quiet: Maximize Power And Performance

Editor's Note: This story first went live in November of 2009. After its publication, we went back and forth with AMD's power experts, discussing some of the conclusions drawn. With feedback from AMD, we've retested to clarify where optimizations are most likely to be made. We've also addressed a problem with Cool'n'Quiet observed in the previous piece, which turned out to be caused by an implementation of the technology, rather than the technology itself. Special thanks to AMD for its input.

Choosing the right processor is never an easy task. Like other choices in life, there are so many to choose from, and many factors to be considered.

Today, performance and heat are not the only factors we all have to consider. Power consumption is becoming increasingly important. However, most reviews and articles about processors still focus on performance for the most part. Often times, review benchmarking is performed without power management features turned on (an especially flagrant faux pas in the era of Intel's Turbo Boost, which requires those capabilities be enabled).

Is this a bad thing? It doesn't have to be in the context of testing specific theories. Performance is very likely the penultimate factor we all consider when buying a processor, or any other component for that matter. But as concerns about power consumption becomes increasingly important, we should try to always look at performance with power management features enabled.

Many view power management features as detriments to processor performance. Indeed, most reviews and articles that include performance evaluation with power management features turned on usually shows slightly lower numbers than when those features are turned off. However, many do not realize that, just like hardware and software, we can fine tune power management features either for more performance or lower power consumption. It’s not uncommon to tweak the BIOS, drivers, and operating systems for maximum performance, so why not the same with power management features?

Getting to Know Power Management

This article is an answer to that question. In order to fine tune power management, first we have to understand how it works. Power management throttles down the processor (or any other component for that matter), slowing it down to save energy when the workload is low. When a user alters the workload (by opening an application, for instance), power management throttles the processor back up to a higher clock rate until the workload changes again (basically, when the application or task is complete).

Although clock throttling is the most obvious effect of power management, it’s not the largest influence in lowering power consumption. Reducing voltage is what has the most significant impact. By throttling down the clock, processor manufactures can settle in on a much lower voltage for their processor. In addition to lowering power consumption, throttling clock and voltage will also reduce operating temperatures. Less voltage equals less power consumed and thus less dissipated as heat.

Today's processors offer fine-grained power management, able to run at a number of different clock rates and at many voltage levels. These different clock and voltage settings are called p-states (you know them as SpeedStep on Intel CPUs and Cool'n'Quiet on AMD chips). A modern processor can have at least two p-states--one for performance and another for power-saving mode. However, it’s not uncommon to see processors with more than two p-states. In addition to p-states, power management settings also include transition time and a workload level required to switch between p-states.

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  • DrgnRebrn
    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?
  • cyberkuberiah
    On the behalf of all readers , Welcome , and so to say , Hi! , Arnawa Widagda :)
  • Inf3rnal
    I'd like to see same article about Intel i5/i7 power setting tweaking.
  • razor512
    did any of these changes negatively effect performance?
  • 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.
  • nukemaster
    My old A64 3200+ is about to get this treatment
  • autoimmune
    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!
  • whiz
  • 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)
  • Jerky_san
    Anyone know where to get k10stat?
  • cushgod
    Google it Jerky
  • enzo matrix
    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.
  • mende21
    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.
  • fsjis1
    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.
  • arnawa_widagda
    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
    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.
  • Jerky_san
    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..

  • AMDnoob
    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.
  • nukemaster
    Is there a K8 equivalent app?
  • 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.
  • wira020
    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...
  • wira020
    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...
  • wira020
    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...
  • mende21
    After some more tweaking I was able to lower my 955 to 400mhz at 0.7v while idling. I can't reach 0.6v as in this article but at least I have it clocked lower. I also lowered the northbridge voltage a little in the slower p states. 3.8ghz still needs 1.45v core. Thanks again for the write up.
  • doron
    Why does the phenom 710's nb speed is at 1600mhz max? And why is the voltage at 1.25v? I have that cpu and the mobo (gigabyte 790fxt-ud5p) identified the stock voltage as 1.325.