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Update: A “Broken” Cool'n'Quiet Implementation

Updated: Tuning Cool'n'Quiet: Maximize Power And Performance
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Update: We've received feedback from AMD regarding the power numbers and resulting analysis generated using this piece's platform. We are currently looking at other hardware combination in order to either validate or correct the initial conclusions drawn.

Update 2: After months of retesting, we finally chased down the problem to a BIOS bug with the TA790GX 128M that caused incorrect P-state settings to be applied. Updating the board's BIOS to the latest beta version fixed this problem. So, Cool'n'Quiet is not at fault for the results we saw previously. Instead, what we saw was a broken Cool'n'Quiet implementation. This does affect power consumption measurements with default settings for the Athlon X2 7750. But the other results are still valid, since they were taken with different motherboards that do not exhibit this behavior. The article have been edited to reflect this.

There are very subtle, yet very significant differences between these processors' implementations of Cool'n'Quiet technology. Let's check their respective default voltages, according to CPU-Z:


Default Clock
Default Voltage
CnQ Clock
CnQ Voltage
Athlon
2.7 GHz
1.312V
1.35 GHz1.36V
Athlon
2.8 GHz
1.280V
1.4 GHz1.04V
Athlon
3 GHz
1.408V
800 MHz1.056V
Phenom
2.6 GHz
1.28V
800 MHz1.184V
Phenom
3 GHz
1.424V
800 MHz1.072V
Phenom
3.2 GHz
1.424V
800 MHz1.04V


Using the TA790GX 128M, the Athlon X2 7750 default voltages set for higher p-states (idle mode) are actually higher than the default voltage for lower p-states (performance mode). Let's see how that strange anomaly affects power consumption at idle. On a motherboard with a proper Cool'n'Quiet implementation, the Athlon X2 7750 drops to 1.04V at idle, which is the same as the Athlon X2 7850.


Default System Power Consumption
CnQ-High Performance
CnQ-Balanced
Athlon X2 7750
81 watts
73 watts
79 watts


After the BIOS fix was applied, a quick test shows power consumption is about the same (74 watts average). In that regard, power consumption with and without Cool'n'Quiet is not that much different for the Athlon X2 7750 on a Biostar TA790GX 128M.

Athlon X2, Phenom X4, and Athlon II processors will use different clock rates for different cores, independent of each other. Though technically interesting, this adversely affects single-thread, single-core performance when Cool'n'Quiet is enabled, particularly in Windows Vista. Windows 7's scheduler manages threads more efficiently (bounding them around from core to core less often), based on our testing of Intel CPUs under the new operating system, so we'd expect older AMD CPUs to suffer less after an upgrade to 7.

Disclaimer note: of course, changing p-states settings is not without risks. An overly aggressive configuration will likely cause instability/crashes. There's also no guarantee that the savings will be worth your effort. In this regard, hacking p-state settings is no different than overclocking in that you are running the processor outside of its manufacturer's recommended specification. Continue at your own risk.

If you are unsatisfied with the default power management settings, there's a way to squeeze more power savings. As noted before, applications like K10Stat and PhenomMSRTweaker allow you to change this behavior so that clock changes are applied to all cores. You can also use them to edit register values used by Cool'n'Quiet, overriding the default values.

How about newer processors? Although the Phenom II X4 and X3 CPUs have changed the behavior of Cool'n'Quiet (proper setting of voltages and synchronous clock changes for all cores), you can still use those two applications to fine tune voltage settings.

There are other advantages associated with manipulating p-states settings. Unlike tweaking BIOS voltage settings, you can directly monitor the processor's voltage in real time. That means vdroop and offset are already taken into account. In addition, these settings are only applied when you want them to be applied. They are not saved in the BIOS. If a setting is too aggressive and causes problems (the familiar BSOD), a reset will revert their values to default.

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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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