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

Measured Power Consumption And Methodology

Of course, tweaking voltage is just a means to an end: measuring the performance per watt of these processors. We'll start the traditional measurements of system power consumption at idle and with load.

Testing for idle consumption is done on the Windows desktop, from when the system is turned on until 15 minutes after boot. We think 15 minutes is enough time for all Windows background process to settle down, providing the least amount of burden on the processor. For this test, we did not disable SuperFetch, indexing, or the Windows Aero interface.

Testing under load was accomplished by running WinRAR's built in benchmark, which puts heavy load on all cores. The key here is heavy load, but not full load. For those who are interested in peak load numbers, we also measured the power consumption of all processors when running Cinebench R10 multi-threaded benchmark, which does fully utilize all cores.

A Side Note

Please note that the Athlon X2 7850, Athlon II X2 250, Phenom II X4 945, and 955 are running on the Gigabyte GA-MA790GP-DS4H, while the Athlon X2 7750 and Phenom II X3 710 are running on the Biostar TA790GX 128M. There is a good reason why we chose to use two motherboards for these tests; the two boards represent different market segments.

A quick check on Pricegrabber revealed the Biostar TA790GX is selling for around $100, while the Gigabyte GA-MA790GP-DS4H is about $150. The $50 you save going with the Biostar board can go into the processor instead, which means you only have to pay around $25 more to get the Athlon X2 7750 or $for the Phenom II X3 710. However, the Gigabyte GA-MA790GP-DS4H offers more tweaking options, so if you really want to squeeze as much performance as possible, it’s a very good board and a suitable match for the Phenom II X4 945.

There are a few interesting tidbits we observed with Biostar's TA790GX 128M. The motherboard will only run our Phenom II X4 945 and 955 samples at 800 MHz, no matter which BIOS version or settings we used. The company's official response was that the board does not support these processors. The company won’t go into details about it other than “it’s a hardware limitation,” and recommends that enthusiasts who want to use the Phenom II X4 945 or 955 choose the newer TA790GX A3+ with DDR3 memory instead. It also assured us that that board will work with a Phenom II X4 965 BE.

We did find a workaround for this problem. By using AMD’s Overdrive utility we were able to change the multiplier so these two processors operate at their default clock rates. Obviously, you’ll need to adjust the voltage too. One caveat with this trick is that the northbridge and memory controller will only run at 1.6 GHz, rather than 2 GHz.

The TA790GX 128M would also “forget” the p-state changes we applied when the system would wake from sleep/hibernation, resetting the values to default Cool'n'Quiet settings. With the HyperTransport interface overclocked, the system would crash, requiring a reset. We did not see this behavior with either of the Gigabyte boards.

These measurements were taken with different power profiles: No Management (we turned off Cool'n'Quiet from the BIOS), Balanced (Cool'n'Quiet is enabled on the BIOS, Windows power policy set to Balanced), and Optimized (Cool'n'Quiet enabled in the BIOS, Windows power policy set to Balanced, the processor running with lower core and northbridge voltages, shorter p-state transition time and synchronous clock changes or “Ganged” in K10Stat).

  • 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?