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Voltage Ramp And Power Consumption

Updated: Tuning Cool'n'Quiet: Maximize Power And Performance
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An interesting bit of info we were able to glean from testing these processors was the already-known relationship between voltages and power consumption, both at idle and under load. In the graphs below, the voltage values are normalized to the first point (for example, 1.0V = 100%). All of the nominal voltages for each setting are available on the table.

Disclaimer: AMD replied to our original story stating that the p-state setting are chosen carefully to achieve an optimal blend of performance and power consumption, making sure there's enough power savings between each p-states. However, as with most overclocking experiments, sometimes these setting may not be “as close to the edge” as possible. So, adding to our earlier disclaimer, changing p-state settings, voltages and clocks may cause instability and crashes, negating the power savings under default settings. As always, your mileage will vary.

Athlon X2 7750

Clock
Core and Northbridge Voltage
Idle
Load
2.2 GHz
1.000V
60 watts88 watts
2.5 GHz
1.025V
61 watts90 watts
2.6 GHz
1.050V
62 watts92 watts
2.7 GHz
1.100V
65 watts97 watts
2.8 GHz
1.125V
66 watts100 watts
2.9 GHz
1.175V
69 watts108 watts
3 GHz
1.225V
75 watts113 watts
3.1 GHz
1.275V
76 watts120 watts
3.2 GHz
1.350V
84 watts135 watts


Some interesting data can be seen here. First, you can pretty much get away with running this processor at 2.5 GHz with minimal impact on power consumption, both at idle and load. The highest optimal setting we can get away is 3.1 GHz with a synchronous core and northbridge voltage of 1.275V. Beyond that, you'll need more voltage for each clock rate/multiplier jump.

Notice that you can reach 3.1 GHz with the default voltage (1.275V). That's actually not entirely correct. The core voltage is 1.275V, rather than the default voltage of 1.325V. The effect is that power consumption (120 watts) is not far off from the default settings (110 watts, 2.7 GHz @ 1.325/1.275V). This means you get more performance, while “only” consuming 10 watts more. Even more interesting, idle power consumption is about the same as the default settings (75 watts).

If you really want to tweak your p-state settings, the best combination would be 2.5 GHz for the idle p-state and 3.1 GHz for the performance p-state.

Athlon X2 7850

Clock
Core and Northbridge Voltage
Idle
Load
2.4 GHz
1.000V
78 watts99 watts
2.9 GHz
1.125V
83 watts116 watts
3.2 GHz
1.275V
97 watts149 watts
3.3 GHz
1.350V
100 watts
174 watts


The lowest voltage we were able to use with this processor is 1.0V, so you can practically run the processor at up to 2.4 GHz for “free.” We didn’t test as many settings as we did with the Athlon X2 7750, mostly due to time constraints. However, you can see that after 2.4 GHz, the voltage ramp is divided into three stages. The optimal point between clock rate, voltage, and power consumption for this processor seems to be 2.9 GHz. After that, power consumption scales up much faster than voltage. At 3.2 GHz, we’re already hitting 149 watts under load (without an add-on graphics card, mind you) and at 3.3 GHz, the power consumption is just too high to justify the performance (174 watts).

If you were to choose between the Athlon X2 7750 and 7850, it would seem the Athlon X2 7750 has the better value. It’s slightly cheaper and actually consumes less power. You still get the same capacity L3 cache, the unlocked multiplier feature of Black Edition processors, and roughly the same upper limits of overclocking.

Athlon II X2 250

Clock
Core and Northbridge Voltage
Idle
Load
1.7 GHz
0.900V
62 watts76 watts
2.4 GHz
0.925V
64 watts80 watts
2.6 GHz
0.950V
65 watts83 watts
3 GHz
1.050V
66 watts90 watts
3.125 GHz
1.135V
66 watts91 watts
3.25 GHz
1.15V
66 watts93 watts
3.375 GHz
1.2V
66 watts99 watts
3.5 GHz
1.275V
67 watts
105 watts
3.625 GHz
1.325V
69 watts
110 watts


One thing that really jumps out with this processor is how low its idle consumption is, regardless of clock speed. So, if you spent more time idling, you could run this processor without power management and see some significant power savings. Yes, we did check to see if the processor throttled down its clock, and it didn’t. Another interesting point is that we can actually get away with a slightly lower voltage (0.025V) than before. This explains the additional 10 watt drop at the processor’s default 3 GHz clock rate when under load.

The Athlon II X2 250 may lack the L3 cache of its predecessors, but with about the same voltage, it can run about 400 MHz faster. In fact, it can run at 3.625 GHz and still offer the same level of power consumption as our Athlon X2 7750 sample (2.7 GHz @ 1.1V). Although it doesn’t offer unlocked multipliers, it does serve up higher overclocking headroom. And of course, it works with both DDR2 and DDR3 memory.

One important feature that the Athlon II X2 250 has (and both the Athlon X2 7750 and 7850 lacks) is p-states, or rather the use of more than two p-states. Looking at the idle and load numbers, you probably only need two p-states, the lowest at 1.7 GHz and the intermediary/highest p-state at 3 GHz. If you’re overclocking, you can set the two additional p-states to 3.375 GHz and 3.625 GHz.

If we compare these power consumption numbers with default settings, we can see that we were able to run the processor at 3.625 GHz and still remain in the same power envelope (73 watts idle, 110 watts load).

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  • 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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