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By default, you can’t change the power management features of a processor. There are no settings to tweak in the BIOS (unless you count the ability to turn power management on and off).
However, you can run applications like RMClock, CrystalCPUID, K10Stat, and PhenomMSRTweaker to customize your power management configuration. These applications allow you to override default settings used by Intel’s SpeedStep and AMD’s Cool'n'Quiet. The only requisite is making sure each of the power management options you tweak is actually enabled in your motherboard's BIOS.
What, exactly, can you accomplish with these applications? In addition to choosing the settings for each p-state, such as operating clock rates and voltages, you can also change transition time between p-states and the level of workload required for a p-state change. It’s easier to explain fine tuning p-states like this:
Changing upward p-state transition to a lower value means you switch from power-saving mode to performance mode faster, so there’s little delay when running applications. Changing downwards p-state transition to lower values means you switch from performance mode to power-saving mode faster, conserving power when you don’t need the performance any more.
- Phenom II X3 710...
Changing the upward workload level means the processor won’t switch to a higher p-state as long as the workload is below that threshold. Vice versa, changing the downwards workload level means the processor will only switch to a lower p-state if the workload drops to that level or goes lower.
How does transition time relate to workload? The lower the value you use for transition time, the faster you switch to another p-state once the processor hits the workload level you specify. Of course, if you use a higher value, p-state transitions occur at a slower rate.
For processors with more than one core, you can even specify how to calculate the workload. The options can range from average workload to the highest workload on one core to a minimum workload on one core.
The trick to striking the best balance between performance and power consumption is finding the right combination of p-states, transition times, and workload levels. The right combination will not only allow you to realize performance very close to what you might expect without power management enabled at all, but also effectively conserve power and reduce operating temperatures.
The Tools of the Trade
To measure the effects of power management on performance (and our fine tuning efforts), we need a handful of tools.
In addition to the usual benchmarks and software utilities mentioned above, we need a tool to log throttling. Why? To see whether or not unnecessary throttling is happening. Luckily, RMClock provides this feature. Unfortunately, it lacks the ability to independently manage the power management features of newer AMD processors. We also need a power meter in order to actually measure the power we save. A Watts Up? PRO power meter is used for this purpose.
In this article, we are going to use six AMD processors: the Athlon X2 7750 Black Edition, Athlon X2 7850 Black Edition, Athlon II X2 250, Phenom II X3 710, Phenom II X4 945, and the Phenom II X4 955 Black Edition. Because RMClock is unable to manage power management features of these processors, we have to use either K10Stat or PhenomMSRTweaker. We opted to use K10Stat because it has the ability to manage more than just one p-state.
There are some architectural and design differences between these processors, but we won't discuss them in detail here. The Athlon X2 7750 and 7850 are still built on AMD's 65nm process, while the others are manufactured on the new 45nm process. The Athlon X2 7750, 7850, and Athlon II X2 250 are true dual-core processors, with no disabled cores or cache. The Phenom II X3 710 is basically a “failed” Phenom II X4. AMD has disabled the fourth core (with its corresponding L2 cache), although the 6MB L3 cache remains intact.
Here's some additional info on these processors:
| Core Clock | Northbridge Clock | L2 Cache | L3 Cache | |
|---|---|---|---|---|
| Athlon X2 7750 | 2.7 GHz | 1.8 GHz | 2 x 512KB | 2MB |
| Athlon X2 7850 | 2.8 GHz | 1.8 GHz | 2 x 512KB | 2MB |
| Athlon II X2 250 | 3 GHz | 2 GHz | 2 x 1MB | N/A |
| Phenom II X3 710 | 2.6 GHz | 1.6 GHz | 3 x 512KB | 6MB |
| Phenom II X4 945 | 3 GHz | 2 GHz | 4 x 512KB | 6MB |
| Phenom II X4 955 | 3.2 GHz | 2 GHz | 4 x 512KB | 6MB |
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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?
On the behalf of all readers , Welcome , and so to say , Hi! , Arnawa Widagda
I'd like to see same article about Intel i5/i7 power setting tweaking.
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.
My old A64 3200+ is about to get this treatment
I'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!
Oops!
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)
Anyone know where to get k10stat?
Google it Jerky
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.
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.
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.
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.
Google 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
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.
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.
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...