Finally, Cool 'n' Quiet You Can Use

Modern day microprocessors have many operating frequencies they can choose from; these are called p-states. The original Phenom only had two p-states: full frequency and 1/2 frequency. A Phenom 9950 2.6GHz would either run at 2.6GHz or 1.3GHz. The original Phenom was the first quad-core x86 CPU to allow each core to operate at an independent p-state. All of Intel's quad-cores at that point required all four cores to run at the same p-state.

In theory, the AMD design made sense. If you were running a single threaded application, the core that your thread was active on would run at full speed, while the remaining three cores would run at a much lower speed. AMD included this functionality under the Cool 'n' Quiet umbrella. In practice however, Phenom's Cool 'n' Quiet was quite flawed. Vista has a nasty habit of bouncing threads around from one core to the next, which could result in the following phenomenon (no pun intended): when running a single-threaded application, the thread would run on a single core which would tell Vista that it needed to run at full speed. Vista would then move the thread to the next core, which was running at half-speed; now the thread is running on a core that's half the speed as the original core it started out on.

Phenom II fixes this by not allowing individual cores to run at clock speeds independently of one another; if one core must run at 3.0GHz, then all four cores will run at 3.0GHz. In practice this is a much better option as you don't run into the situations where Phenom performance is about half what it should be thanks to your applications running on cores that are operating at half speed. In the past you couldn't leave CnQ enabled on a Phenom system and watch an HD movie, but this is no longer true with Phenom II.

Honestly, AMD's initial Phenom approach is more elegant, but unfortunately the current task scheduling mechanism causes problems. The other issue is that Phenom wasn't switching core speeds quickly enough; ideally it shouldn't matter that a high-priority thread got bounced to a new core, as the new core should simply scale up to full speed in a fraction of a second. Regardless, Phenom II addresses the issues with Phenom CnQ performance not being where it should be.

The Phenom II now supports a maximum of four p-states, with a minimum clock speed of 800MHz. The states for each chip are defined below:

Processor Max P-State P2 P3 Min P-State
AMD Phenom II X4 940 3.0GHz 2.3GHz 1.8GHz 800MHz
AMD Phenom II X4 920 2.8GHz 2.1GHz 1.6GHz 800MHz

Intel still has the technological advantage with Core i7; while it too runs all of its cores at the same frequency, idle cores can be turned off completely thanks to the use of Intel's power gate transistors. While this would be nice to have with Phenom II, at least we finally have a working CnQ.

I ran SYSMark 2007 to demonstrate the performance impact of CnQ on Phenom and Phenom II:

Processor SYSMark 2007 Overall Score
CnQ On
SYSMark 2007 Overall
CnQ Off
% Increase When Disabling CnQ
AMD Phenom II X4 940 182 185 1.6%
AMD Phenom 9950BE 136 157 15.4%

Note that the performance on Phenom goes up by over 15% when I disable CnQ, while Phenom II shows less than a 2% gain. This is actually a best case scenario for the original Phenom, however; in my testing I've seen situations where performance is cut in half. Bottom line? The Cool'n'Quiet problems are now resolved, and Phenom II is starting to look recommendable.

Cache and Memory Controller Comparison 45nm and Low Power Consumption
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  • rudolphna - Thursday, January 08, 2009 - link

    Hey anand, do you think you could grill AMD and see if you can get out of them which chips will be made at the upcoming Malta, NY fab facility? Will it be PII or maybe bulldozer? Reply
  • mkruer - Thursday, January 08, 2009 - link

    Anand, I do alot of paring and although the recovery rate is good, i would like to see the results for creating a par2 file. Reply
  • Natfly - Thursday, January 08, 2009 - link

    I'm glad AMD is somewhat competitive in the quad core realm but I just cannot get over how blindingly fast the Core i7s are. It is incredible.

    I hope AMD can make it through, for consumer's (and my stock's) sake. This is a step in the right direction.
    Reply
  • xusaphiss - Thursday, January 08, 2009 - link

    Come on, guys! I like a competitive market as much as the next guy but AMD is a whole generation behind. They should have had these when the 45nm C2s came out!

    AMD is lapped!

    It's time for them to die!

    CPU standards will only go down if they actually resort to third-party distribution!

    Their video cards are always run hotter than NVIDIA and just less stable and overclockable. The only way they was able to stay alive in the race was pitting two of their GPUs against one on one board. NVIDIA hasn't even begun using DDR5 yet!

    Intel and NVIDIA is not really receiving competition from AMD. AMD is just lowering standards.

    Reply
  • ThePooBurner - Saturday, January 10, 2009 - link

    PLAYSTATION THREE is that you? Reply
  • aeternitas - Thursday, January 08, 2009 - link

    We would not of had C2D for years, if not for AMD. Please sit down your logic is flawed. Reply
  • Kroneborge - Thursday, January 08, 2009 - link

    Oh, let's hope AMD doesn't die. Or you can add a couple hundred on to the price of all your favorite Intel processors lol. Reply
  • Genx87 - Thursday, January 08, 2009 - link

    This one is simply not going to cut the butter by the middle of 09. True they are cutting into the Core 2 Duo's performance advantage. It still for the most part falls short. And I didnt see this thing really challange the i7 which will be Intels flagship chip by the end of 09. I dont know about AMD's future chips. But the Phenom needs an arch replacement for AMD to compete with Intel. Reply
  • JakeAMD - Thursday, January 08, 2009 - link

    I would suggest an amazing PC experience is about far more than benchmarks or the performance of one component. Some benchmarks today are at risk of losing relevance to real application performance. For example, performance on 3DMark Vantage scores don’t necessarily translate into a better gaming performance. Also, the CPU-only approach to video processing performance is now thoroughly outmoded, as that should be offloaded to the GPU. The Dragon platform technology is really within the budgets people are affording themselves today and we’re doing a better job of serving the real needs of the PC market today. So I would ask you – Is $1000 or more worth the performance difference?
    Reply
  • Genx87 - Friday, January 09, 2009 - link

    I am looking at these gaming benchmarks which is the most intensive thing I do on my computer. My 180 dollar E8400 is cheaper and faster.

    On the server side the i7 looks more attractive for my virtualization and sql server upgrade project. Where $1000 is pennies on the dollar. Though when you factor in total system cost it is usually not even that much.

    Anyways the i7 will come down in price over the course of 09 as a consumer friendly platform is released and the cost of DDR3 falls as production ramps. So it wont cost 1000 more for an i7 system for long. And I question whether an i7 system costs that much more now.

    Reply

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