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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  • Walkeer - Thursday, October 15, 2009 - link

    Super, so because MS Vista has a really bad and stupid CPU scheduler, AMD had to disable perfectly legit and smart power saving feature = CnC per core rather than per chip. I really love windows! I expect that CnC per-core caused no problems under linux for example.... Reply
  • CuE0083 - Sunday, April 26, 2009 - link

    I have been a reader of this site for a few years (first time commenting) and I just wanted to know how you guys determine that a particular processor is a good overclocker.

    1) Do you guys try overclocking multiple chips?
    2) Do you just walk into the store, pick a random chip, and try overclocking it?
    3) Or does AMD send you a chip?
    Reply
  • v12v12 - Thursday, July 23, 2009 - link

    All this bickering and nick picking—when to me the solution seems simple.

    All the poor folks clamoring about numbers they COULD NOT EVER POSSIBLY tell the difference if using Intel Vs AMD in a dboule-blind test! None of you can tell the measurable diffs in FPS and temp. It's all little programs with numbers telling you there's a difference. So wtf is all the fus about?

    Phenom-II is for people that already have an old AM2 rig and want to upgrade. But you forget that your old, slow ass mobo chipset and antiquated ram wouldn't even come close of a newer Intel system period.
    A Brand NEW Phenom-II would "compete," but it barely does that. And as prices drop Phenom-II is losing even more ground as someone with an intel 775 can spring for a fast Quad-core, while you're stuck with the SAME OLD MOBO and RAM DERRRRR?
    Stop all the nit-picking and bemoaning over Intel.

    Does it make sense to scrap your current AMD rig for a completely new Intel unit?

    YES = If you're doing video/AV editing and plan on getting an i7/i5 or if you’re not broke!

    NO = If you currently have an AMD and need some extra horse-power.

    But to falsely rationalize your purchase/mindset by suddenly putting the i7 into the "it's SO expensive" BS category; you're BROKE, you have no say about price. Get a real job and stop spending money on other nonsense and SAVE up like smart people do. It's YOUR own fault you cannot afford a damn $1100-1400 computer: that's NOT a lot. Just b/c YOU cannot afford it doesn't mean there's something "wrong" with i7.

    You're comparing a 2yr old Q6600 against AMD's newest unit LOL? That's like a car magazine comparing the newest lambo to a 2 year old Ferrari etc. BUT PRICE OMG... Prices steadily go DOWN, thus folks with 775 can still upgrade to 6700, 6800 and so forth.

    I'm glad AMD is "sort of" showing a rally to CATCH UP... BUT... when you buy into INTEL you're buying into a PROVEN ROADMAP OF PERFORMANCE VS AMD: you're buying into a mystery grab-bag of performance PROMISES.

    Geesh. Just get the Phenom-II if you cannot afford the i7. Nobody with sense is talking about going from a Q6600/9xxx to 2 year behind the pack Phenom. This is just sophomoric nonsense.

    Common-sense would tell you:

    1) GET A BETTER JOB (education/certs etc)

    2) Stop spending money on other hobbies and misc junk

    3) STFU already and improve your financial situation, THEN you have a say. It's YOUR fault you don't have enough for a paltry $1200 machine. WHO doesn't have $1200? If you don't you haven't EARNED the right to complain. Complain b/c it's someone else's fault - I'm betting it's mostly your own lack of saving & discipline that's the problem.

    None of you may like or agree w/me, but guess what? I don't care b/c I HAVE $1200 to spend so Fsck it I'm happy. Stop drinking, doing drugs, going out, blowing money on cable-TV and crap, for a change? Most of you are guilty of 1 or more of these frivolities.

    Honestly THINK about what you’re saying here? You’re complaining about a superior i7 that is too expensive to do WHAT— play some damn video games? So your rationale is to do what? Buy a new or CPU upgrade to do the same? So THUS instead of continually saving to get the best… You BLOW your loads for inferior technology… and so the cycle continues. You’re NOW BROKE AGAIN and behind. Maybe you’ll start saving once again and come out of the wood work 2-3yrs later and STILL be complain once again “OMG it’s TOO EXPENSIVE” “I’ll by the cheap crap instead!”

    LMFAO NOW THAT IS Ludicrous!
    Reply
  • goofbud - Tuesday, December 06, 2011 - link

    Are you serious dude?

    It ain't the money. I know. I have money. I also have a lambo a porche and an evo. I like testing AMD because they give us "certified" techs something to tinker with and work on. AMD is a brand for builders and true techs like to tinker with a processor and see how far it can go. Even when I was in high school I owned 486's which were the latest and greatest that time. I had an INTEL PC and it sucked dirt once Microsoft came out with windows. Maybe Intel is ahead now but AMD is catching up. They can create the ultimate processor but they don't have to. Not yet.

    BTW, watch how you talk. Be considerate. It ain't the money man. I can afford to buy as many alienware pc's I want. But I don't. Am I a gamer? Yes! I have a powerful system now and am happy I did not spend a lot of money on it. See, this is the thing. If you are smart you just don't want to buy the fastest CPU and fastest RAM that comes out. It's like buying an PS3 for $6,000.00 on ebay just because you want to be the first to play it. That is stupid.

    People buy AMD because they are tweakable. They try to buy the cheapest parts out there, tweak it, and see how far it can go. Makes sense?

    So what if you have the fastest computer in the world. If you don't use it everyday you just wasted money.

    Understand now kid. Now STFU and Go to your room!
    Reply
  • sandstones - Wednesday, March 25, 2009 - link

    I know that we should look at relative sysmark scores, but I'm still puzzled by the higher scores in this batch of tests, compared to those done in April 2008.

    For example the top performer from April - Core 2 Duo E8400 got a score of 161 on Overall in April 2008, and 191 in Jan 2009. The X4 Phenom 9750 went from 126 to 148. Other CPU's in both tests had similar differences. That's a bigger percentage difference than what gets used to debate whether Intel or AMD is better.

    Anand - any comments on what caused such a large difference?
    Reply
  • Amitjakhar - Friday, February 20, 2009 - link

    http://www.overclockersclub.com/reviews/phenomii94...">http://www.overclockersclub.com/reviews/phenomii94...
    After overclocking it really comes near and sometime it gets better performance them Core i7. Which is good. AMD has done superb job and they are in the right direction. Next black edition will make Intel so worry they have to go to work again.
    Reply
  • Amitjakhar - Friday, February 20, 2009 - link

    Phenom II is showing power much better then here. To me it seems they have not done the testing properly. You better check out this link and find how its performing genuinely
    http://www.guru3d.com/article/amd-phenom-ii-x4-920...">http://www.guru3d.com/article/amd-phenom-ii-x4-920...
    Reply
  • salem80 - Tuesday, January 27, 2009 - link

    The Q9400 are 126W~174W not like what Intel said 95W ?
    even E8600 (124W~157W) while they say 65W ?
    their huge deferent in numbers here .
    Reply
  • pcuser123 - Saturday, January 24, 2009 - link

    I think the new i7 core sucks compare Phenom II. Just look at the pricing vs performance on those two.
    Here is the benchmarks http://www.overclockersclub.com/reviews/phenomii94...">http://www.overclockersclub.com/reviews/phenomii94...
    Reply
  • gipper - Monday, January 19, 2009 - link

    You do the overclocks but don't show us the results? Following overclocking, those stock processors have WIDELY different capabilities.

    I'd love to see those video encode charts redone with the overclocked processors. That would tell me the TRUE value of the 64x2BE, C2D, Phenom, PhenomII, and i7 relative to one another.

    Otherwise, your overclock information borders on worthless.
    Reply

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