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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  • Beno - Monday, January 12, 2009 - link

    fanboys help keep them alive.
    if more ppl started looking at AMD again, then Intel will be scared, so us the consumers will be happy because of prices.

    intel has been greedy and overpriced their c2 because there was no competetion at that time.
    Reply
  • garydale - Friday, January 09, 2009 - link

    I generally buy AMD processors for two reasons. The first is that I am not a gamer so I'm looking for cost-effective business application solutions. I'd rather double the memory than increase the processor speed, so AMD works well at the price points I build to.

    Secondly, I believe in the need for competition. With the power PC processor virtually absent from the consumer market and there being little else to choose from for the desktop market, AMD is Intel's only real competitor. So long as AMD has chips that are good enough to compete with Intel's on price/performance, I prefer to buy them.

    If Via got their Cyrix processors up to a decent speed, I might be tempted to switch to them, but let's face it, they don't really compete in this market. So in a two-way race, we need to put our money behind the underdog to prevent a monopoly.

    I've been buying ATI cards too for similar reasons. Nice to see that AMD's making advances in both areas.

    To be clear, I've got nothing against Intel, at least not since the Pentium fiasco, but I think everyone will agree that having multiple firms competing is better for consumers than having one company dominate (Windows 95, 98, Millenium Edition, Vista come to mind). :)
    Reply
  • aeternitas - Friday, January 09, 2009 - link

    Much of your post should go next to the Webster definition of "AMDfanboi"

    If you want true competition, buy the better product. I got my sweet A64. I will now consider P2 over a C2D, but because of price/performance/watt alone.
    Reply
  • Certified partner - Friday, January 09, 2009 - link

    "Blender is one of the few tests that doesn't strongly favor the Core i7, in fact it does not favor them at all. Here the Core 2 Quad Q9650 is the fastest processor, followed by the Phenom II X4 940 and the Phenom II X4 920."
    http://www.techspot.com/review/137-amd-phenom2-x4-...">http://www.techspot.com/review/137-amd-phenom2-x4-...

    "Blender shows Phenom II less competitive than the other 3D rendering tests we've seen thus far."
    http://www.anandtech.com/cpuchipsets/showdoc.aspx?...">http://www.anandtech.com/cpuchipsets/showdoc.aspx?...

    Both can't be true. Explanations would be highly appreciated. I suggest, that anandtech ask techspot about the test settings. Blender is capable of using several threads but I'm not sure wether the optimization is automated. Please, play with the settings. For example, 8*8 (render) tiles can benefit from 8 threads while 1*1 can't.
    Reply
  • Max1 - Friday, January 09, 2009 - link

    How much money has paid Intel to you for this "testing"? You have tested productivity of processors only on two games. In both games productivity of Core 2 is above. In one of them much more above, but it happens seldom. Other tests show, that productivity of Core 2 Quad in part of games is above. In part of games productivity Phenom II of same frequency is above. Why there is so a lot of coding and synthetic tests where Intel is faster, and as always there are no other applications? Why you continue to say lies, as earlier liars for money of Intel that Northwood is ostensibly faster, than Barton. Reply
  • strikeback03 - Friday, January 09, 2009 - link

    I'm surprised how long it took the fanbois to start commenting on this article. Didn't really get rolling until several pages into the comments. Reply
  • JimmiG - Friday, January 09, 2009 - link

    Bit disappointing that it's still slower than Core2 clock for clock. But given the performance of the original Phenom, I think the CPU performs as expected. A big leap for AMD. Unfortunately for them, Intel made an even bigger leap when they switched from Netbust to Core2.

    Also a bit concerned about this supposed "backwards compatibility". Many of the original 790FX boards, my M3A32-MVP Deluxe in particular, will not work with AM3 CPUs because Asus does not plan on releasing a BIOS update. Of course that's the fault of second-rate mobo companies like Asus, and not the fault of AMD. I'll probably end up getting a DDR2 PII-940 to replace my X4 9650, but I'll wait until the prices have dropped some.
    Reply
  • anandtech02148 - Friday, January 09, 2009 - link

    Just wait till Am3 socket comes out, Intel will have to make a slight cheaper version of x58chipset. Is that sweat i see on their forehead?
    Amd buy Via's Nano and give them a 2 prong attack.
    Reply
  • RogueAdmin - Friday, January 09, 2009 - link

    AMD has gone a long way to improving the performance of its processors, and everyone should go out and buy them. They need our support, and without it we will have to put up with whatever Intel decide to give us. And everyone here I think remembers the P4 days, let them not come again!
    The AM2 /2+ /3 platform is by far the easiest upgrade option. No need to worry if your NB chipset supports the latest FSB or RAM, because its all integrated into the CPU. A feature than Intel has copied in its new i7. Along with the monlithic quad core design, and level 3 cache. Also do not forget that AMD released the first x86-64 CPU, and intel basically complied to its x86-64 code to be compatible with the software developed for it.
    i7 is fast, very fast. But do you need that kind of performance in your everyday life? i7 is designed for workstation's hence the benchmarks of video encoding and 3D applications. Gamers would be better off getting a top of the line GPU. Is your CPU 100% utilized 24/7?
    I saw a comment about the 2 year old Core 2 Quad being faster, only in Far Cry 2, that one test. And I would rather play Crysis anyday.
    Since its release Intel has tweaked the performance of these with new cores no end.

    Sorry I digest.... lol

    Keep things competitive, buy AMD. Fanboy or no, let the price wars rage on.

    Reply
  • aeternitas - Friday, January 09, 2009 - link

    1. Most people use their everyday system to *work* too.
    2. Dont compare i7 to P2. Youll just look like youre really reaching and a fanboy.
    3. You dont -Need- anything better than a A64 for everyday tasks. Depending on how long you wanna wait though, you will go to a better system. That point about not -needing- better hardware has always been ridiculous and only applies to grandmas and people that use the computer for browsing and music. Those people dont care about this area in computer so its moot!

    P2 is great, but be realistic. Its competing against C2 right now. Comparing technicalities and -who was firsts- doesnt provide more FPs in anything. It just makes for flame fodder. The numbers speak for themselves and I think this article did a good job in putting the P2 in its place. As a great alternative for people looking to upgrade from older than C2 hardware.
    Reply

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