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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  • Shadowmaster625 - Friday, January 16, 2009 - link

    Why didnt you include an overclocked E5200 in the testing?!?!?!

    omg this is horrid. How do these $230-$270 CPUs compare to an $85 E5200 coupled with a $105 Gigabyte GA-EP45-UD3R? That combo will easily overclock to 3.8 Ghz on stock cooling. CPU, mobo + RAM all for less than the cost of a Phenom II. And better performance too.
    Reply
  • Reynod - Monday, January 12, 2009 - link

    Another excellent article Anand.

    Would you be able to write a short piece on the AM3 socket and the "likely" impact on performance once you have some samples please?

    Reply
  • R4F43LZiN - Saturday, January 10, 2009 - link

    I wanted to see some Phenom II overclocked gaming benchmarks... Reply
  • zagortenay - Saturday, January 10, 2009 - link

    To correct my mistake in above post:
    "And check the link of very respectable "Guru of 3D" yourself, X4 940 beats Core i7 920 in higher resolutions." Not Core i7 940.
    Reply
  • zagortenay - Saturday, January 10, 2009 - link

    Great comments Aranthos! AMD did a great job with Phenom II, no doubt about that.
    Anandtech review is kind of fair and balanced when it comes to giving the final verdict, but the tests are deceiving and unfair as usual.
    First of all, as somebody else has already pointed out, they used an average mobo to test Phenom II, while they used expensive enthusiast level mobos for Core2 Quad and Core i7 (230 and 250 Dollars respectively). They could not find an Asus M3A79-T (which is much cheaper at 185$) There is no excuse for that! Either a deliberate move not to show what Phenom II can deliver at its best, or Anand needs to learn a lot from us. Just check the below link to see the performance difference between 790GX and 790FX. Quite some performance difference in some benchmarks and consider that it is still a close competition with an average AMD motherboard.
    There IS a difference apparently: http://www.legitreviews.com/article/795/5/">http://www.legitreviews.com/article/795/5/ and it would change some conclusions
    And now introducing a classic: Why Core2 Quads run on DDR3 (Yeah, all Core2 Quad users definitely switched to DDR3, lol!) and Phenom IIs run on DDR2? To show the best of Core 2 Quads... So what happens if DDR2 is used also on Core 2 Quads? See yourself below. X4 940 beats Q9550 most of the time and even Q9650 in some applications.
    http://www.bit-tech.net/hardware/2009/01/08/amd-ph...">http://www.bit-tech.net/hardware/2009/0.../amd-phe...
    I wander what trick they will do with RAMs, when Phenom II AM3 (with DDR3) comes this February.
    Anand says X4 940 trails Q9650 and by 28.4% when it comes to Far Cry 2. Is it so? Or? Check the above link again. Even with DDR3 RAMs Q9650 leads by only 4.4%. With DDR2, X4 940 leads this time, with a little margin. Same resolution! Who to beleive?
    And check the link of very respectable "Guru of 3D" yourself, X4 940 beats Core i7 940 in higher resolutions. He he!
    http://www.guru3d.com/article/amd-phenom-ii-x4-920...">http://www.guru3d.com/article/amd-phenom-ii-x4-920...
    So what? Don't get fooled, don't get deceived by the "big brother connections".
    Final words: Yes I am a fan boy and I don't pay a penny for Intel!
    Reply
  • Aranthos - Saturday, January 10, 2009 - link

    I wonder why so many people keep saying "What happened to the AMD from the Athlon64 era? It was whupping Intel!" etc.

    That AMD is still here. The same AMD that so long ago brought us Hypertransport, the integrated memory controller, native dual-core and the like brought us native quad-core and a three level cache heirarchy a full year before Intel did either. As it turned out, Intel did it better - a fact with which I won't even try to argue. However, AMD is still working.

    P1 flopped. It was the most hyped chip in years, and brought all sorts of false promises. All Deneb promised was better overclocking, lower power consumption and more clock-for-clock performance. It did all 3.

    I'm not going to say Intel ripped off AMD by using an IMC and a HT-esque high speed interconnect. Granted, AMD did it first, but Intel would have ended up doing it ANYWAY because it is a good idea.

    Back to the original topic - we still have the old AMD with us. They're still innovating as always. But, we have a new Intel. One that isn't peddling crappy Netburst chips. New Intel is going out guns blazing, and they have the money to make sure that another P4 doesn't happen.

    AMD got lucky back in the P3 -> P4 era. They're gonna have to either pull out a win of epic proportions, or stick to razor thin margins on their chips. Intel has seriously deep pockets, and can easily afford to destroy AMD's prices.

    i7 is epic win. But I'm buying a Deneb anyway. Yeah, people are gonna call me a fanboy, and so what. I'm buying a chip made by a company that is facing a company over 50x their size. While they're not a little family run business, I will support them to their dying breath because they need every sale they can get. I like high performance as much as the next guy, but if buying higher performance (in my case at a higher price [I have an AM2+ motherboard]) puts the business a step closer to being one-sided, then Intel can suck it. They don't need my money.
    Reply
  • Mathos - Saturday, January 10, 2009 - link

    Well, it's not quite a 4800 series equivelent release this time. More like being around the same as the 3800 series was. A good improvement over the hd2000 series cards, in this case a good improvement over the phenom 1.

    On the other hand I am wanting to see what will happen with the AM3 versions. Should improve scores quite a bit on anything that likes memory speed and bandwidth. I'm also wondering what other optimizations will come with AM3. Gonna wait for that, since I should be getting another nice quarterly bonus around the time those come out. Use a pII 945 on my old k9a2 plat till I can get an AM3 board and DDR3 memory.
    Reply
  • Maroon - Saturday, January 10, 2009 - link

    This was a great step forward by AMD. After the Phenom flop they had to transition successfully to 45nm or basically fold. They have done that. AMD doesn't have the resources to compete with Intel on the highend right now, but with this release they can compete in the mainstream market where most processors are sold.

    They're using the same strat that worked for the 4xxx series video cards, performance per dollar.

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

    Have the Intel fanboys noticed that they're comparing a DDR 2 Phenom II to a DDR 3 i7? I know AMD will be slower anyway, but it should close the gap a bit, right? Reply
  • aeternitas - Friday, January 09, 2009 - link

    Are you serious? DDR3 might be able to give AMD an advantage overall compared to the C2. But then going DD3 and spending that much money, you might as well go i7 anyway. (unless you're a fanboy)

    Seriously guys, if you're going t go around comparing P2 to the i7, you need to focus on price! Else you'll look really bad.

    P2 is against C2. End of story. You cant sit around theorizing some magical item is going to get a P2 anywhere close to the i7.

    Stop defending AMD. They have 18 months of catchup to do and dont need pats on the back and excuses from people like you. They have a good chip and alot of good things in the chip that they dont need to do in the future as they come up with new architecture.
    Reply

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