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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  • TravisChen - Thursday, January 08, 2009 - link

    http://www.anandtech.com/cpuchipsets/showdoc.aspx?...">http://www.anandtech.com/cpuchipsets/showdoc.aspx?...

    What's the system configuration of the Power Consumption test and which software did you run for loading the system?
    Reply
  • Clauzii - Thursday, January 08, 2009 - link

    2009 is going to be very interesting for AMD. The foundry layoff should give them some air to breathe and concentrate on the CPU designs. Reply
  • Skobbolop - Thursday, January 08, 2009 - link

    AM2 support sounds good, but as far i can see very few mobos with AM2 chipset acually supports phenom CPU's... too bad..

    i was hoping that i could upgrade with my MSI K9N Platinum.. :(.. this sucks..
    Reply
  • Thorsson - Thursday, January 08, 2009 - link

    Performance isn't really any better, except in a couple of tests, than C2D chips that are 18 months old, so there's no reason to upgrade for a large chunk of us, and most of the rest will want i7.

    They need a top end chip that compares to the top end i7 like the 4870 was to the GT280. And this is some way from that. It's like the 4870 was competitive to the 9800GT, and was the same price as well.

    With no upgrade path this looks like one strictly for the fanboys at the moment.
    Reply
  • calyth - Friday, January 09, 2009 - link

    Ha. I'm not quite sure whether I hsould try to respond to this, but sure...

    It's a non-trivial task to completely redesign the cores themselves, and I'm not even sure whether they could, say cut out the core, and drop in a new one. It's easy for us sideliners to say they need to improve, and quick, but they need to design a new one that has a much better IPC, with speed, not haste.

    How is this with no upgrade path? This provides an upgrade path for boards up to AM2, which is good enough. With the AM3 versions coming out, people could drop the AM3 version into an AM2/AM2+ board, wait if necessary until DDR3 prices falls some more, and swap to a newer board with DDR3. And now they've a spare computer.

    Look at the i7 prices. Friend of mine just spent 2k for an i7. Sure, he's having fun compiling and playing games with impunity, but I don't think it's the best use of money. Also, C2D is dead. You can't put an i7 into and C2D board, and there's still a good amount of people with older boards that could have a drop in boost.
    Reply
  • Atechie - Thursday, January 08, 2009 - link

    If the CPU had been relased just after Core2, then it might have been a good CPU.
    But today, after 2 years, AMD's "native" quadcore still can beat the Core2 clock for clock...that is more than sad.

    All Intel needs to do now is slash prices of Yorkfield until their i5 socket 1156 dualchannel DDR3 comes out, and they still got AMD by the balls.

    To little, to hyped, to late...
    Reply
  • Sunrise089 - Thursday, January 08, 2009 - link

    This is silly. If the CPU had come out in Summer '06, it would have been god-like. Quad core vs dual-core, higher clock speed, equal or better overclocking, very competitive clock-for-clock, and on a smaller and cooler process.

    What you could say was that if it came out right as Peryn launched it would be a close race...but Peryn improved lots of stuff over Conroe, so it isn't fair to say AMD is 2 years behind.
    Reply
  • Denithor - Thursday, January 08, 2009 - link

    I think that's what Atechie's getting at. Intel took the right path by just cobbling together two dual-core processors to make a quad, while AMD spend excessive time and God only knows how much cash to develop a "monolithic" quad. Which then rolled over and played dead.

    Hopefully AMD has learned from its mistakes. Otherwise Intel may not have much competition in the near future. What's AMD trading at again, these days?
    Reply
  • Proteusza - Thursday, January 08, 2009 - link

    I dont know, this doesnt do it for me. I'm a massive AMD fan - I run a 5600+ right now, my previous CPU was an XP 2400+.

    What is it now, 2 years since the Core 2 Duo was released? And AMD still cant match in clock for clock performance? After the monumental flop that was Phenom, massive delays, poor performance, high power consumption, the TLB bug, patchy backwards compatibility (my MSI K9N mobo with the Nforce 570 SLI chipset cant run AM2+ chips, but the equivalent Asus can), they launch the Phenom II, and the best I can say about it is that is that its acceptable. Acceptable. Not Phenomenal. Just acceptable. Price vs Performance wise, it gets the job done, mostly, sort of. Throw newer game engines at it and even the Q9600, that old workhouse, can beat it.

    Its not that Phenom II is a terrible processor. Its not. Its just not what I expected AMD to launch, many months after the flop that was Phenom. I expected something that could at least beat a 65nm Core 2 Duo, if not a Nehalem.

    As Anand hinted at, Intel is going to drop prices, which they can afford to, forcing AMD to do likewise, which they cant. AMD's die size is similar yet their margins are far smaller. Intel's next CPU will be the die shrink of Nehalem, what will AMD release? Will it even match Penryn? I can only hope.
    Reply
  • KikassAssassin - Thursday, January 08, 2009 - link

    Since the Phenom II was always known to just be a die shrink with some optimizations, you were setting your hopes way too high if you thought it was going to compete directly with the i7. AMD needed this launch to keep them in the game, and it looks like it's probably just good enough to be able to do that. We probably won't be seeing any big breakthroughs from AMD until Bulldozer, so we just have to hope that this architecture will have enough headroom in it to last that long. Reply

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