New Stuff: Power Management

At this year’s IDF the biggest Nehalem disclosures had to do with power management.

Nehalem’s design was actually changed on a fairly fundamental level compared to previous microprocessors. Dynamic domino logic was used extensively in microprocessors like the Pentium 4 and IBM’s Cell processor in order to drive clock speeds up. With Nehalem, Intel has removed all domino logic and moved back to an entirely static CMOS design.

Nehalem’s architects spent over 1 million transistors on including a microcontroller on-die called the Power Control Unit (PCU). That’s around the transistor budget of Intel’s 486 microprocessor, just spent on managing power. The PCU has its own embedded firmware and takes inputs on temperature, current, power and OS requests.

Each Nehalem core gets its own PLL, so each core can be clocked independently - much like AMD’s Phenom processor. Also like Phenom, each core runs off of the same core voltage - the difference between Nehalem and Phenom however is Intel’s use of integrated power gates.

Through close cooperation between Nehalem’s architects and Intel’s manufacturing engineers, Intel managed to manufacture a very particular material that could act as a power gate between the voltage source being fed to a core, and the core itself.

The benefit is that while still using a single power plane/core voltage, individual Nehalem cores can be completely (nearly) shut off when they are in deep sleep states. Currently in a multi-core CPU (AMD or Intel), all cores need to run at the same voltage, which means that leakage power on idle cores is still high just because there’s one or more active cores in the CPU.

Nehalem’s power gates allow one or more cores to be operating in an active state at a nominal voltage, while remaining idle cores can have power completely shut off to them - without resorting to multiple power planes, which would drive up motherboard costs and complexity.

The other benefit of doing this power management on-die is that the voltage ramp up/down time is significantly faster than conventional, off-die, methods. Fast voltage switching allows for more efficient power management.

I mentioned earlier that the PCU monitors OS performance state requests, so it can actually make intelligent decisions about what power/performance state to go into, despite what the OS is telling it. There are some situations where Vista (or any other OS) running an application with a high level of interrupts will keep telling the CPU to go into a low power idle state, only to wake it up very shortly thereafter. Nehalem’s PCU can monitor for these sorts of situations and attempt to more intelligently decide what power/performance states it will instruct the CPU to go into, regardless of what the OS thinks it wants.

Integrated Memory Controller Turbo Mode


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  • steveyballme - Monday, November 3, 2008 - link

    All you really need to know is that it was designed to run Vista only!">
  • rflcptr - Wednesday, September 24, 2008 - link

    The origin of Turbo Mode isn't Penryn, but rather Intel's DAT first found in the Santa Rosa mobile chipset, of which both Merom and Penryn were compatible (and functioning with the tech activated). Reply
  • hoohoo - Wednesday, September 10, 2008 - link

    Outside of games the only area where raw performance matters to me is running high performance code - for me this is graphics processing and 3D rendering code, and it's just a hobby. I have some dealings with the HPC crowd though.

    In the HPC biz memory bandwidth is a big issue. AMD has won hands down on that metric against Intel until perhaps the past six months. Nehalem server chip looks like it will beat Opteron on this metric.

    Another important metric for HPC is linear algebra performance. GPUs are very good at linear algebra, but GPUs have strange programming requirements for the people who understand scientific programming - these people want to worry about the science or engineering and not about the specific cache architecture of an Nvidia or ATI GPU.

    Just because I could, last winter I wrote some 2D graphics processing routines for an 8800GT+CUDA+AthlonX2-5200: gaussian blur, sharp filter, the like. I achieved on the order of 20x speed improvement on the 8800GT vs the AthlonX2 all on Linux - but it was a moderately brutal programming experience and I doubt your average researcher will do it. And, well, the PCIe bandwidth bottleneck would be a problem for large scale batch processing for such a simple calculation.

    I don't know about ATI GPUs yet. I got a 3870 eight months ago and installed the AMD HPC GPU SDK ('nuff acromyms for ya?), but I can't face the pain of using it if after booting all the way into XP I could be fragging away in HL2 or Q4, or conquering the world in Civ2 Gold instead - and nobody really uses Windows servers for HPC clusters anyway. I think about write Brook+ code on my 3870 sometimes but honestly I don't care that much. It'll be similar performance to the 8800, and it'll be *Windows* code.

    If Intel can produce a chip that is somewhere between Larabee and Nehalem, matching memory bandwidth with an easily programmed but highly parallel chip then Intel will have an opportunity to define a new sub-market: HPC processors.

    It is indicative of the deficiencies of AMD marketing that it has a good GPGPU and the only way to program it is on the one OS that HPC shies away from: Windows. Clusters mostly run on Linux or UNIX.

    But, AMD is working on a CPU+GPU product that could compete in that market.

    Which of AMD or Intel will realize that there is money to be made with a chip that combines 2 or 4 CPU cores + 4 or 8 GPU style linear algebra cores, all with IEEE double precision ability?

    Whither the Cell?

  • hooflung - Monday, November 3, 2008 - link

    I think you are minimizing what an operating system is. While it is true that Linux, AIX and Solaris account for a large number of HPC and cluster environments that doesn't mean Windows is poor in this regard.

    There are solid options for windows HPC where infiniband is very, very solid. Microsoft helped define the spec. However, it isn't done often enough in the public's eye like Linux. Remember, AIX and Windows were the most solid platforms for J2EE for a long, long time.

    Also, Windows Clusters can be the better TCO solution for people. EVE-Online used Windows 2000 (now 2003 x86 and x64 ) and wrote their own load balancing software in Stackless ( and now have their own async IO stackless library ) which holds 33k at any given time of the day.

    You really just have to decide what market you are trying to reach when considering OS choices. They all can provide similar performance.

  • Pixy - Friday, September 5, 2008 - link

    All this sounds nice... but I have a question: when will laptops become fanless? The CPU is fast enough, work on turning down the heat! Reply
  • Davinchy - Tuesday, August 26, 2008 - link

    I thought I read somewhere that if the other processor cores where not working then they shut down and the one that was working got more juice and overclocked.. So wouldn't that suggest that for the average consumer This chip will game much faster than a penryn?

    Dunno Maybe I read it wrong
  • jediknight - Sunday, August 24, 2008 - link

    For desktop builders.
    My aging S754 Athlon64 is dying.. so it's time to start thinking of building a new one. My laptop can only hold me out for so long, though..

    Will I be able to buy a quad-core Nehalem processor in about the $250-300 range by the end of the year?
  • UnlimitedInternets36 - Saturday, August 23, 2008 - link

    Core i7 wins big time for 3D rendering, modeling, and CAD programs.

    Turbo is the best feature. I hope, at least in the Extreme Edition we can set the Turbo headroom to like 5Ghz!!! and have a totally dynamic over-clock scaling FTW!

    Zbrush can utilize 256 processors, so I think a 2 socket Core i7 will help me out just fine. Sure is don't automatic boost FPS in games, but but that's partially a programming issue as well. Sooner or later the coding will catch up.
  • munyaka - Friday, August 22, 2008 - link

    I have always stuck with amd but this is the final Nail in the coffin. Reply
  • X1REME - Friday, August 22, 2008 - link

    Is there anything you see that we don't, please explain why? Reply

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