Overclocking Lynnfield at Stock Voltage: We're PCIe Limited

Remember the on-die PCIe controller? Yep. It's to blame.

Lynnfield is Intel's first attempt at an on-die PCIe controller and it actually works surprisingly well. There are no performance or compatibility issues.



The on-die PCIe controller needs more voltage as you overclock Lynnfield, limiting Lynnfield's stock vt overclocking potential.

Unfortunately the PCIe controller on Lynnfield is tied to the BCLK. Increase the BCLK to overclock your CPU and you're also increasing the PCIe controller frequency. This doesn't play well with most PCIe cards, so the first rule of thumb is to try and stay at 133MHz multiples when increasing your BCLK.

The second issue is the bigger one. As you increase the BCLK you increase the frequency of the transistors that communicate to the GPU(s) on the PCIe bus. Those transistors have to send data very far (relatively speaking) and very quickly. When you overclock, you're asking even more of them.

We know that Bloomfield can easily hit higher frequencies without increasing the core voltage, so there's no reason to assume that Lynnfield's core cannot (in fact, we know it can). The issue is the PCIe controller; at higher frequencies those "outside facing" transistors need more juice to operate. Unfortunately on Lynnfield rev 1 there doesn't appear to be a way to selectively give the PCIe transistors more voltage, instead you have to up the voltage to the entire processor.

Intel knows the solution to Lynnfield's voltage requirement for overclocking, unfortunately it's not something that can be applied retroactively. Intel could decouple the PCIe controller from BCLK by introducing more PLLs into the chip or, alternatively, tweak the transistors used for the PCIe interface. Either way we can expect this to change in some later rev of the processor. Whether that means we'll see it in the 45nm generation or we'll have to wait until 32nm remains to be seen.

The good news is that Lynnfield can still overclock well. The bad news is that unlike Bloomfield (and Phenom II) you can't just leave the Vcore untouched to get serious increases in frequency.

Overclocking: Great When Overvolted, Otherwise... Final Words
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  • Gary Key - Wednesday, September 9, 2009 - link

    Actually the manufacturers wanted Clarkdale desperately for the school/holiday shopping seasons. It is delayed as they are still debugging the platform, unofficially I think that means the drivers are not ready. ;) Believe me, if we had a stable Clarkdale platform worthy of a preview, you would have read about it already. Reply
  • justme2009 - Wednesday, September 9, 2009 - link

    You are incorrect sir. The manufacturers were complaining to Intel that they couldn't get rid of the current stock before Intel released mobile Nehalem, so Intel caved.

    http://techreport.com/discussions.x/16152">http://techreport.com/discussions.x/16152

    http://www.techspot.com/news/33065-notebook-vendor...">http://www.techspot.com/news/33065-note...-pushing...

    http://www.brighthub.com/computing/hardware/articl...">http://www.brighthub.com/computing/hardware/articl...

    http://gizmodo.com/5123632/notebook-makers-want-in...">http://gizmodo.com/5123632/notebook-mak...o-delay-...

    Needless to say, I'm waiting for mobile Nehalem (clarkdale/arrendale). With a 32nm manufacturing process, plus starting in 2010, Intel will begin to move both the northbridge and southbridge chips onto the processor die. The move should complete some time around 2011 as far as I can tell.
    It will be far better than what we have today, and I'm really ticked off at the manufacturers for holding back progress because of their profit margin.
    Reply
  • Gary Key - Wednesday, September 9, 2009 - link

    I spoke directly with the manufacturers, not unnamed sources. The story is quite different than the rumors that were posted. I will leave it at that until we product for review. Reply
  • justme2009 - Wednesday, September 9, 2009 - link

    Of course the manufacturers wouldn't fess up to it. It's bad business, and it makes them look bad. It already angered a great many people. I don't think they are rumors at all. Reply
  • justme2009 - Wednesday, September 9, 2009 - link

    Personally I'm holding off on buying a new system until the northbridge/southbridge migration to the processor die is complete, ~2 years from now. That will definitely be the time to buy a new system. Reply
  • ClagMaster - Tuesday, September 8, 2009 - link

    “These things are fast and smart with power. Just wait until Nehalem goes below 65W...”

    I surely will Mr Shimpi with this exceptional processor. I am going to wait until the summer of 2010 when prices are the lowest, rebates are the sweetest, before I buy my i7 860. By that time, hopefully, there would be 65W versions available on improved stepping. It’s worth the wait.

    I would wager the on-chip PCIe controller could use some additional optimization which would result in lower power draw for a given frequency.

    Intel sure delivered the goods with Lynnfield.
    Reply
  • cosminliteanu - Tuesday, September 8, 2009 - link

    Well done Anandtech for this article... :) Reply
  • ereavis - Tuesday, September 8, 2009 - link

    great article. Good replies to all the bashing, most seem to have misread.

    Now, we want to see results in AnandTech Bench!
    Reply
  • MODEL3 - Tuesday, September 8, 2009 - link

    Wow, the i5 750 is even better than what i was expecting...

    For the vast, vast majority of the consumers, (not enthusiasts, overclocking guys, etc...) with this processor Intel effectively erased the above 200$ CPU market...

    I hope this move to have the effect to kill their ASP also... (except AMDs...) (not that this will hurt Intel much with so many cash, but it is better than nothing...)


    I see that the structure/composition in this review and in many others tech sites reviews is very good, maybe this time Intel helped more in relation with the past regarding info / photos / diagrams / review guide etc...


    One question that i have (out of the conspiracy book again...) is,
    if the integration of the PCI-Express controller in the CPU die on the mainstream LGA-1156 platform will be a permanent strategy from now on...
    and if the recent delay for the PCI-Express standard 3.0 has a connection with the timing of the launch of mainstream LGA-1156 based CPUs with PCI-Express 3.0 controller integrated...

    Sure, they can launch future LGA-1156 motherboard chipsets with PCI-Express 3.0 controller, but doesn't this contradict the integration strategy that Intel just started with the new processors?
    Reply
  • MODEL3 - Tuesday, September 8, 2009 - link

    I can't edit...
    I just want to clarify that the PCI-Express 3.0 question is for LOL reasons, not taken serious...

    Reply

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