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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  • jnr0077 - Thursday, July 26, 2012 - link

    well i have the better model i5 750 1156 socket gaming score is 5.9 on basic 500 gb hd 7200 with a ssd it hit 7.9 on a gigabyte GA-P55A-UD6 12gb ram. as for the price
    cost was cheep intel (R)quad core (TM) i5 750 @2.66 GHz 2.67GHz cost around £100 mobo cost me £100 i though it is a very cheep upgrade considering price i wood like to here what score any Pehnom II X4 965 hit
    Reply
  • Milleman - Sunday, September 13, 2009 - link

    The article itself is good. But Why on earth compare a standard clocked CPU (AMD) against overclocked ones (Intel). Makes no objective sense att all. I's like having a car test between a standard car and a tuned racecar. Of course the racecar will win in performance. The overclock results shouldn't be there at all. Maybe as a remark that tell what will happen if one would like to overclock. Looks rather unfair and biased.

    So... why??
    Reply
  • Nich0 - Sunday, September 13, 2009 - link

    All I saw in this article is comparison of CPUs in their stock configuration. What's wrong with that? Reply
  • Bozo Galora - Friday, September 11, 2009 - link

    I must say this was a very good logical coherent review with just about all the info one would require

    Good job - I had no intention of getting one of these, but now I may change my mind
    Reply
  • IntelUser2000 - Thursday, September 10, 2009 - link

    http://www.intel.com/support/processors/sb/CS-0299...">http://www.intel.com/support/processors/sb/CS-0299...

    According to Intel...

    Core i7 870:

    5/4/2/2

    Core i7 860:

    5/4/1/1/

    Core i5 750:

    4/4/1/1

    So the i7 870 has higher Turbo mode for 3 and 4 cores than 860 does.
    Reply
  • Nich0 - Friday, September 11, 2009 - link

    Yeah and that means that the OC numbers for the 750 with Turbo don't make sense. For example 4160 / 160 = 26 which would be a Turbo of 6 BCLK.
    Same thing for the 860 OC 3C/4C Turbo number.

    Am I missing something?
    Reply
  • IntelUser2000 - Friday, September 11, 2009 - link

    Its likely Anand has ES versions or such which allows multiplier adjustments. But at stock, the linked speeds are the Turbo Boost grades. Reply
  • Nich0 - Friday, September 11, 2009 - link

    Yeah obviously I am not disputing the stock OC with Turbo enabled (that sounds weird: stock OC?), ie 160*20= 3200, but just what it means in terms of Turbo: it 'should' read 3.36 for 3/4C and 3.84 for 1/2C if the 1/1/4/4 Turbo spec is correct. Reply
  • rdkone - Thursday, September 10, 2009 - link

    I don't like the fact that the BCLK directly and synchronously communicates with PCIe buss, thus affecting the videocard negatively (among other PCIe cards)... This is like overclocking years ago whereas the PCI bus would be affected in the same way and causing headaches... This is a major issue I feel for those wanting to push a fairly big overclock on these CPU's... Intel screwed the pooch for us overclockers I feel... Just more justification to limp along with my core 2 quad at 4.1Ghz rock solid... Like others have said, is funny how the articles don't show older CPU overclocks against all this new garb... In the past they used to... But that hurts sales : ) Reply
  • SnowleopardPC - Thursday, September 10, 2009 - link

    Ok, so what type of boost do I get over a Q6600 with 8gb of ram and windows 7 64?

    Is it worth upgrading or waiting for that 6 core 32nm to come out next year?

    To upgrade to any of these I will need to replace a motherboard and ram with the processor.
    Reply

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