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
POST A COMMENT

343 Comments

View All Comments

  • Supershanks - Thursday, September 10, 2009 - link

    Great Article Anand, I read it with great interest.
    However I found somthing that was strange and unexpected today
    My I7-860 was running at 30x133 3990 when running nucleus, that's according to cPU-z I have a link , but can't post http in this comment ?
    http://www.clunk.org.uk/forums/reviews/24295-asus-...">http://www.clunk.org.uk/forums/reviews/...-deluxe-...

    I'd appreciate your insight ?
    thanks
    Reply
  • Gary Key - Thursday, September 10, 2009 - link

    You need to change your version of CPU-Z. I have a screenshot somewhere around here of 48x133. ;) Reply
  • Scali - Thursday, September 10, 2009 - link

    On a slightly related note... With these new P55 boards I see that especially Asus uses a new line of onboard audio chips from VIA.
    I haven't really been able to find much info on these chips. I'd like to know how they compare to Realtek and other onboard offerings.
    Could you guys spend some time on reviewing the onboard audio next time you review one of these boards? Eg, what does the control panel for these chips look like, what features does it have (eg, can you have realtime encoding like DTS connect or DD Live?), what is the general driver quality like (proper support of 3d/eax effects etc)?

    I think that's what's been missing in general, the past few years. Onboard audio has gotten quite advanced, to the point where most people no longer use a separate soundcard (some boards actually come with some sort of X-Fi card). However, I rarely see onboard audio reviewed, only audio cards.
    Reply
  • agawtrip - Thursday, September 10, 2009 - link

    for me, i find this review is misleading if you are not a gamer - for i5-750 and PII x4 965.

    why?

    1. motherboard and video card - non-gamer dont buy sli/xfire board. onboard graphics is fine(780g/785g). for now, boards for i5 setup doesn't have onboard graphics. what will you do? you will be forced to buy a video card (maybe 4550/9400gt for $40).

    i5-750 - $195, GIGABYTE GA-P55M-UD4 - $150, nvidi 9400gt - $40
    --- TOTAL -------- $385

    PII x4 965 - $245, GIGABYTE GA-MA785GMT-UD2H - $90, no video card
    --- TOTAL -------- $335

    AMD setup is actually cheaper but slower. it's all up to you.

    2. power consumption - since you are forced to buy video card, it will consume additional power while AMD setup (780/785G) won't.

    well that's just my opinion.
    please inform me and the others if i given up wrong informatin
    Reply
  • chrnochime - Thursday, September 10, 2009 - link

    Or you can get a motherboard that's quite a bit cheaper:


    MSI P55-CD53

    http://www.newegg.com/Product/Product.aspx?Item=N8...">http://www.newegg.com/Product/Product.aspx?Item=N8...

    which is 120..

    or

    GIGABYTE GA-P55M-UD2

    http://www.newegg.com/Product/Product.aspx?Item=N8...">http://www.newegg.com/Product/Product.aspx?Item=N8...

    And yes I know these are NE prices, and that it might be more expensive/cheaper somewhere else
    Reply
  • Hrel - Wednesday, September 9, 2009 - link

    It DOES NOT have hyperthreading. Enabling it wouldn't increase the cost of the chip, it purely a political move. I HATE that! If a CPU maker has something that can increase the performance of my cpu, at no cost to them, then should enable it, at no cost to me. EVERY CPU should have unlocked multipliers. EVERY CPU should have hyperthreading. Reply
  • jnr0077 - Friday, July 27, 2012 - link

    hyperthreading steal ram from your pc i have a i5 750 + radeon hd 4850 it plays crysis 2 maxed the witcher 2 maxed skyrim maxed i think you need to read up on it before you comment :) Reply
  • PhilTaylor - Wednesday, September 9, 2009 - link

    FSX is well known as a CPU-limited game, it might be more interesting to test it then a GPU limited game like Crysis. For instance, the difference between 2 and 3 memory channels might have a greater impact on FSX, again due to its CPU-limited nature. Reply
  • cactusdog - Wednesday, September 9, 2009 - link

    A very good, detailed bunch of tests but there is a surprising lack of information regarding temps? Other review sites have done the same thing but there IS temp issues with these CPUs as with i7 1366 ones. That CPU at 4.0 Ghz on air will be around 90 degrees but little is said.

    Anandtech is more honest than most review sites (most of which are really just advertisements) but sometimes i get the impression that nobody wants to upset Intel.

    Reply
  • araczynski - Wednesday, September 9, 2009 - link

    ...bottom line to me, my E8500/crossfire setup still has plenty of gaming life left. I'll check back in a year. Reply

Log in

Don't have an account? Sign up now