Intel's Core i7 870 & i5 750, Lynnfield: Harder, Better, Faster Stronger
by Anand Lal Shimpi on September 8, 2009 12:00 AM EST- Posted in
- CPUs
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.
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snakeoil - Tuesday, September 8, 2009 - link
and the cherry on top of the piecore i5 750 and core i3 don't support virtualization.
http://www.virtualization.info/2009/07/intel-core-...">http://www.virtualization.info/2009/07/intel-core-......
that's fantastic, colossal intel.
what's wrong with intel
Anand Lal Shimpi - Tuesday, September 8, 2009 - link
Intel VT-x is supported by the Core i5 750:http://processorfinder.intel.com/details.aspx?sSpe...">http://processorfinder.intel.com/details.aspx?sSpe...
Take care,
Anand
snakeoil - Tuesday, September 8, 2009 - link
sorry incomplete linkhttp://www.virtualization.info/2009/07/intel-core-...">http://www.virtualization.info/2009/07/...core-i3-...
AssBall - Tuesday, September 8, 2009 - link
What are you talking about? These overclock FINE; read the article. 4 Ghz. Anyone that is gonna overclock bloomfield or lynnfield seriously is opting for an aftermarket HSF, so don't bother arguing that. Your comment doesn't make any sense.TA152H - Tuesday, September 8, 2009 - link
You missed the point.When you overclock the processors, you change the characteristics of turbo mode. Consequently, the big advantage of the Lynnfield disappears, and they run at the same clock speed, instead of the Lynnfield at a higher clock speed.
Do you understand now?
eternalfantasy - Tuesday, September 8, 2009 - link
lolemogoinginstyle - Tuesday, September 8, 2009 - link
"There are better sites that have answered these questions. I used to like this site, but this review is another disappointment. "Just how is that Tom's Hardware gig working out for you? I noticed your name was not on any of their launch reviews since you seem to be an expert on the subject. Why is that?
TA152H - Tuesday, September 8, 2009 - link
Thanks for asking.When I have time, I will be writing another article, which they hopefully will use, but to be honest, the time it takes to write an article, at least a well-written one, takes an enormous amount of time and effort.
Getting and verifying data is only part of it. Writing it in an artistic an interesting way is very time consuming, and, at least for me, requires many rewrites of the same pages. Each page took me at least five hours, some many more, plus the upfront time of deciding which pages to write, which probably took at least 30 hours of research.
The editor of Tom's wrote their articles, and it's clear to see the much more thorough review he did. Personally, I like him and occasionally do communicate with him, and I probably would like Anand too, since he seems like a good fellow, but I have no real affiliation with their site. If I write an article they like, they might publish it. That's it.
But, honestly, if you do it for money, you're a fool. It takes WAY too much time for that. You really have to want to do it, and the money is secondary.
goinginstyle - Tuesday, September 8, 2009 - link
So it took you five hours a page to do a copy and paste from Wikipedia on that so called article of yours? I read the Tom's P55 article, not seeing how it was any more thoughtful than the one here or at Tech Report. At least Anand did some searching and reported on items like PCIe clocking/voltage requirements that I noticed was not mentioned at Toms.Your only motive for these posts is to try and look impressive at Toms in hopes that they will publish another boring piece of dung from you. Otherwise, your complaints here are just as justified at Toms or TR, yet you are not posting at either site. That is why it is so obvious as to what you are up to with the flame bait comments.
TA152H - Tuesday, September 8, 2009 - link
I never even looked at Wikipedia, since I don't consider it a valid source of information.Why do you talk about things you don't know about. In fact, some people used Wikipedia to argue some points with me. I made a point never to look at those pages.
But again, what have you done with your, except produce carbon dioxide and speed up global warming? You seem pretty worthless to me.