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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jonup - Tuesday, September 8, 2009 - link
Unfortunately people in corporate world do not make a difference between a HD4500 and a GX790. As lond as the Intel can display spreadsheets its good enough (or better) than a GTX295/HD4890X2, because it is Intel. You can change ignorance when it works.PassingBy - Tuesday, September 8, 2009 - link
My horizons are broad enough, thank you. The needs of many corporate desktops/laptops will be met by Clarkdale/Arrandale and no, nobody will go blind or suffer eyestrain (by virtue of the IGP anyway).PassingBy - Tuesday, September 8, 2009 - link
No edit function, so, as I point out later in the thread, people reading this review presumably won't be interested in IGPs anyway, given that these processors now have no IGP market. Wait for Clarkdale before trying to compare IGPs.dragunover - Tuesday, September 8, 2009 - link
Thanks for the review, if not as soon as I wanted it!Boobs McGee - Tuesday, September 8, 2009 - link
Do you guys have plans to do a motherboard review roundup for P55?If not, please do.
Gary Key - Tuesday, September 8, 2009 - link
I actually have three roundups planned, we have 15 boards here ranging from the $100 uATX items up to the $300 EVGA Classified series. We are only testing with retail products, released BIOS', and retail processors so the delivery of more than 70% of the boards late last week has created a small logjam. ;)The first article should be up on Thursday with a couple of my favorite boards and then a rather large one up on Monday and the last one a few days after that. Raja is working on a separate roundup of the top three boards targeted for the more extreme OC community. We will also have a P55 memory specific article shortly.
ClagMaster - Tuesday, September 8, 2009 - link
Looking forward to reading these P55 motherboard roundups.Anand Lal Shimpi - Tuesday, September 8, 2009 - link
Yes, Gary is nearly complete with his. Give him another day and it'll be up :)Take care,
Anand
Comdrpopnfresh - Tuesday, September 8, 2009 - link
By creating a new socket- they're providing a disincentive for early adopters of bloomfield. This chip is literally a humpty-dumpty that stands to benefit intel with everyone suffering a small loss of their own. The benefits of lynnfield vs bloomfield come from shuffling the architectural deck of nehalem. In reality, it only shows the possibilities of an inflexible architecture.The turbo mode isn't cutting it in day-to-day power consumption reduction. On the scale of a day, the average shmoe who is ass enough to leave a computer on for no reason gains no benefit. Lower the reach of a voltage plane, and reduce the number of components sucking juice, that only present benefits under certain situations (a third memory channel), and shmoe is happier.
If it was in the article, I apologize, but with the pci-e controller being on the un-core... what happens on a chipset with integrated graphics? Will the igp be linked to the processor now, rather than a bridge chip? If ati or nvidia made their own supporting chipsets with an igp- would the igp represent a chip onto itself, solely connected to the cpu, or would it have to work through dmi, and leave those on-die pci-e lanes for domestic usage?
It seems this is the warning rattle to nvidia that they chose their place with ion, and are stuck in it. When the change to 32nm comes, and the gpu is integrated into the cpu- what kind of robust 3rd party chipsets could exist in the budget end? Sure, you can always add a dedicated, off-die, gpu... but for budget boards used to eons of making room for a cpu and working a bridge chip around an igp- either horrible inefficiencies will creep up, or higher prices.
My money is on westmere having at least three power planes.
I'd like to know: with the pci-e controller on-die now... what impact this puts on graphics cards with higher on-card memory. Does it strengthen or minimalize it?
And, can the cpu now share the gpu's memory as a way to extend cache- after years of being forced to share the system pool. That 16gb/s link to gddr5 looks mouthwatering. I'd like to see performance tests run with the pci-e varient ssds floating around out there saddled to the on-die pci-e lanes, and a graphics card running off of chipset. Rather than elevating a horse-power driven graphics subsystem, I think the benefits of supplying more 'torque' by freeing mass storage ssds from the SATA interface would be far more substantial, and in all applications of the PC. You already have the means for nearly 2+2/3 times the theoretical bandwidth of SATA-6- which up til now seems rather bug-ridden and defunct.
Also interested in the outcomes of usb3 with this- as usb is built on the foundations of pci-e, is it not? If usb3 can allow for pci-e externally, and you remove the latency issue of usb signaling traveling from some peripheral bridge chip to the cpu, and just jack the usb3 communications into the cpu... could one use usb3 as a computer-to-computer psuedo qpi teaming/networking bridge for inter-desktop cpu communication. skip the entire bottleneck of client-level software implementation, and the subsystem communication buses for out-of-box signaling too...
plague911 - Tuesday, September 8, 2009 - link
The market just got a little more crowded so hopefully this will bring a reduction in prices of the 920. but..
“The Core i7 870 gets close enough to the Core i7 975 that I'm having a hard time justifying the LGA-1366 platform at all. As I see it, LGA-1366 has a few advantages:
1) High-end multi-GPU Performance
2) Stock Voltage Overclocking
3) Future support for 6-core Gulftown CPUs
“
Your exactly right 1366 I think is going to be be the best option to “future proof” my system however the new chips make the 920- seem a little low on features. With the goal of “performance on a budget” I feel like we are stuck either getting a board with a socket which wont compete in the future, or chip which is weaker than its lower class cousins. Unfortunately I dont see any of this being fixed in the next few cycles. Id like to see a low clocked gulftown (to save cost) feature rich with good OC potential thats on the lower end of the price scale. To me this would be a good follow up to 920 but but it dosent seem like that will be coming out for several cycles. Unless ofc i'm missing something which is probably the case.