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.
Facebook
Twitter
RSS
343 Comments
View All Comments
JonnyDough - Tuesday, September 8, 2009 - link
Anyone who buys a $1000 CPU has more money than brains. If you wait six months you can buy a newer budget processor for about 1/15 of the cost, overclock it and obtain the same result. I would think that $925 would be more valuable to someone with sense than bragging rights for six months. I was taught that when people brag they are vain morons. A person's value should not be estimated by the stuff they have, but by the choices they make. We all get a lot in life, it's what you do with it that sets you apart. Unfortunately our society is ruled by greed and capitalism. I choose to speak against that. If you have a problem with that, I suggest you take it up with the greedy capitalist complaint department. They don't care either.max347 - Wednesday, September 9, 2009 - link
Hmm, it would seem to me that someone who has $1k to spend on a cpu probably has "alot of brains", hence the better-than-average financial position, enabling the purchase in the first place.Also, you equate greed to capitalism. This is clearly false. People get what they work for in a capitalist society. I am not saying it is perfect, though what would be a better alternative? People are not going to be financially equal, as some work harder than others. To dispute this would demonstrate a lack of experience...to say the least.
Someone chooses to get the best. It's their money, their choice. But you're right, you should probably call them a greedy capitalist.
fullcooler - Wednesday, September 9, 2009 - link
wow, you said that way calmer than I would have. very classy reply to a young leftist. perhaps when obama passes the "free $1000 cpu's for lazy punk leftists" plan, you and I can pay for his cpu,and he wont be a sellout to the man by working for it.imaheadcase - Tuesday, September 8, 2009 - link
I hate people who used that phrase "Has more money than brains". Doesn't it stand to reason, they have brains..if they have more money than you to buy the CPU... lolJNo - Tuesday, September 8, 2009 - link
Not necessarily - they might have inherited the money for example.Maybe you have more money than brains too...
JonnyDough - Tuesday, September 8, 2009 - link
Yep. These people sound like they have no idea how to be frugal with money. It's ok though, a fool and his money are soon parted.lyeoh - Thursday, September 10, 2009 - link
Stop doing that ok?If you discourage too many rich/stupid people from buying the bleeding edge stuff it just makes it harder for the rest of us.
Poor folks like me need those rich guys to rush out and buy the expensive CPUs (and GPUs etc) and work all the bugs out, get the production line ramped up etc.
Then 6-12 months later we have good and cheap stuff to buy.
The best CPU costs way less than an expensive house anyway, so it's not like he's going to cause some sort of nation wide or global financial crisis.
VaultDweller - Tuesday, September 8, 2009 - link
Maybe they don't know how to be frugal with money.Maybe they don't NEED to be frugal with money.
Sure, a fool and his money are soon parted - but so is a brilliant rich man who has more money than he needs.
niva - Tuesday, September 8, 2009 - link
I disagree with your first statement. There are people who simply want the best/fastest and will pay the money for it. Only in the last 3 or 4 years has top of the line performance become relevant only for gaming. A few years ago all sorts of pros needed the fastest they can get their hands on and purchases like $1k per CPU were actually justified.Now just because you can't afford a 1k CPU and never have been, doesn't mean people who buy such things are morons. Same goes for buying a Ferrari by the way. Quit being a jealous putz, thanks!
JonnyDough - Tuesday, September 8, 2009 - link
When you compare value ratios, yes. A $1000 CPU is soon worth about $75. A Ferrari sold as parts is worth about 1/15 of the price also. I didn't think I'd have to spell it out for you.