The Lynnfield Preview: Rumblings of Revengeby Anand Lal Shimpi on May 29, 2009 1:00 PM EST
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Lynnfield’s Secret? Turbo Mode
The current Core i7 runs at a multiple of its BCLK, which is 133MHz. The Core i7-920 runs at 20x BCLK (2.66GHz) while the i7-965 runs at 24x BCLK (3.2GHz). If the chip isn’t running anywhere near its max TDP, the i7 will overclock itself by one speed bin (133MHz). Now say you’re running a single-threaded application that’s got only one core active, if the chip is cool enough the i7 will overclock itself by two speed bins (266MHz).
Turbo mode on the i7 works well and as I found is generally responsible for a 3 - 4% increase in performance. Despite its benefits, the i7’s Turbo mode is very conservative. Our own overclocking tests show that i7s have no problems running at up to 3.8GHz without any additional cooling or voltage, even with all four cores under full load. Given that it was Intel’s first Nehalem architecture, I can understand the hesitation not to go crazy with turbo.
The second version of Intel’s Nehalem turbo mode came with the high end Nehalem Xeon processors. While the single-socket processors worked just like the desktop i7s, the higher end dual-socket Xeons can turbo up more aggressively.
The Xeon E5520, E5530 and E5540 can all boost their clocks by one bin if 3 or 4 cores are active, but two bins if 1 or 2 are active. The X5000 series gets even more aggressive; with 3 or 4 cores active the chips can overclock themselves by up to 266MHz, and if 1 or 2 cores are active they can turbo up an additional 400MHz.
Lynnfield marks Intel’s third generation Nehalem turbo and is correspondingly more awesome.
The leaked roadmaps show that the two higher end Lynnfields can turbo up to five bins, or 667MHz while the entry level Lynnfield can turbo up to four bins (533MHz). I’m guessing this is for a single active core, but what about when more than one core is active? The table below has the turbo specs for the Xeon X5570 (95W TDP), the Core i7-940 (130W TDP) and my guesstimates for the 2.93GHz Lynnfield (95W TDP):
|Processor||Clock Speed||Max Turbo|
|4 Cores Active||3 Cores Active||2 Cores Active||1 Core Active|
|Intel Xeon X5570||2.93GHz||3.2GHz||3.2GHz||3.33GHz||3.33GHz|
|Intel Core i7-940||2.93GHz||3.06GHz||3.06GHz||3.06GHz||3.2GHz|
|Intel Lynnfield ESTIMATE||2.93GHz||3.2GHz||3.2GHz||3.60GHz||3.60GHz|
Given the similarity in clock speed and TDP to Intel's Xeon X5570, I'm guessing the 2.93GHz Lynnfield will follow the same 2/2/3/3 turbo pattern as the Xeon. The higher max turbo frequency means that we'll at least see 3.60GHz with only 1 core active and I'm not really sure what will happen if two cores are active; if Intel follows the Xeon pattern then we'll see 3.6GHz as well, but we may very well see 3.33GHz or 3.46GHz instead when only two cores are active.
Either way a quad-core Lynnfield, thanks to its aggressive turbo mode, will end up delivering good performance regardless of the number of concurrent threads. Forget about it being a quad-core CPU and just think of it as a CPU that will perform as best as possible given its 95W thermal envelope. This, my friends, is the future of multi-core processors. It doesn't matter how many cores you have, just view them as execution resources; if you only need two powerful cores, that's what you get, and if you need to run 8 threads then that's what you'll get. Imagine what we'll get on the 4th or 5th generation of turbo modes.
To those who are wondering why Lynnfield even makes sense, I believe its turbo mode will be its saving grace. I'm more puzzled by the i7-920 at this point.
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Seramics - Sunday, May 31, 2009 - linkWhy is it that in test that demand intensive multi threading, the lynnfield loses out to bloomfield while in less intensive multithreaded or single threaded test, the lynnfield can equal bloomfield? Could it be that in intensive multithreading processing that work up more than 4 threads (thereby requiring the use of HT for better performance), it is able to use the extra memory bandwith provided by triple channel in the bloomfield platform? Maybe in situation where the software can really demand mutlple threading processing intensively, the bloomfield extra memory bandwith provide an edge. An easy way to test this is increasing the memory bandwith of lynnfield and/or decreasing memory bandwith of bloomfield n see wht happens in intensive multithreaded test. Im suspicious of this. Let me know wht u guys thinks.
IntelUser2000 - Sunday, May 31, 2009 - linkThe Turbo Modes for revealed for Lynnfield way before even Core i7's release.
1 core: +5(+4 for non-HT version)
2 core: +3
4 core: +1
It may or may not be coincidence, but the Turbo speed of the highest clock Lynnfield is equal to the Turbo speed of the highest Core i7. The point is, I think since people will overclock the "enthusiast" i7's anyway, the Turbo doesn't need to be so high.
According to Intel, the benefits will be GREATER on smaller form factors, which means laptops will have even HIGHER increases.
RagingDragon - Sunday, May 31, 2009 - linkHmmm... I'm not sure how much sense Lynnfield will make in the long term - at the high end you'll have Bloomfield on LGA-1366, and at the low end Clarkdale/Arrandale on LGA-1156. I'm not sure if there's enough room between them for Lynnfield, though I guess it does provide an easy upgrade option for inexpensive OEM systems which need to support Clarkdale.
brightstar - Sunday, May 31, 2009 - linkI'll wait and see how this pans out, but as of right now the I5 sounds like the new Celery proc to me
JS - Saturday, May 30, 2009 - link"...to protect the innocent"
I guess you really wanted to say "to protect my sources". I'm guessing they are not innocent at all, unless you actually stole the stuff from them. ;o)
mybook4 - Saturday, May 30, 2009 - linkThe article mentions that Lynnfield will have a new turbo mode that clocks much higher. I was thinking of reasons why intel might put this feature into the mainstream i5 rather than making the feature exclusive to the i7. Then I remembered that the PCIe controller was integrated into the core.
To overclock a multiplier locked i5, you would have to increase the base clock. Not sure, but I believe this would also overclock the PCIe controller (something which may not be as tolerant of overclocking).
This might explain why the new high end turbo mode would be included in the i5. You lose high overclocking potential (which would attract overclockers to i7), but in exchange, the i5 does decent overclocking for you.
pyn - Saturday, May 30, 2009 - linkis it possible that we will see turbo modes similar to lynnfield in gulftown? also, is intel going to release any 8 core / 16 thread nehalem processors targeted towards desktop systems or is the nehalem-ex likely to be the only 8 core nehalem we will see?
mmpalmeira - Saturday, May 30, 2009 - linkWhy did you use the Lynnfield in a 2.66Ghz configuration with HT on if there wont be models like that in the market?
Anand Lal Shimpi - Saturday, May 30, 2009 - linkI did that to show what sort of performance having HT enabled is responsible for. Intel isn't making a 2.13GHz HT enabled Lynnfield either, but I ran those tests because they're interesting to look at :)
Drazick - Saturday, May 30, 2009 - linkWill the P55 support USB 3, SATA 3, UEFI?
When will we see all those features in the chipsets, which for me, are much more important than the i5 by itself.
What about the new Chiopsets, are they SSD optimized?