The Lynnfield Followup: Turbo Mode and Overclocking Investigated
by Anand Lal Shimpi on September 18, 2009 12:00 AM EST- Posted in
- CPUs
Lynnfield vs. Bloomfield: Overclocked and Without Turbo
The second request was how Lynnfield and Bloomfield stacked up with turbo disabled but when overclocked. At higher frequencies the demands on the memory subsystem go up so it's more than a valid concern.
I took both systems and overclocked them to 3.8GHz, a level that wasn't too difficult to achieve (more on this later):
The average performance difference doesn't appear to change even as we scale up clock speed. Lynnfield actually does better here thanks to better than expected scores in the game tests (the on-die PCIe controller to blame?), but also falls behind in some other tests (e.g. x264). Overall the performance difference seems to hold even when overclocked; the performance you give up when going to Lynnfield at stock speeds with turbo disabled doesn't get any worse at overclocked speeds.
It's also worth noting that there are applications that we haven't tested that could demand even more of the memory subsystem, but on average, for most users I'd say that the third memory channel isn't worth the price difference.
Hitting 3.8GHz: The Good, The Bad and The Ugly
I picked 3.8GHz for the comparison on the previous page and I just wanted to share what I had to do to reach that frequency.
Bloomfield was by far the easiest to get up to 3.8GHz. I just increased the BCLK and the system POSTed at 3.8GHz. After going through several benchmarks I found that I needed to add a tiny bit of voltage (~40mV) to make it completely stable, but I really didn't have to do anything above and beyond that.
Lynnfield was a bit more difficult. After increasing the BCLK there was a lot more guess and test of voltage levels before I could get the system completely stable. As I mentioned in our Lynnfield launch article, thanks to the on-die PCIe controller any serious overclock will require a bit of voltage. I ended up running the chip at around 1.265V for full stability.
It was far easier to overclock Lynnfield if I just used voltages above 1.30V, but then I ran into another problem: heat. The chip wouldn't hit 3.8GHz regularly at such high voltages, although Gary's testing indicates that a bigger heatsink/fan could fix that. With some work you can definitely overclock Lynnfield using the retail heatsink/fan, it's just not nearly as easy as Bloomfield.
And finally we get to the Phenom II X4 965 BE. With Vista 32-bit installed, the Phenom II system had no problem running at 3.8GHz - however all of our application tests run under a 64-bit OS and this is the Phenom II's achilles' heel. Getting the system stable at 3.8GHz in a 64-bit OS was the most difficult out of the three overclocks I performed for this article. The chip required an uncomfortable amount of voltage and ultimately I couldn't get my sample 100% stable at 3.8GHz in 64-bit Vista (although 32-bit OSes weren't an issue).
If you're curious, the performance gap between AMD and Intel does widen considerably at these higher frequencies:
| Processor | Adobe Photoshop CS4 | DivX | x264 - 1st Pass | x264- 2nd Pass | WME |
| AMD Phenom II @ 3.8GHz | 19.5 seconds | 39.1 seconds | 85.0 fps | 22.2 fps | 26 seconds |
| Intel Bloomfield @ 3.8GHz | 13.3 seconds | 28.8 seconds | 100.0 fps | 36.3 fps | 21 seconds |
| Intel Lynnfield @ 3.8GHz | 13.6 seconds | 29.0 seconds | 95.7 fps | 33.9 fps | 24 seconds |
Power Consumption While Overclocked
Guru3D pointed out an important observation in their Lynnfield review: power consumption goes up considerably when you overclock. It's not just the overclock, but it's the process of increasing core voltage that makes power consumption skyrocket. This is partly why I stress stock-voltage overclocking so much. Let me give you an example:
| Processor | Stock Power Consumption | Power Consumption While Overclocked to 3.8GHz @ 1.3V |
| Intel Core i7 875 | 181W | 215W |
That's a pretty hefty gain in power consumption, over 18% but we get a 29.% increase in clock frequency. Remember my troubles getting the Phenom II X4 965 BE to work in 64-bit Windows? I ran some numbers to show exactly what a lot of extra voltage will do to power consumption:
| Processor | Stock Voltage @ 3.4GHz | Stock Voltage @ 3.8GHz | +0.2Vcore, +0.1V NB @ 3.8GHz |
| AMD Phenom II X4 965 BE | 223W | 239W | 300W |
Increasing the clock speed by 400MHz only drives up power consumption by 7%, boosting voltage on top of that results in an additional 25% power gain. When overclocking you always want to increase as much as possible while adding as little voltage as possible to maintain the most power efficient system.
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coconutboy - Saturday, September 19, 2009 - link
Good article. There are a number of great hardware sites out there, but I do appreciate that you fellas at anandtech not only get out the info fast, but also in depth. I was especially interested in the stock voltage (or near to it) overclocking comparisons with i7 920 vs i7 860 both with and without turbo enabled. I was pretty sure I wanted an i7 920 versus the 860, but this article along w/ some early forum board results pretty much seals it.I understand that anandtech has to go by the prices of reliable online retailers or else chains like Best Buy etc, but for overclockers with a microcenter nearby I think i7 920 is a better value than 860. Lynnfields turbo modes are of dubious value for OCers, even conservative ones like me. I plan on running a low OC of ~3.4GHz which likely makes 860's turbo modes much more attractive to me versus more aggressive OCers, but still find the total system cost/performance of even a moderately overclocked 860 to be negligible vs 920 because-
1) I can buy a 920 for $200 vs $230 for the 860.
2) There are a number of excellent 1366 mobos in the $170-200 range. Most 1156 mobos which compare featurewise to those sub-$200 x58 mobos are at least $150 with many costing the same price as X58. Combined w/ a cheaper CPU from microcenter, Lynnfield offers me nothing pricewise.
3) x58 is a safer and easier OC since it doesn't fiddle w/ the PCIe. This is of particular interest for those of us who might be diving in early to the upcoming (and probably $$) ATI/Nvidia GPUs. x58 = Less challenge for the tweakers but a safer bet for the set-it-and-forget-it crowd who don't want issues later on.
4) The cost per GB of low-latency DDR3 is a almost identical for 3x2GB and 2x2GB kits. I easily chew up 4GB of RAM on my currrent system, so 6 or even 12GB is much more attractive.
If you have the ability to buy your cpu from a nearby microcenter or someplace with similar prices the main attraction for buying an i7 860 seems to be-
1) running stock speeds/low OCs
2) buying a low-cost $100-120 mobo that skimps on a few features.
3) you want the coolest running i7 CPU possible
4) new and shiny ooooh.
I'll buy 920 for me, and probably pick up 860 with one of those $100-120 mobos for the woman. Now please hurry up and pass NDA, I'm curious about the new ATI GPUs.
ginbong - Monday, September 21, 2009 - link
You forgot about the idle and load power consumption.Lynnfield has really low power consumption. I'm one of the slight OC with stock voltage persons but I think if you will only be running a single high end GPU or a dual GPU on one PCB then the Lynnfield is the way to go for stock clocks relying on the aggressive turbo to keep the power consumption down. (I normally take off my overclocks when I don't play for a few months.)
Lynnfield would have been great if it wasn't for the linked PCI-e on die controller.
I'm undecided yet because I'm not sure about how to handle that while overclocking so I'll be waiting for more articles related to that issue. *wink* *wink* AnandTech staff
JamesA - Saturday, September 19, 2009 - link
From looking at the benchmarks, it seems that in Gaming the Core2Duo E8600 and the Core2Quad Q9650 perform very well. It seems to be mostly in the Photoshop / 3D rendering tests that they move way down the charts.So if you are mostly doing Gaming and already have a good system that could handle the E8600/Q9650 it would seem there was not a specific value right yet in spending all the money to upgrade to an i5/i7 system.
Zoomer - Saturday, September 19, 2009 - link
From the benchmark results, would I be right to extrapolate that there is no real reason to get a Lynnfield if one solely focused on gaming performance?The 2.66Ghz C2Q is clock matched with the i5, but remains on par most of the time, despite the i5 dynamically overclocking. I surmise that a C2Q at a frequency = max i5 turbo freq would beat the i5. Furthermore, since the i5 is not that great of an overclocker, max C2Q freq > i5 freq, but $C2Q << $i5 due to the newer platform & need for DDR3. P55 mobos, cooling solutions, ram all cost more.
Hopefully someone can run some benches and do a comparison to squash such speculation. ;)
nevbie - Saturday, September 19, 2009 - link
Penryn and the Radeons like each other. Though these results are with 4 cores only..Patrick Wolf - Saturday, September 19, 2009 - link
So do those gaming results mean your going to post results of future GPU benchmarks on both Intel and AMD hardware?TA152H - Saturday, September 19, 2009 - link
I read this, and I'm really confused.The on-die PCIe should make the Lynnfield slower, right? The reason the benchmarks close up a little on games at higher clock speeds is the bottleneck probably moves more towards the GPU.
If you notice on your next page, you see that at higher resolutions the i7 920 starts creeping up. You could say this is the reverse, but in some situations it actually passes the Lynnfield. This is because of the inferior PCIe implementation on the Lynnfield, probably. In this event, you're probably have more collisions, because of the higher resolutions, you're using main memory for video. Consequently, the weaker on-die implementation starts to falter, while the x58 doesn't have the memory contention issue.
That's my guess anyway. It's going to be as hard to get people to understand this as it was for them to understand the additional stages for the K8 were for IPC, not clock speed, but ...
On-die PCIe isn't going to boost performance, it should hurt it. Unless Intel did something weird and gave the Lynnfield a separate memory bus for PCIe, all the memory requests from the video cards now have to go through the processor. If the processor and video card want to access memory at the same time, you lose performance. The x58 doesn't have to use the wider memory bus of the Bloomfield, so this problem doesn't exist.
This would explain some of your benchmark results. You'd see it more if you actually used proper memory. Not that you'd want to.
I'm not sure of this, but so far benchmarks seem to imply it, and I've seen nothing to disprove it. Have you heard something different from Intel? I really don't think they would have a separate memory bus for PCIe, when you think of how infrequently, relatively speaking, it would be used. So, it seems very likely there is a potential contention issue, and on-die PCIe would lower performance, not increase it.
lopri - Saturday, September 19, 2009 - link
Your explanation seems plausible at first but it fails to account for:1) That the symptom more or less disappears with AMD GPU.
2) That the Bloomfield suffers the same thing as the Lynnfield.
3) That it is not Intel CPU under-performing but rather AMD CPU (or platform) better performing when coupled with NV GPU. I deduce this partially from C2Q-P45's showing under GPU-limited scenarios.
These are subtle yet important distinctions, IMO.
goinginstyle - Saturday, September 19, 2009 - link
TA152H...Where is your article about P55 being "brain damaged" at your review site? Where are all of your benchmarks proving that the 920 "wipes the floor" with the 860? Where are all your benchmarks proving that the 920 is faster with higher speed memory? So far none of the benchmarks here or elsewhere even show what you claim. How is that next copy and paste article coming along for you by the way?
TA152H - Saturday, September 19, 2009 - link
You saw them here, you twit.Although, I'm not crazy about him running the uncore on the Bloomfield faster. The results are skewed. They would be lower were it not for that.
Still, let's say 3%. When you see 3% just from changing the CPU, considering the other parts, that's a big difference. With caches being so effective, getting 3% difference from the same architecture, on average, is pretty big.
On some, it's much bigger.
Did you learn something, moron?