The Dark Knight: Intel's Core i7
by Anand Lal Shimpi & Gary Key on November 3, 2008 12:00 AM EST- Posted in
- CPUs
Turbo Mode: Gimmicky or Useful?
I refuse to make any further references to the Turbo buttons on PCs from the 80s and early 90s in this section :)
Intel's Core 2 processors have historically been quite overclockable, however most users don't overclock and thus they get no benefit from the added headroom in Intel's chips. Enthusiasts obviously benefit and get the performance of the best CPUs at much lower price points thanks to overclocking, but the rest of the world has all of this untapped power sitting under their heatsinks.
Varying clock speed according to system demands and temperature is nothing new, but it's predominantly done in the downward direction. At idle periods CPU clock speeds are dropped, when temperature limits are reached the same also happens, but why not boost clock speed when conditions are ideal?
This is exactly what Intel's Turbo mode does. Originally introduced on mobile Penryn, Turbo mode simply increases the operating frequency of the processor if conditions are cool enough for the CPU to run at the higher frequency. On mobile Penryn we only saw a frequency jump if one core was idle, but with Nehalem's Turbo mode all four cores can overclock themselves if temperatures are cool enough.
Each Nehalem can run its four cores at up to 133MHz higher than the stock frequency (e.g. 3.33GHz in the case of the 3.2GHz 965 model), or if only one core is active then it can run at up to 266MHz higher than stock (3.46GHz up from 3.2GHz).
I measured the impact of Nehalem's Turbo mode on the top bin Core i7-965, which runs at 3.2GHz by default but can ratchet up to 3.33GHz or 3.46GHz depending on whether the workload is single or multi-threaded:
| POV-Ray 3.7 | 3dsmax 9 SPECapc CPU Rendering Composite | x264 HD Benchmark (Pass 1 / Pass 2) | iTunes WAV to MP3 Convert | iTunes WAV to AAC Convert (Single Threaded) | |
| Intel Core i7-965 (3.2GHz, Turbo OFF) | 4017 PPS | 17.1 | 82.7 fps / 30.4 fps | 27.1 seconds | 34.1 seconds |
| Intel Core i7-965 (3.2GHz, Turbo ON) | 4202 PPS | 17.6 | 85.8 fps / 31.6 fps | 26.4 seconds | 32.8 seconds |
| Performance Advantage | 4.6% | 2.8% | 4.6% | 4.1% | 3.8% |
At best we should see a 4ish % increase in performance and the fact that POV-Ray shows us something greater than that tells us that Turbo mode works (and we're within the 1 - 2% margin of error of the test). Surprisingly enough, all of the multi-threaded tests had no problems using Turbo mode to their benefit giving us a 3 - 4% increase in performance thanks to the corresponding increase in clock speed. The AAC iTunes test is important as it is single-threaded, but despite the larger increase in clock speed performance didn't seem to improve any more.
Our Turbo testbed
Now these tests were conducted on an open-air testbench with an aftermarket cooler by Thermalright, we wondered what would happen if we used a retail Intel HSF and stuck the Core i7 in a system with a Radeon HD 4870 and a 1200W PSU. The CPU actually ran a lot warmer and Turbo Mode never engaged, pretty much as expected.
With Nehalem it may be worth investing in one of these oversized heatsinks, even if you're not overclocking, you'll get a couple of extra percent in the performance department if you can keep the cores cool.
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Kaleid - Monday, November 3, 2008 - link
http://www.guru3d.com/news/intel-core-i7-multigpu-...">http://www.guru3d.com/news/intel-core-i...and-cros...bill3 - Monday, November 3, 2008 - link
Umm, seems the guru3d gains are probably explained by them using a dual core core2dou versus quad core i7...Quad core's run multi-gpu quiet a bit better I believe.tynopik - Monday, November 3, 2008 - link
what about those multi-threading tests you used to run with 20 tabs open in firefox while running av scan while compressing some files while converting something else while etc etc?this might be more important for daily performance than the standard desktop benchmarks
D3SI - Monday, November 3, 2008 - link
So the low end i7s are OC'able?
what the hell is toms hardware talking about lol
conquerist - Monday, November 3, 2008 - link
Concerning x264, Nehalem-specific improvements are coming as soon as the developers are free from their NDA.See http://x264dev.multimedia.cx/?p=40">http://x264dev.multimedia.cx/?p=40.
Spectator - Monday, November 3, 2008 - link
can they do some CUDA optimizations?. im guessing that video hardware has more processors than quad core intel :PIf all this i7 is new news and does stuff xx faster with 4 core's. how does 100+ core video hardware compare?.
Yes im messing but giant Intel want $1k for best i7 cpu. when likes of nvid make bigger transistor count silicon using a lesser process and others manufacture rest of vid card for $400-500 ?
Where is the Value for money in that. Chukkle.
gramboh - Monday, November 3, 2008 - link
The x264 team has specifically said they will not be working on CUDA development as it is too time intensive to basically start over from scratch in a more complex development environment.npp - Monday, November 3, 2008 - link
CUDA Optimizations? I bet you don't understand completely what you're talking about. You can't just optimize a piece of software for CUDA, you MUST write it from scratch for CUDA. That's the reason why you don't see too much software for nVidia GPUs, even though the CUDA concept was introduced at least two years ago. You have the BadaBOOM stuff, but it's far for mature, and the reason is that writing a sensible application for CUDA isn't exactly an easy task. Take your time to look at how it works and you'll understand why.You can't compare the 100+ cores of your typical GPU with a quad core directly, they are fundamentaly different in nature, with your GPU "cores" being rather limited in functionality. GPGPU is a nice hype, but you simply can't offload everything on a GPU.
As a side note, top-notch hardware always carries price premium, and Intel has had this tradition with high-end CPUs for quite a while now. There are plenty of people who need absolutely the fastest harware around and won't hesitate paying it.
Spectator - Monday, November 3, 2008 - link
Some of us want more info.A) How does the integrated Thermal sensor work with -50+c temps.
B) Can you Circumvent the 130W max load sensor
C) what are all those connection points on the top of the processor for?.
lol. Where do i put the 2B pencil to. to join that sht up so i dont have to worry about multiply settings or temp sensors or wattage sensors.
Hey dont shoot the messenger. but those top side chip contacts seem very curious and obviously must serve a purpose :P
Spectator - Monday, November 3, 2008 - link
Wait NO. i have thought about it..The contacts on top side could be for programming the chips default settings.
You know it makes sence.Perhaps its adjustable sram style, rather than burning connections.
yes some technical peeps can look at that. but still I want the fame for suggesting it first. lmao.
Have fun. but that does seem logical to build in some scope for alteration. alot easier to manufacture 1 solid item then mod your stock to suit market when you feel its neccessary.
Spectator.