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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Spectator - Monday, November 3, 2008 - link
that sht is totally logical.And Im proper impressed. I would do that.
you can re-process your entire stock at whim to satisfy the current market. that sht deserves some praise, even more so when die shrinks happen. Its an apparently seemless transition. Unless world works it out and learns how to mod existing chips?
Chukkle. but hey im drunk; and I dont care. I just thought that would be a logical step. Im still waiting for cheap SSD's :P
Spectator.
tential - Monday, November 3, 2008 - link
We already knew nehalem wasn't going to be that much of a game changer. The blog posts you guys had up weeks ago said that because of the cache sizes and stuff not to expect huge gains in performance of games if any. However because of hyperthreading I think there also needs to be some tests to see how multi tasking goes. No doubt those gains will be huge. Virus scanning while playing games and other things should have extremely nice benefits you would think. Those tests would be most interesting although when I buy my PC nehalem will be mainstream.npp - Monday, November 3, 2008 - link
I'm very curious to see some scientific results from the new CPUs, MATLAB and Mathematica benchmarks, and maybe some more. It's interesting to see if Core i7 can deliver something on these fronts, too.pervisanathema - Monday, November 3, 2008 - link
I was afraid Nehalem was going to be a game changer. My wallet is grateful that its overall performance gains do not even come close to justifying dumping my entire platform. My x3350 @ 3.6GHz will be just fine for quite some time yet. :)Additionally, its relatively high price means that AMD can still be competitive in the budget to low mid range market which is good for my wallet as well. Intel needs competition.
iwodo - Monday, November 3, 2008 - link
Since there are virtually no performance lost when using Dual Channel. Hopefully we will see some high performance DDR3 with low Latency next year?And which means apart from having half the core, Desktop version doesn't look so bad.
And since you state the Socket 1366 will be able to sit a Eight Core inside, i expect the 11xx socket will be able to suit a Quad Core as well?
So why we dont just have 13xx Socket to fit it all? Is the cost really that high?
QChronoD - Monday, November 3, 2008 - link
How long are they going to utilize this new socket??$284 for the i7-920 isn't bad, but will it be worth the extra to buy a top end board that will appreciate a CPU upgrade 1-2 years later? Or is this going to be useless once Intel Ticks in '10?
Strid - Monday, November 3, 2008 - link
Great article. I enjoyed reading it. One thing I stumbled upon though."The PS/2 keyboard port is a nod to the overclocking crowd as is the clear CMOS switch."
What makes a PS/2 port good for overclockers? I see the use for the clear CMOS switch, but ...
3DoubleD - Monday, November 3, 2008 - link
In my experience USB keyboards do not consistently allow input during the POST screen. If you are overclocking and want to enter the BIOS or cancel an overclock you need a keyboard that works immediately once the POST screen appears. I've been caught with only a USB keyboard and I got stuck with a bad overclock and had to reset the CMOS to gain control back because I couldn't cancel the overclock.Clauzii - Monday, November 3, 2008 - link
I thought the "USB Legacy support" mode was for exactly that? So legacy mode is for when the PC are booted in DOS, but not during pre?sprockkets - Monday, November 3, 2008 - link
No, USB legacy support is for support during boot up and for the time you need input before an OS takes control of the system. However, as already mentioned, sometimes USB keyboards just don't work in a BIOS at startup for one reason or another, and in my opinion, this means they should NEVER get rid of the old PS/2 port.I ran into this problem with a Shuttle XPC with the G33 chipset, which had no ps/2 ports on it. There was a 50/50 chance it would not work.