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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npp - Tuesday, November 4, 2008 - link
Well, the funny thing is THG got it all messed up, again - they posted a large "CRIPPLED OVERCKLOCKING" article yesterday, and today I saw a kind of apology from them - they seem to have overlooked a simple BIOS switch that prevents the load through the CPU from rising above 100A. Having a month to prepare the launch article, they didn't even bother to tweak the BIOS a bit. That's why I'm not taking their articles seriously, not because they are biased towards Intel ot AMD - they are simply not up to the standars (especially those here @anandtech).gvaley - Tuesday, November 4, 2008 - link
Now give us those 64-bit benchmarks. We already knew that Core i7 will be faster than Core 2, we even knew how much faster.Now, it was expected that 64-bit performance will be better on Core i7 that on Core 2. Is that true? Draw a parallel between the following:
Performance jump from 32- to 64-bit on Core 2
vs.
Performance jump from 32- to 64-bit on Core i7
vs.
Performance jump from 32- to 64-bit on Phenom
badboy4dee - Tuesday, November 4, 2008 - link
and what's those numbers on the charts there? Are they frames per second? high is better then if thats what they are. Charts need more detail or explanation to them dude!TSM
MarchTheMonth - Tuesday, November 4, 2008 - link
I don't believe I saw this anywhere else, but the spots for the cooler on the Mobo, they the same as like the LGA 775, i.e. can we use (non-Intel) coolers that exist now for the new socket?marc1000 - Tuesday, November 4, 2008 - link
no, the new socket is different. the holes are 80mm far from each other, on socket 775 it was 72mm away.Agitated - Tuesday, November 4, 2008 - link
Any info on whether these parts provide an improvement on virtualized workloads or maybe what the various vm companies have planned for optimizing their current software for nehalem?yyrkoon - Tuesday, November 4, 2008 - link
Either I am not reading things correctly, or the 130W TDP does not look promising for the end user such as myself that requires/wants a low powered high performance CPU.The future in my book is using less power, not more, and Intel does not right now seem to be going in this direction. To top things off, the performance increase does not seem to be enough to justify this power increase.
Being completely off grid(100% solar / wind power), there seem to be very few options . . . I would like to see this change. Right now as it stands, sticking with the older architecture seems to make more sense.
3DoubleD - Tuesday, November 4, 2008 - link
130W TDP isn't much worse for previous generations of quad core processors which were ~100W TDP. Also, TDP isn't a measure of power usage, but of the required thermal dissipation of a system to maintain an operating temperature below an set value (eg. Tjmax). So if Tjmax is lower for i7 processors than it is for past quad cores, it may use the same amount of power, but have a higher TDP requirement. The article indicates that power draw has increased, but usually with a large increase in performance. Page 9 of the article has determined that this chip has a greater performance/watt than its predecessors by a significant margin.If you are looking for something that is extremely low power, you shouldn't be looking at a quad core processor. Go buy a laptop (or an EeePC-type laptop with an Atom processor). Intel has kept true to its promise of 2% performance increase for every 1% power increase (eg. a higher performance per watt value).
Also, you would probably save more power overall if you just hibernate your computer when you aren't using it.
Comdrpopnfresh - Monday, November 3, 2008 - link
Do differing cores have access to another's L2? Is it directly, through QPI, or through L3?Also, is the L2 inclusive in the L3; does the L3 contain the L2 data?
xipo - Monday, November 3, 2008 - link
I know games are not the strong area of nehalem, but there are 2 games i'd like to see tested. Unreal T. 3 and Half Life 2 E2.. just to know how does nehalem handles those 2 engines ;D