As promised, this short article will be devoted to the analysis of probably one of the most interesting technologies used in Intel Core i7 processors -- Hyper-Threading. We were interested in a simple issue: when there are four physical cores, each split into two logical cores by HT, totalling in 8 processors per system, even an operating system may get lost in its cores. Especially as the issue of interaction between Windows Vista x64 Ultimate and eight processors hasn't been studied well enough. It's reasonable to assume that Microsoft Vista hasn't been prepared for that stuff. That's why the previous article provided some food for thought, but it didn't satisfy our curiosity about HT completely: we had to cover too much -- physical cores, logical cores, technologies.

How can we create the most favorable conditions for Hyper-Threading? We decided to use the simplest method. Indeed, two cores are not eight, most programs handle two cores very well. So when Hyper-Threading emulates only two cores instead of eight, pros and cons of this technology should reveal themselves in the most pronounced way. So this time we shall not try to reproduce a realistic situation, we'll do on the contrary: we'll provide perfect conditions for Hyper-Threading to reveal its true worth. That's what we've done: first of all we disabled in BIOS all cores but one in the Core i7, we disabled Turbo Boost (to fix the operating frequency). After that we measured system performance without Hyper-Threading (in this case the operating system detected our processor as a single-core model) and with Hyper-Threading enabled (in this case the operating system detected two cores, but it worked with one core anyway). Then we enabled two cores in BIOS, disabled Turbo Boost and Hyper-Threading, and reran our tests. Thus, we got an opportunity to analyze how useful Hyper-Threading is in a practically perfect situation from two point of view: comparison with the honest single-core system (without HT) will show us how useful Hyper-Threading is. And comparison of a HT system with the honest dual-core system will demonstrate how worse virtual multiple cores are versus real multiple cores.

Besides, in this case we test not only Hyper-Threading, but also software to some degree: is it ready to use virtual cores? Can it utilize their features? At at least not slow down?

Testing

Testbed configuration

• CPU: Intel Core i7 950
• Cooler: ASUS Triton 81
• Motherboard: ASUS P6T SE (Intel X58)
• Memory: 3 x 2GB Corsair DDR3-1800 in DDR3-1600 mode
• Graphics card: Palit GeForce GTX 275
• PSU: Cooler Master Real Power M1000

We traditionally publish a link to a Microsoft Excel spreadsheet for curious readers, which contains all test results in the most detailed form. Besides, it includes an additional tab "Compare" to facilitate their analysis. Just like the tables in the article, it compares the situations percentagewise. Tables are colored in the traditional way: bright blue background marks outstanding positive results (in this case we marked performance gains above 10%), red background signals problems: performance drops where we should have performance gains (or at least no changes). Performance gain percent is always calculated relative to the leftmost system (single core, no HT).

We'll publish only short comments to the diagrams, because in the previous article we wrote much about the effect of Hyper-Threading on performance. So we are going to pay attention only to interesting results that differ from the previous article.

3D visualization

* The up arrow (↑) marks tests, where the highest results are the best, the down arrow (↓) marks tests, where the best results are the lowest.

Maya and Lightwave were champions in the previous article (but in the other order), and they shine here as well. SolidWorks responded to HT by slowing down on a quad-core system. But in this case it's more disposed to this technology. By the way, we'll see similar situations many times.

3D rendering

The average performance gain from HT on a quad-core system in this group amounted to 21%. In this case (single core) it's 25%. It's formally bigger, but frankly speaking we expected higher contrast.

Scientific and engineering analysis

There is a comic situation in this group of scientific and engineering applications: three programs out of seven (almost half) rejected Hyper-Threading in our previous article -- they dropped performance when HT was enabled. We can see nothing of the sort here, on the contrary: performance drop in MATLAB turned into a noticeable gain.

Raster graphics

It's a similar situation again: most packages responded negatively to HT last time (4 out of 5). This situation on a single-core system is cardinally different: three programs out of five demonstrate performance gains.

Data compression

Performance gains are much higher here: in general, 16% versus 3% in the previous article. However, it's easy to explain: archivers can use two cores effectively, so we could expect advantage of the HT system over an honest single-core computer.

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