Analysis: Dual Core technology

Posted on 27 May 2005 at 11:02

system control. This means that for desktop applications, the power consumption should on average be much lower than TDP. The heatsink supplied with our EE processor was the same design supplied with current single-core parts and encouragingly didn't get noticeably hot in operation.

How does dual core relate to multithreading?
Up until now, mainstream CPUs have been serial-processing devices. Increases in performance have come through, upping the speed at which the processor does a single operation, and it does these one at a time.

Dual core marks a sea change in that approach; as of this very month, mainstream computing has gone parallel. Rather than completing a given operation faster to enable it to get through more operations one after the other, parallel processors do two things at once.

In fact, at the very low level of CPU architecture, parallelism has existed for years, but this involves breaking code down piecemeal at runtime for faster execution while it's going through the processor. This approach can only go so far - the CPU isn't intelligent and can't make parallel optimisations that look ahead further than the next few blocks of instructions.

With multithreaded applications executed on dual-core processors, everything is different. Instead of the software handing the CPU one task at a time and hoping it can make do, the onus is on the human programmer. The CPU expects to be handed two clearly defined tasks at a time; if it's
not, then half of the processing power on offer is wasted as one of the
two cores sits idle.

And that's the big change that makes dual- and multi-core processing a double-edged sword. It can deliver huge performance gains but only if two conditions are satisfied: first, that the problem in hand is suitable for splitting in two at the conceptual level and, second, that the programmer has sufficient skill to handle that task, writing software to take advantage of the two processors on offer. Writing multithreaded applications is a far more difficult task than would first appear, primarily because humans naturally think in a consecutive way, doing one thing after another. This major hurdle is the reason Intel is spending millions of dollars to re-educate developers, placing literally thousands of its own engineers in the development workshops of major software houses like Oracle and SAP in order to shepherd its developers and ease the intellectual burden of developing multithreaded applications.

Results
The perfect demonstration of both the benefits and disadvantages of multithreading and dual core comes from a test render using discreet's 3ds max 7. Remember that rendering is purely a CPU and memory-bandwidth test, on which 3D graphics performance has no bearing. Now look at the results compared to Intel's fastest single-core processor, the 3.73GHz Pentium 4 EE, directly swapped into the test setup. You can see that with 3ds max's multithreaded rendering enabled, the dual-core processor obliterates the single core with performance nearly twice as fast. But turn off the multithreading and the render is performed in just the one core of the dual-core part. Its time is more than doubled and the single-core 3.73GHz CPU beats it. If the developers of 3ds max hadn't bothered to make their application properly multithreaded, even a four- or eight-core processor would be beaten by the faster-clocked single core.
Note that the single-core part gets some benefit from Hyper-Threading when 3ds max's multithreading is enabled, but nowhere near the boost that a true second core gives you.