X-bit labs

Intel Core 2 Extreme QX6700 and Core 2 Quad Q6600 Processors: Quad-Core CPUs Gone Real! (page 10)

Category: CPU

by Ilya Gavrichenkov

[ 11/01/2006 | 10:31 PM ]

Multi-Tasking

In this section we performed a few tests aimed at revealing the systems performance where there are a few applications running simultaneously. We launched several resource-hungry tasks in different applications and measured the time it took the test platforms to complete them.

Here we were processing an image in Adobe Photoshop and at the same time compressing a folder with files using WinRAR utility. I have to admit that we were not at all surprised with the results. Multi-core processors coped with multitasking easily, leaving dual-core Conroe more than 30% behind.

Then we were editing video in Adobe Premiere Pro and encoding an MP3 file using Apple iTunes. Looks like the computational workload was higher than in the previous case. At least Kentsfield proved 93% faster than Conroe working at the same clock frequency.

The third test is probably the most sophisticated. Our test platforms were busy working on three tasks at a time: image editing in Adobe Photoshop, final rendering in 3ds max and video encoding into MPEG4 format. And once again quad-core processors proved to be the best choice having outperformed dual-core Conroe pretty noticeably. So, we have every right to say that multi-core processors will come in very handy in systems running multiple tasks at the same time.

Besides the performance of the dual-core and quad-core platforms running several parallel tasks, we also decided to investigate the influence of background processes on the performance in certain resource-hungry applications. We measured the fps rate in Quake 4 game with several copies of WinRAR utility running in the background.

At first glance the results appeared pretty discouraging. We would expect a CPU with more cores to be faster, no matter how many applications are running in the background. But the real state of things turned out different. Although Kentsfield based platform runs faster with a few applications in the background, we cannot observe the same tendency for situations with higher number of background apps. In case of 6+ applications in the background, the performance of the “primary” game drops faster in a quad-core system.

Let’s try to get to the roots of things here. It is important to understand that the performance of the game drops not because the background archiving tools eat up all the processor resources. Windows OS task manager distributes all processes very nicely, so that all background tasks get sent to the idling cores. However, all background tasks do not require only CPU resources. They also need access to other platform subsystems, such as front side bus and memory bus. This seems to be the problem for Kentsfield. Since this processor consists of two different semiconductor dies, they exchange data via front side bus and system memory. And WinRAR is a multi-threaded application that involves a few cores at the same time. So, if you have this utility running in the background it eats up some of the memory bus and front side bus bandwidth in order to exchange data between different application threads. Therefore, if you have a few copies of this program running on a Kentsfield based platform, the bus bandwidth gets used up much sooner than in a Conroe based platform where the data is exchanged via the shared L2 cache.

However, this is no tragedy at all. We used this relatively artificial test to show the potential bottleneck of Kentsfield architecture. It will be really hard to stumble upon the same situation in real life, because most background processes are not that resource-consuming. And if any “heavy-duty” tasks are running in the background, there are not too many of them, as a rule.