Intel Core i7 In-Depth Performance Scaling Analysis

Overclocking/ by massman @ 2009-08-11

In this article we take a closer look at the overclocking aspects of the Core i7 platform. Core, uncore, QPI, memory, bclk... all have been analyzed with performance scaling tests to you help extract the most performance from your setup.

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QPI Link Frequency Performance Scaling

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Most people unfamiliar with the technical part of Intel's Core 2 and Core i7 platforms state that the BCLK is for i7 what the FSB is for Core 2. While that would indeed simplify things a lot, it's just not correct: the FSB, or Front Side Bus, frequency is the link between the Northbridge and the processor, which in i7 terms would be the QPI link. Basically, all data sent by the graphics card, sata, audio and so on travels through the IOH (Input/Output Hub) via the QPI link to the processor. In contrary to the C2D platform, the QPI link does not transfer any data from the memory banks since the memory controller has been re-assigned from the Northbridge to the CPU.

So to translate all this to scaling; in theory, by increasing the QPI link, we should only see a gain in 3D performance.

Madshrimps (c)
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Although the QPI link is the replacement of the FSB, which was one of the biggest factors in overclocking performance on the older generation of Intel processors, the link speed is now so high that even at the lowest setting available the performance is pretty much maxed out. We see a difference of less than 2% when increasing the frequency by 33%, which says enough.

We expect the QPI link to have a bigger effect once its bus speed will be used more, for instance in setups with two or more i7 processors. However, for desktop purposes, it's not necessary to even bother to overclock the QPI frequency. For the overclockers under us, especially those with a locked CPU, it's in any case best to set the QPI Link frequency multiplier at the lowest setting available.
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