Although Intel has never revealed there is some connection between the BCLK/QPI and iGPU frequency/performance, our tests have shown there is definitely one.
The integrated GPU of Clarkdale is still based on GMA (Graphics Media Accelerator) architecture, and thanks to the more advanced 45nm manufacturing process and addition of new technologies to boost performance, it can be regarded as the enhanced version of Intel X4500 HD graphics core which powers Intel G45 motherboard. We’re using this graphics unit with iGPU clock of 733MHz for the test.
Note: there is no software capable of monitoring the Clarkdale real-time iGPU clock – the CPU-Z utility can just read the original iGPU clock.
We found something interesting: the BCLK has an obvious impact on iGPU clock.
Our test indicates that under the same iGPU clock, the multi-texturing performance improves significantly with the increase of BCLK. The change of iGPU frequency was the same as the BCLK change – when the BCLK raised from 133MHz to 166MHz, the iGPU clock also improved accordingly by 166/133=125%. With GPU clock of 733MHz, it was actually running at 915MHz when BCLK was 166MHz.
This has explained why iGPU worked perfectly well at 1133MHz when BCLK was 133MHz, while the iGPU clock couldn’t even reach 833MHz when BCLK increased to 200MHz, as the iGPU clock had achieved up to 1250MHz, and the system became unbootable.
We’ve concluded a formula which will give you a rough idea of the relationship.
Real-time iGPU clock = Preset iGPU clock * BCLK / 133