Sun shimmers over Rainbow Falls

Sun has revealed details of its next generation CMT chip. The processor – dubbed ‘Rainbow Falls’ – will feature 16 cores per chip, along with extended, glueless node-to-node coherent interconnects.

According to Sanjay Patel of Sun, designers faced a number of challenges developing the Rainbow Falls chip, including on-chip connectivity, reducing interface counts, decreasing the area of larger components (L2 tags) and meeting the demands of four coherency units.

“Challenges exist in integrating more cores and more threads on chip, [while] coherent node-to-node interconnect adds another dimension,” said Patel. “Rainbow Falls addresses various technical challenges in a unique manner that can be leveraged to future generations.”

Patel explained that Rainbow Falls offered “massive buses” throughout the processor, with 16 cores interfacing to 16 L2 banks. In addition, the chip integrates 4 coherence units – with a set of 2 each interfacing independently to 3 high-speed links for remote node connectivity. As such, performance requirements had to be “carefully balanced” with the need to reduce area.

Finally, Patel discussed the demands of four coherency units – which support memor address requests and maintain coherence across SMP clusters.

He noted that area costs were in danger of becoming “prohibitive” unless dealt with “up front,” due to greater link bandwith requirements and support for “more outstanding” transactions.