The PERCS High-Performance Interconnect

The PERCS system was designed by IBM in response to a DARPA challenge that called for a high-productivity high-performance computing system. A major innovation in the PERCS design is the network that is built using Hub chips that are integrated into the compute nodes. Each Hub chip is about 580 mm² in size, has over 3700 signal I/Os, and is packaged in a module that also contains LGA-attached optical electronic devices. The Hub module implements five types of high-bandwidth interconnects with multiple links that are fully-connected with a high-performance internal crossbar switch. These links provide over 9 Tbits/second of raw bandwidth and are used to construct a two-level direct-connect topology spanning up to tens of thousands of POWER7 chips with high bisection bandwidth and low latency. The Blue Waters System, which is being constructed at NCSA, is an exemplar large-scale PERCS installation. Blue Waters is expected to deliver sustained Petascale performance over a wide range of applications. The Hub chip supports several high-performance computing protocols (e.g., MPI, RDMA, IP) and also provides a noncoherent system-wide global address space. Collective communication operations such as barriers, reductions, and multi-cast are supported directly in hardware. Multiple routing modes including deterministic as well as hardware-directed random routing are also supported. Finally, the Hub module is capable of operating in the presence of many types of hardware faults and gracefully degrades performance in the presence of lane failures.