Latency is one of the biggest performance killers for supercomputers. But high bandwidth also is a problem. PathScale's HTX-based InfiniPath adapter addresses both challenges, melding the bandwidth of a 4X InfiniBand link to a low-latency HyperTransport link (see the figure). The resulting latency through a single-level InfiniBand switch is only 1.5 ms.
HTX is the new adapter card form factor from the Hyper-Transport Consortium. It permits direct, off-board connections from processors like AMD's Opteron. The standard is being implemented on motherboards like IWill's DK8S2-HTX dual-processor EATX board, which has a single HTX slot that's ideal for the InfiniPath adapter. A single adapter can handle up to eight HyperTransport-based processors.
Pathscale gets great performance and low latency by playing fast and loose with the InfiniBand implementation. In fact, the subset it implements enables InfiniBand management of the adapter. But the adapters themselves only work with each other, though the InfiniBand switch fabric can carry PathScale and standard Infini-Band traffic at the same time. The lack of overhead lets the Infini-Path adapter cut latency significantly while boosting performance. The link has 1.8 Gbits/s of bi-directional bandwidth.
The InfiniPath HTX adapter will cost under $1000, making it one of the least expensive supercomputing interconnects that meets or exceeds the performance of other alternatives.
InfiniBand Trade Association