VIX: Virtual Input Crossbar for efficient switch allocation

Abstract

Separable allocators in on-chip routers perform switch allocation in two stages that often make uncoordinated decisions resulting in sub-optimal switch allocation. We propose Virtual Input Crossbars (VIX), where more than one virtual channel (VC) of an input port is connected to the crossbar. VIX improves switch allocation by allowing more than one input VC of an input port to transmit flits in the same cycle. Also, more input VCs can participate in the output arbitration, reducing the chances of uncoordinated decisions. VIX improves network throughput by more than 15% for the topologies studied without affecting the router critical path.