Guaranteed Services of the NoC of a Manycore Processor

The Kalray MPPA®-256 processor (Multi-Purpose Processing Array) integrates 256 processing engine (PE) cores and 32 resource management (RM) cores on a single 28nm CMOS chip. These cores are distributed across 16 compute clusters and 4 I/O subsystems. On-chip communications and synchronization are supported by an explicitly routed dual data & control network-on-chip (NoC), with one node per compute cluster and 4 nodes per I/O subsystem, for a total of 32 nodes. The data NoC is dedicated to streaming data transfers and may operate with guaranteed services, thanks to non-blocking routers and flow regulation at the source node. Its architecture has been designed so that (σ, ρ) network calculus applies with minimal approximations. Given a set of flows across this data NoC with predetermined routes, we formulate the problem of guaranteeing fair allocation of bandwidth across flows and we present bounds on the maximum transfer latency. By considering the architecture of the data NoC and by introducing conservative approximations, we show how this formulation can be transformed into a linear program. Solving this linear program is efficient and the quality of its solutions appears comparable to those of the original formulation, based on problem instances obtained from the cyclostatic dataflow compilation toolchain of the Kalray MPPA®-256 processor.