Exploiting tightly-coupled cores

The individual processors of a chip-multiprocessor traditionally have rigid boundaries. Inter-core communication is only possible via memory and control over a core's resources is localised. Specialisation necessary to meet today's challenging energy targets is typically provided through the provision of a range of processor types and accelerators. An alternative approach is to permit specialisation by tailoring the way a large number of homogeneous cores are used. The approach here is to relax processor boundaries, create a richer mix of inter-core communication mechanisms and provide finer-grain control over, and access to, the resources of each core. We evaluate one such design, called Loki, that aims to support specialisation in software on a homogeneous many-core architecture. We focus on the design of a single 8-core tile, conceived as the building block for a larger many-core system. We explore the tile's ability to support a range of parallelisation opportunities and detail the control and communication mechanisms needed to exploit each core's resources in a flexible manner. Performance and a detailed breakdown of energy usage is provided for a range of benchmarks and configurations.