NoCMsg

As today's manycore processors already feature over 64 cores and as tomorrow's are slated to contain 1000s, it is important to design operating system techniques that can efficiently cope with this scale of resource coordination. The current state-of-the-art in manycore processor architectures has evolved from traditional bus-based architectures over rings to mesh-based Network-on-Chip (NoC) interconnects. This implies an increasing potential for scalable message passing. However, contemporary operating systems heavily rely on single system images with shared memory constructs that may not scale well to large core counts. To address these challenges, we devise a distributed message passing only system comprised of so-called "pico-kernels" per core. They are controlled by dedicated "micro-kernels" topologically centered within a set of cores that cooperatively comprise the overall operating system in a peer-to-peer fashion.Such a system promotes rethinking and redesigning of various operating system services focusing on scalability as the primary design constraint. We consider the challenges of distributed allocation of jobs, each comprised of a set of tasks to be mapped to disjoint cores. A naive solution performing fragmented allocations may quickly escalate to deadlocks, where jobs hold and wait for cores in circular dependencies. To tackle these challenges, we propose a deadlock free distributed job allocation protocol. We have devised two policies for avoiding deadlocks, namely active cancellation and sequencer-based atomic broadcast. The protocol and the two policies have been implemented and evaluated on a Tilera TilePro64 processor with 64 cores on a single socket. Results show that for sparse job allocations active cancellation provides less job allocation overhead while for denser job allocations the sequencer-based atomic broadcast provides less overhead.

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