Adaptive Synchronisation: Optimising the Locality of Collective Communications in an Adaptive Setting

Gardens is a system which supports adaptive parallel computation across networks of workstations. This is achieved by over decomposing a program into more tasks than there are processors. Tasks are migrated to realise adaptation to changing workstation loads e.g. the coming and going of interactive users. Gardens supports a virtual shared object space. Object references are location transparent in that they may reference an object belonging to a task local to the same workstation or remote, on another workstation. This form of location transparency simpliies programming but can result in ineecient communications for collective communication operations. This paper presents an approach where location information is used as a heuristic to optimise communication. In keeping with the Gardens philosophy of supporting the programming of parallelism and communication abstractions, this is not built-in behaviour but can be programmed based on a few simple primitives; it is also safe. This paper presents the Gardens approach to communication and its optimisation and the implementation of an adaptive synchronisation abstraction .