A computer-implemented method of performing an operation on an array of values at a processing unit so as to perform a phase of the operation. For each of one or more one-dimensional sequences of values of the array of values a respective section of values of the one-dimensional sequence of values is assigned to each of a plurality of threads, and a first thread of the plurality of threads determines at least one contribution, from the section of values assigned to the first thread, to the phase of the operation that is to be completed by a second thread of the plurality of threads for a neighbouring section of values of the one-dimensional sequence of values. The at least one contribution is written to a memory, and a second thread of the plurality of threads reads the at least one contribution from the memory. and completes the phase of the operation for the neighbouring section of values assigned to the second thread in dependence on the at least one contribution read from the memory in order to generate a section of processed values.