To help tolerate the latency of accessing remote data in a shared-memory multiprocessor, we explore a novel approach to switch-on-miss multithreading that is software-controlled rather than hardware-controlled. Our technique uses informing memory operations to trigger the thread switches with sufficiently low overhead that we observe speedups of 10% or more for four out of seven applications, with one application speeding up by 14%. By selectively applying register partitioning to reduce thread switching overhead, we can achieve further gains: e.g., an overall speedup of 23% for FFT. Although this software-controlled approach does not match the performance of hardwarecontrolled schemes on multithreaded workloads, it requires substantially less hardware support than previous schemes and is not likely to degrade single-thread performance. As remote memory accesses continue to become more expensive relative to software overheads, we expect software-controlled multithreading to become increasingly attractive in the future.