One might think that it would be easiest to use MPI to allocate one instance of the MPI application to a single CPU core on each cluster node, and this would be true. It would, however, not be the fastest solution.
Although for communication between processes across a network MPI is likely the best choice in this context, within a single system (single or multi-CPU system) using multithreading makes a lot of sense.
The main reason for this is simply that communication between threads is significantly faster than inter-process communication, especially when using a generalized communication layer such as MPI.
One could write an application that uses MPI to communicate across the cluster's network, whereby one allocates one instance of the application to each MPI node. The application itself would detect the number of CPU cores on that system, and create one thread for each core. Hybrid MPI, as it's often called, is therefore commonly used, for the advantages it provides:
- Faster...