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## Achieving High Performance on a Network of Workstations

If a network meets the following guidelines, ScaLAPACK will perform well on it (see section 5.1.1). If a network of workstations does not meet one or more of these guidelines, read the rest of this chapter for more information.

- The bandwidth per node, if measured in Megabytes per second per node, should be no less than one tenth of the peak floating-point rate as measured in megaflops/second/node.
- The underlying network must allow simultaneous messages, that is, not standard ethernet and not FDDI .
- Message latency should be no more than 500 microseconds.
- All processors should be similar in architecture and performance. ScaLAPACK will be limited by the slowest processor. Data format conversion significantly reduces communication performance.
- No other jobs should be allowed to execute on the processors that are being used. If the processors are gang scheduled and there is enough physical memory for all jobs on all processors, this requirement may be relaxed, but we do not recommend doing so without careful study.
- No more than one process should be executed per processor.

Vendor specifications and actual performance often differ considerably, especially in communication latency and bandwidth. Users should make sure that they are using the most efficient BLAS and BLACS available on their system.