System workload

An accurate and complete definition of a system's workload is critical to predicting or understanding its performance.

A difference in workload can cause far more variation in the measured performance of a system than differences in CPU clock speed or random access memory (RAM) size. The workload definition must include not only the type and rate of requests sent to the system, but also the exact software packages and in-house application programs to be executed.

It is important to include the work that a system is doing in the background. For example, if a system contains file systems that are NFS-mounted and frequently accessed by other systems, handling those accesses is probably a significant fraction of the overall workload, even though the system is not officially a server.

A workload that has been standardized to allow comparisons among dissimilar systems is called a benchmark. However, few real workloads duplicate the exact algorithms and environment of a benchmark. Even industry-standard benchmarks that were originally derived from real applications have been simplified and homogenized to make them portable to a wide variety of hardware platforms. The only valid use for industry-standard benchmarks is to narrow the field of candidate systems that will be subjected to a serious evaluation. Therefore, you should not solely rely on benchmark results when trying to understand the workload and performance of your system.