Microprocessor report

The microprocessor statistics columns (% user, % sys, % idle, and % iowait) provide a breakdown of microprocessor usage.

This information is also reported in the vmstat command output in the columns labeled us, sy, id, and wa. For a detailed explanation for the values, see vmstat command. Also note the change made to % iowait described in Wait I/O time reporting.

On systems running one application, high I/O wait percentage might be related to the workload. On systems with many processes, some will be running while others wait for I/O. In this case, the % iowait can be small or zero because running processes "hide" some wait time. Although % iowait is low, a bottleneck can still limit application performance.

If the iostat command indicates that a microprocessor-bound situation does not exist, and % iowait time is greater than 20 percent, you might have an I/O or disk-bound situation. This situation could be caused by excessive paging due to a lack of real memory. It could also be due to unbalanced disk load, fragmented data or usage patterns. For an unbalanced disk load, the same iostat report provides the necessary information. But for information about file systems or logical volumes, which are logical resources, you must use tools such as the filemon or fileplace commands.