Section 2.3. CPU Utilization

2.3. CPU Utilization

You can calculate CPU utilization from vmstat by subtracting id from 100 or by adding us and sy. Keep in mind the following points when considering CPU utilization.

• 100% utilized may be fineit can be the price of doing business.

• When a Solaris system hits 100% CPU utilization, there is no sudden dip in performance; the performance degradation is gradual. Because of this, CPU saturation is often a better indicator of performance issues than is CPU utilization.

• The measurement interval is important: 5% utilization sounds close to idle; however, for a 60-minute sample it may mean 100% utilization for 3 minutes and 0% utilization for 57 minutes. It is useful to have both short- and long-duration measurements.

• An server running at 10% CPU utilization sounds like 90% of the CPU is available for "free," that is, it could be used without affecting the existing application. This isn't quite true. When an application on a server with 10% CPU utilization wants the CPUs, they will almost always be available immediately. On a server with 100% CPU utilization, the same application will find that the CPUs are already busyand will need to preempt the currently running thread or wait to be scheduled. This can increase latency (which is discussed in more detail in Section 2.11).