CPU Usage

At a given point in time, CPU Usage describes the level of utilisation of the system CPU(s), broken down into four states.

IO Wait
Indicates the proportion of CPU cycles spent waiting for IO (disk or network) events. If you experience large IO Wait proportions, it can indicate that your disks are causing a performance bottleneck.

This is known as being IO Bound. To solve this issue, first attempt to optimize your applications disk usage (e.g. caching, delayed writes). From that point, you may need to look at improving disk performance directly through faster drives and/or RAID arrays. (More on Disk IO)

System
Indicates the proportion of CPU cycles spent performing kernel-level processing. Generally you will find only a small proportion of your CPU cycles are spent on system tasks, hence if you see spikes it could indicate a problem. Software RAID setups undergoing rebuild can cause high system CPU consumption.

User
Indicates the proportion of CPU cycles spent performing user instigated processing. This is where you should see the bulk of your CPU cycles consumed; it includes activities such as web serving, application execution, and every other process not owned by the kernel.

You should expect your web server to show User CPU level fluctutations throughout the day as traffic levels vary.

Idle
Indicates the spare CPU capacity you have - all the cycles where the CPU is, quite literally, doing nothing.

Performance Graphs

 

See Also

• Server Health Monitoring
• Linux Server Health Monitoring
• Application Monitor - Web Edition - Datasheet