Wormly Metrics provides CPU Usage monitoring - among thousands of other metrics.
At a given point in time, CPU Usage describes the level of utilisation of the system CPU(s), broken down into three states.
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, SSD, and/or RAID arrays. (More on Disk IO)
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.
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 fluctuations throughout the day as traffic levels vary.
Idle (not shown)
Indicates the spare CPU capacity you have - all the cycles where the CPU is, quite literally, doing nothing. It is omitted from the graph as it simply corresponds to the blank area above the other three components.