The plugin uses the same underlying data that vmstat uses in /proc to give you the CPU usage for the full duration between scout runs.
This means the sampling interval for the plugin is equal to your Scout execution interval -- three minutes for an Ultimate account, etc.
Understanding CPU Usage Metrics
The CPU Usage plugin provides the following:
- % System: percentage of time spent in the kernel
- % User: percentage of time in "userland" (your code, apache, mysql, etc)
- % IO Wait: percentage of time waiting for the disk to return data
- number of running processes: processes that are being processed by the CPUs
- number of blocked processes: processes that are waiting for IO (or possibly other things).
- number of interrupts per second
Eric elaborated on the interrupts metric:
The interrupts per second metric is very interesting because it gives you insight into part of what the kernel is doing in the "System" time. Also, many times a high interrupt rate can be an indication of mis-configured hardware like a NIC.
There isn't a single "good value" for number of interrupts/second, Eric explains:
A lot of it depends on the connected devices, their configurations, and the amount of throughput the device is doing.
... however, you can should watch the int interrupts /sec metric after OS changes:
One nice thing this will show you is if your interrupts/sec spikes after a kernel upgrade, one of the upgraded drivers may be doing something bad that it wasn't doing before.