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New CPU Usage Plugin

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Eric Lindvall of Cloudvox has created a CPU Usage plugin for the Scout directory.

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.

Different from Server Load

Note that this plugin is distinct from the Server Load plugin. For information on load averages, see our understanding load averages post from last year.

Thanks again to Eric Lindvall of Cloudvox. As always, drop us a note at support@scoutapp.com if you have questions.

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