How to get CPU usage percentage measured by Collectd in InfluxDB

Question

I'm collecting cpu usage measured in jiffies by Collectd 5.4.0 and then storing the results in InfluxDB 0.9.4. I use the following query to get cpu percentage from InfluxDB:

SELECT MEAN(value) FROM cpu_value WHERE time >= '' and time <= '' GROUP BY type,type_instance

But when I plot the result it makes no sense. There is no pattern in cpu usage. Please let me know If I do something wrong.

Thanks

Answer 1

Since Collectd 5.5 you can get values in percentage instead of jiffies:

<Plugin cpu>
  ReportByState = true
  ReportByCpu = true
  ValuesPercentage = true
</Plugin>

Then you can write query like:

SELECT mean("value") FROM "cpu_value" WHERE 
  "type_instance" =~ /user|system|nice|irq/ 
  AND "type" = 'percent' AND $timeFilter 
  GROUP BY time($interval), "host"

If you can upgrade it might be the easiest option. Otherwise you can:

• precompute percentage on client
• use other client for reporting stats (such as statsd, telegraf, etc.)

With InfluxDB 0.12 you can perform arithmetic operations between fields like:

SELECT MEAN(usage_system) + MEAN(usage_user) AS cpu_total
FROM cpu

However for using this you would have to report from collectd user|system|nice|irq as FIELDS not TAGS.

Answer 2

this is my query, I use it with percent unit (on Axes tab), but stack+percent (on display tab) make sense as well

SELECT non_negative_derivative(mean("value"), 1s) FROM "cpu_value" WHERE "type_instance" =~ /(idle|system|user|wait)/ AND $timeFilter GROUP BY time($interval), "type_instance" fill(null)

The non_nagative_derivative(1s) can be replaced with derivative(1s), I had some of negative value when values was missing.