cpu_dragonfly.go's cpu time doesn't seem to be in second against its name (node_cpu_seconds_total)

[iori-yja]

Host operating system: output of uname -a

DragonFly tech-y09-dfly 5.3-DEVELOPMENT DragonFly v5.3.0.18494.gc70d4-DEVELOPMENT #1: Fri Aug 24 12:27:12 JST 2018 root@tech-y09-dfly:/usr/obj/usr/src/sys/X86_64_GENERIC x86_64

node_exporter version: output of node_exporter --version

Installed from source.
iori@tech-y09-dfly% git log | head -n 3
commit 7519967
Author: Ben Kochie superq@gmail.com
Date: Sat Oct 20 08:21:51 2018 +0200
iori@tech-y09-dfly% node_exporter --version
node_exporter, version (branch: , revision: )
build user:
build date:
go version: go1.10.3

node_exporter command line flags

node_exporter (default)

Are you running node_exporter in Docker?

No

What did you do that produced an error?

Just run.

What did you expect to see?

The node_cpu_seconds_total metrics are in seconds.

What did you see instead?

The total sum of irate of reported metrics are around 40ms which is too smaller than expected (this should be 1 second * ncpu).

The cause

According to cpu_dragonfly.go, the metrics are extracted from kern.cputime and divided by the frequency of kern.cputimer.freq.
However, the comment in the source code states that it counts in microseconds.
https://github.com/DragonFlyBSD/DragonFlyBSD/blob/master/sys/kern/kern_clock.c#L118

The comment is consistent with a shell script as following:

iori@tech-y09-dfly% @ tim=`sysctl kern.cp_time | awk '{print $2 + $3 + $4 + $5 + $6}'` && sleep 1 && @ tim2=`sysctl kern.cp_time | awk '{print $2 + $3 + $4 + $5 + $6}'` ; @ dur = $tim2 - $tim ; echo $dur
4003724

This machine has four cores, so the timer goes around 1000k ticks per CPU in a second, which implies the kernel counts it in microseconds.

I'd like to know why they are divided by that frequency instead of 1/micros.

[discordianfish]

This was introduced in #310 - @stuartnelson3 Can you clarify this? No clue about Drgonflybsd unfortunately..

[stuartnelson3]

I asked that question (a looong time ago 😄 ) on the dfly mailing list:

http://lists.dragonflybsd.org/pipermail/users/2016-September/356968.html

It's something I could have easily done wrong. At the time, it seemed to get the right values on my system, but it could (and seems to) be wrong.

[iori-yja]

Thank you, @stuartnelson3... it is curious that the answer turned out wrong.

I have submitted a Pull request #1140 which works on my machine. I'm happy if you would be kind to check this on your environment.