diskio plugin runs udevadm every time

[propertone]

In #3663, @danielnelson implied that the diskio plugin does NOT run udevadm directly, but it's actually running the udevadm command every interval for each device. We have a system with hundreds of disks/partitions and the diskio plugin takes several seconds to run because of this.

Relevant telegraf.conf:

[[inputs.diskio]]
    # default configuration

System info:

Telegraf: v1.6.1 (git: release-1.6 bf0ab27)
Linux: RedHat 7.5
Kernel: 3.10.0-693.21.1.el7.x86_64

Steps to reproduce:

1. Run telegraf with the diskio plugin using the default configuration
2. Use lastcomm to see that it's actually running udevadm every time

Expected behavior:

udevadm is not run at all, or at least cached

Actual behavior:

udevadm command is run every interval for each disk. Its output is not used as #3663 is still an issue.

[danielnelson]

I think I mentioned this behavior in this comment:

the function we call on each interval in gopsutil already runs this udevadm command for each device found without caching to get the serial number

The good news is this has already been addressed in gopsutil, which should improve the performance quite a bit.

[propertone]

Oops, I missed that. Thanks!

[danielnelson]

The updated gopsutil release that does not run udevadm has been merged, so this change will be in 1.8.