Feature request: clocksource metrics

[guidoiaquinti]

It could be nice to have node_exporter exposing clocksource metrics.

giaquinti@ubuntu1604:~$ tree /sys/devices/system/clocksource/
/sys/devices/system/clocksource/
├── clocksource0
│   ├── available_clocksource
│   ├── current_clocksource
│   ├── power
│   │   ├── async
│   │   ├── autosuspend_delay_ms
│   │   ├── control
│   │   ├── runtime_active_kids
│   │   ├── runtime_active_time
│   │   ├── runtime_enabled
│   │   ├── runtime_status
│   │   ├── runtime_suspended_time
│   │   └── runtime_usage
│   ├── subsystem -> ../../../../bus/clocksource
│   ├── uevent
│   └── unbind_clocksource
├── power
│   ├── async
│   ├── autosuspend_delay_ms
│   ├── control
│   ├── runtime_active_kids
│   ├── runtime_active_time
│   ├── runtime_enabled
│   ├── runtime_status
│   ├── runtime_suspended_time
│   └── runtime_usage
└── uevent

4 directories, 23 files

[discordianfish]

Seems reasonable in general, curious though: Why are you interested in these metrics? Any particular failure scenario where you'd need them?

[SuperQ]

The current clocksource would be a good info metric. VMs can be switched to different clock types. Internal with hpet, or external like kvm-clock.

[guidoiaquinti]

@discordianfish exactly for what @SuperQ mentioned: we are in the process of rolling out a clocksource change across our EC2 fleet and getting some metric about the clock type usage would be helpful.

From AWS docs:

Hardware Virtual Machine (HVM) instances use a variety of clock sources, such as Xen, Time Stamp Counter (TSC), High Precision Event Time (HPET), or Advanced Configuration and Power Interface Specification (ACPI). Xen is a clock source provided by the Xen virtualization system, and it's the recommended clock source for AWS offerings. Also note that EC2 instances such as C5 or M5 use the AWS Nitro Hypervisor, which uses different clock sources, and the Xen clock might not be available.

ref: https://aws.amazon.com/premiumsupport/knowledge-center/manage-ec2-linux-clock-source/

[pgier]

I can work on adding this to procfs. To start, do we mainly want the contents of available_clocksource and current_clocksource?

[guidoiaquinti]

Thanks for volunteering @pgier! I think we can start with those 2 and maybe add more later if we need to