cpu statistics: add dimentions with mode="user|system" insetead of separate counter names?

[flixr]

The cpu metrics were recently split from namedprocess_namegroup_cpu_seconds_total into namedprocess_namegroup_cpu_user_seconds_total and namedprocess_namegroup_cpu_system_seconds_total.
I'm wondering if it wouldn't be nicer to expose them under the old name and add an extra dimension with mode instead (basically like the node_exporter).
Then it would be backwards compatible and easier to extend if we wanted to expose other "modes" later as well...

[ncabatoff]

The only other modes exposed by the kernel on a per-process basis that I can see in proc(5) are guest_time and cguest_time, which I don't really see a compelling use case for.

In terms of backwards compatibility I prefer to drop metrics rather than change their labelsets. I don't like having metrics in Prometheus with a variable number of labels.

I do agree that it would be nicer to have user/system as labels of a metric rather than distinct metrics as they are now, just so you can sum() them. Now I just have to think of a new name for it...

[flixr]

There are also cutime and cstime, not really sure how useful they are though...

[ncabatoff]

Fixed in #84.