Draft: Add CPU in MHz to stats and emit nomad.client.allocs.cpu.total_mhz metric

[conorevans]

Signed-off-by: Conor Evans coevans@tcd.ie

Resolves #11142

This is a draft PR as I would like to get feedback if I've gone awry. I wasn't sure how the driver.pb.go file gets updated (I see a reference in the makefile but wasn't sure if that gets run as part of PR). I couldn't see any instructions as to regenerating it locally.

[DerekStrickland]

Hi @conorevans

Thanks for this and the other contributions! We'll get them in the pipeline for review!

[tgross]

Hi @conorevans! The overall approach here looks ok.

If you have buf installed (as per make depsor justgo install github.com/bufbuild/buf/cmd/buf@v0.36.0), you can run make proto` and that should regenerate the protobuf file. Once that's done we can review the implementation in detail.

I'm a little concerned about how showing MHz works in practice given CPU frequency scaling... are we going to be giving users completely misleading metrics? But maybe we can assume that if you're using MHz for your metrics that you also know what's going on with CPU frequency scaling? Not sure.

[hashicorp-cla]

All committers have signed the CLA.

[TrueBrain]

While I was fiddling a bit how to get the MHz as a counter, I noticed this PR. Maybe a silly question, and I might misunderstand the code: but isn't total_ticks already in MHz? TotalTicksAvailable returns cpuTotalTicks which is calculated as cpuTotalTicks = math.Floor(float64(cpuNumCores) * cpuMhzPerCore), which is the same CPUMHzTotal returns (minus a Floor)

Mainly I think ticks is a bit ambiguous, as one could think they are jiffies; but they are not.

Again, not that into the Nomad code, so might misunderstand things, but just wanted to leave this here :)

(I mainly ask, as the test-case shows something different, and I couldn't figure out why :P So that is why I am guessing I might be misunderstanding something here)

[tgross]

Yeah I think you're right there @TrueBrain. Let's get your PR #17579 in to get this done.