flux-accounting guide: missing definition(s) for terms

[cmoussa1]

Was perusing the flux-accounting guide this morning and noticed at least one definition missing for fair share. This guide should be stepped through and updated with any other terms that would benefit from having its definition written at the bottom of the guide.

[vsoch]

@cmoussa1 this is a really good idea! I was thinking it would be useful and fun to compare the algorithms we use here with what, for example, a tool like Kueue uses. Can you keep me in the loop?

[cmoussa1]

Sure thing! When you refer to algorithm, are you referring to the algorithm that the flux-accounting priority plugin uses to calculate a job's priority?

[vsoch]

Yep, I would call "fair share" an algorithm but maybe it's not considered one always? https://en.wikipedia.org/wiki/Fair-share_scheduling

[vsoch]

And I'm worried when you say "the algorithm" that's the only one, oh no. 😆

[cmoussa1]

Sorry, maybe I misunderstood you and we are talking about different things! When I refer to fair share as it relates to the flux-accounting priority calculation algorithm, I mean that fair share is one factor of a number of different factors that contribute to how the algorithm calculates priority.

[vsoch]

Interesting! I'd want to ask @grondo @garlick - I'm pretty sure fair share was a scheduling algorithm before it was a factor, and the design here just places it at a different level (to be part of a larger decision process). But I'm guessing it's (mostly?) the same fair share.

[garlick]

In Flux, the priority plugin (in this case provided by flux-accounting) just assigns a priority to each job. The scheduler then takes the priority queue and creates a schedule. So we probably wouldn't call fair share one of our scheduling algorithms. It's just providing input to one.

[vsoch]

But is the underlying logic the same?

[garlick]

Well we're using it for a space shared system as opposed to a time shared one, and it doesn't directly determine the schedule, so that part is not the same. The goal is the same though, to share resources fairly among users or projects as opposed to treating each individual job as an entity that has to be treated fairly.

[vsoch]

Gotcha. So I think if we are working on docs here, we can assume many readers will come with some (even minor) knowledge of what fair share is. Either we will let them make assumptions about our derivative and scope, or (what I think might be best) is we call that out, and then very clearly define the two and explain the difference.