[karmakaze]

Yeah, I don't see how deadlines/SLOs does any better when there's insufficient capacity to meet those of queued jobs at their concurrency.

> I don’t think it’s possible to meet a latency target through prioritization when there is a fundamental lack of capacity.

This seemingly implies that it would be achievable with target deadlines/SLOs. At capacity I don't see a better solution than give each priority (or target latency) a defined minimum resource allocation.

[arakageeta]

Under deadline scheduling, every pending job _eventually_ has highest priority as time elapses. (Assuming new jobs can’t arrive with deadlines in the past.) Every job is eventually serviced.

The “pain” experienced in an overload situations is spread among all late jobs. Contrast this with fixed-priority scheduling, where lowest priority jobs will be starved completely, until the overload is resolved.

[karmakaze]

That's where I was saying in the case of insufficient capacity, the available capacity is divided among the priorities in non-equal but non-zero portions. The SLO/deadline method effectively would be doing something similar as everything would be overdue and the most overdue get highest priority to run. The only difference is that the there's no unequal portioning unless there's additional logic to say x overdue of job A is more important than x overdue of job B, which amounts to setting priorities in the end.

[Dylan16807]

> The “pain” experienced in an overload situations is spread among all late jobs. Contrast this with fixed-priority scheduling, where lowest priority jobs will be starved completely, until the overload is resolved.

Though this is often not a good way to spread out the pain.

It's probably much worse for the 15s job to be a minute late than for the 8h job to be a minute late, but basic deadline scheduling will treat them the same. So you want sharing, but uneven sharing.