Replace NodeOrder with BestNode

[k82cn]

Is this a BUG REPORT or FEATURE REQUEST?:

/kind feature

Description:

Currently, we're using similar way with upstream to sort nodes for a task to get the best node; but the sort action is not necessary as we just want to get the best node after predicates. It's better to get best node directly instead of sort, the time complexity will be reduced from O(nlogn) to O(n).

[hex108]

If the best node doest not fits, we need pick next one, so will it be better to return a PriorityQueue?

[k82cn]

why best node does not fit after predicates?

[hex108]

@k82cn If I understand correctly, the predicates does not contain resource predicates, so there is some resource compare logic in https://github.com/kubernetes-sigs/kube-batch/blob/master/pkg/scheduler/actions/allocate/allocate.go#L168. Need we enhance the prediates?

Another situation: administrator perhaps does not enable predicate plugin.

[k82cn]

Need we enhance the prediates?

yes, refer to #694 .

Another situation: administrator perhaps does not enable predicate plugin.

Yes, but scheduler can not do anything to enhance that even we have a ordered list :)

[hex108]

Need we enhance the prediates?

yes, refer to #694 .

Thanks for it!

Another situation: administrator perhaps does not enable predicate plugin.

Yes, but scheduler can not do anything to enhance that even we have a ordered list :)

There is resource predicate in https://github.com/kubernetes-sigs/kube-batch/blob/master/pkg/scheduler/actions/allocate/allocate.go#L168. If we fix #694, we could delete those code. However after we add resource predicate in predicates, if there are no nodes satisfying the task, we will try to allocate for next job and we could not pipeline task(it works like reserving resource), big tasks might starve.

[k82cn]

If we fix #694, we could delete those code.

In resource predicates, we need to check both idel & releasing to avoid duplicated preemption; the logic is necessary here as the action maybe different when using resources.

[hex108]

/assign

[k82cn]

btw, we only need this in allocate action.