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KEP: Add local queue weight #963

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1 change: 1 addition & 0 deletions apis/kueue/v1beta1/clusterqueue_types.go
Original file line number Diff line number Diff line change
Expand Up @@ -241,6 +241,7 @@ const (
PreemptionPolicyAny PreemptionPolicy = "Any"
PreemptionPolicyLowerPriority PreemptionPolicy = "LowerPriority"
PreemptionPolicyLowerOrNewerEqualPriority PreemptionPolicy = "LowerOrNewerEqualPriority"
PreemptionPolicyOverWeight PreemptionPolicy = "OverWeight"
)

// ClusterQueuePreemption contains policies to preempt Workloads from this
Expand Down
369 changes: 369 additions & 0 deletions keps/752-localqueue-weight/README.md
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# KEP-752: Support Weight in localQueue for better resource partitioning

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<!-- toc -->
- [KEP-752: Support Weight in localQueue for better resource partitioning](#kep-752-support-weight-in-localqueue-for-better-resource-partitioning)
- [Summary](#summary)
- [Motivation](#motivation)
- [Goals](#goals)
- [Non-Goals](#non-goals)
- [Proposal](#proposal)
- [User Stories (Optional)](#user-stories-optional)
- [Story 1](#story-1)
- [Notes/Constraints/Caveats (Optional)](#notesconstraintscaveats-optional)
- [Risks and Mitigations](#risks-and-mitigations)
- [Design Details](#design-details)
- [API](#api)
- [Support Weight in localQueue](#support-weight-in-localqueue)
- [Local Queue Filtering and Sorting Policy Interface](#local-queue-filtering-and-sorting-policy-interface)
- [Extension Points in Cluster Queue](#extension-points-in-cluster-queue)
- [Test Plan](#test-plan)
- [Prerequisite testing updates](#prerequisite-testing-updates)
- [Unit Tests](#unit-tests)
- [Integration tests](#integration-tests)
- [Graduation Criteria](#graduation-criteria)
- [Implementation History](#implementation-history)
- [Drawbacks](#drawbacks)
- [Alternatives](#alternatives)
<!-- /toc -->

## Summary

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Add a extension point to determine whether a workload in certain local queue can
be scheduled.

## Motivation

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Currently, for queues inside one CQ, we can submit queues as much as we want until the bottleneck of CQ, and one queue can occupy the whole resources with higher priorities. A limitation for a local queue is helpful for resource partitioning.
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IMHO, there are two options here:

  • stay with 2 level hierarchy that Kueue offers today - have each local queue point to a different cluster queue with some resources, and allow some borrowing/eviction between queues via cohorts.
  • explicitly introduce multi-level hierarchy

This KEP is somewhere between the two - introduces 3 level hierarchy, but with a different functionality set on level 1 (local queues in cluster queue) and level 2 (cluster queues in a cohort).

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To Marcin's point, one thing to consider is that LocalQueues are namespaced. As such, it means that administrators could only define weights between users that are in the same namespace.

This could be quite limiting for some organizations that requires a namespace for each end-user.

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Sorry maybe I didn't totally understand u. Do you mean maybe we should consider adding weight on cluster queues instead of local queues?

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I think weight in local queue is a resource consumption policy to control whose priority is more higher when scheduling and the resources in the queue will not be further segmented. We will still stay with 2 level hierarchy that Kueue offers today.

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Today, fair sharing and borrowing semantics happen for CQs within a cohort.

By adding weight to LQs, we are adding fair sharing to that level, implicitly adding one more level of hierarchy. The question is: do we want to do that, or should we rather implement arbitrary hierarchies where CQs can belong to other CQs or Cohort is an CRD and cohorts can belong to cohorts.

I'm not saying that one option or the other is better. I'm saying that we need to ponder all the options. Kueue APIs offer backwards compatibility, meaning that if we add an API, we need to maintain it forever or offer a deprecation process.

To Marcin's point, one thing to consider is that LocalQueues are namespaced. As such, it means that administrators could only define weights between users that are in the same namespace.
This could be quite limiting for some organizations that requires a namespace for each end-user.

Nvm about that comment. I realize it's wrong as multiple namespaces can point to the same CQ and we could respect weight among them.

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Thanks for explain!
In my cloud scene, my customers will create a quota node for each department and create a leaf quota node for each user, each user will have their own namespace to submit workloads. Unused resources will be shared by users by min and max like elastic quota in scheduler-plugins.
So I think maybe a 3 level tree is enough for the cases.

I have three ideas.

  1. Add a crd to define weights for local queues in a certain namespace and allow users to create and modify the resource may meet the requirement of Abdullah. But will still add one more level of hierarchy.

  2. Allow admin to define parent cluster queue in cluster queue's spec. Cohort can only be set for the cluster queues who have same parent. Sum nominal resources of Children CQ must less than parent CQ's nominal resources. In this case, the functions in this KEP can be converted into multi-level CQ. But because users can not create and modify cluster queue, users will not be able to manage different workloads' resource consumption of their own.

  3. Combine 1 and 2.

HDYT?

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@alculquicondor @ahg-g Hi, if u have time, please take a look and let me know your options, I will continue work on this issue, thank very much. :D

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I think the better approach would be something along the lines of 2, which is also similar to #79

And here we have two high level alternatives:
a. Make a cohort a CRD. Then you could make cohorts be part of other cohorts. In this case, cohorts themselves don't have quota (like today). But they could still have weights, that only have semantics around borrowing.
b. Make CQs either belong to a cohort (today's mode) or another CQ. In this case, the child CQ cannot have limits, but can only have weights.

It might be useful to look into how systems like YARN or Slurm do multi-level hierarchy.

Question about your use-case: why not create a cohort per department and one CQ per user?

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Also #62 is related.

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Ok, thanks, if there is any progress, I will add it on KEP


### Goals

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List the specific goals of the KEP. What is it trying to achieve? How will we
know that this has succeeded?
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- Define an interface which supports local queues filtering and sorting
- Implement a policy to filter and sort the local queue based on the queue usage and local queue's weight

### Non-Goals

- Use min-max to guarantee the resources.

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## Proposal

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### User Stories (Optional)

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#### Story 1

As a tenant, I wish each tenant's workload should be scheduled fairly. No one
can occupy the whole cluster queue by submiting a lot of workloads or seting all his
workloads as highest level.

### Notes/Constraints/Caveats (Optional)

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## Design Details

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### API

We add a new CRD named `CoHort` to define the details about a `cohort`.
```golang
type CoHortSpec struct {
Name string
ParentCQ string
}
type CoHortStatus struct {
Usage []FlavorUsage
}
```

If a `CoHort` belongs to any ClusterQueue, sum of the nominal resources
for CQs with `CQ.cohort=CoHort.name` must less or equal than the nominal
resources of the parent cluster queue.

We will prevent any local queue point to a parent cluster queue to only
allow submitting workloads to leaf cluster queues.

And we will add a weight property in local queue to allow setting weights.
We will allow users to change the property, and use `XValidation` to prevent
from users to change cluster queue field.

Weight will be effective for all local queues point to same cluster queue.
If someone only need to fine tune resource sharing between his/her workloads, admins
will create a cluster queue for his/her namespace, and create multi local queue
for him/her. So that he/she can meet the goal.
```golang
// LocalQueueSpec defines the desired state of LocalQueue
type LocalQueueSpec struct {
// +kubebuilder:validation:XValidation:rule="self == oldSelf",message="Value is immutable"
ClusterQueue ClusterQueueReference `json:"clusterQueue,omitempty"`
weight *int
}
```

In this way, our users can fine tune resource sharing between their workloads, and admins
can offer multi-level hierarchy for their users.

We add a knob in cluster queue to allow users choose local queue sort and filter plugin.
```golang
type Plugin string
const Fairness Plugin = "fairness"
const None Plugin = "none"

type PluginConfig struct {
Name string
Args map[string]interface{}
}

// ClusterQueueSpec defines the desired state of ClusterQueue
type ClusterQueueSpec struct {
...
LocalQueueFilterPlugin Plugin
LocalQueueSortPlugin Plugin
PluginConfig PluginConfig
}
```

We add an option in `ClusterQueuePreemption` to allow users set preemption policy when
local queue use too much resources. When we set `WithinClusterQueue` to `PreemptionPolicyExceedWeight`,
we will preempt from those local queues whose usage exceed their weight.

```golang
const PreemptionPolicyExceedWeight PreemptionPolicy = "ExceedWeight"
```

### Support Weight in localQueue

We maintain current weight for each queue. We will reject the head workload
in a local queue whose current weight is greater than desired weight and then
sort local queues in a cluster queue based on their current weights.
We use the dominant resource to calculate the current weight.

We calculate current weight for each queue based on the following method:
```
totalResources = sum of all admitted workloads
currentWeight = map[stirng]int64
for lq in cq:
drfWeight = 0
for resName, resCount in lq.Res:
calculate resCount/totalResources[resName]
if resCount/totalResources[resName] > drfWeight:
drfWeight = resCount/totalResources[resName]
currentWeight[lq.Name] = drfWeight
return currentWeight
```

### Local Queue Filtering and Sorting Policy Interface

```golang

type Plugin interface {
Name() string
}

type LocalQueueSortPlugin interface {
Plugin
Less(cq ClusterQueue, lqs []LocalQueue, i, j int) int
}

type LocalQueueFilteringPlugin interface {
Plugin
Filter(cq ClusterQueue, lqs []LocalQueue, i int) Status
}

```

### Extension Points in Cluster Queue

We will modify `entryOrdering` to support local queue sort plugins and modify `Manager.Heads` to support local queue
filter plugins.

Besides, we will modify `preemptor` to preempt workloads if local queue's usage exceed its weight.

### Test Plan

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##### Prerequisite testing updates

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## Implementation History

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## Drawbacks

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## Alternatives

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18 changes: 18 additions & 0 deletions keps/752-localqueue-weight/kep.yaml
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title: Support Weight in localQueue for better resource partitioning
kep-number: 752
authors:
- "@KunWuLuan"
status:
creation-date: 2023-06-13
reviewers:
- "@alculquicondor"
- "@kerthcet"
approvers:

# The target maturity stage in the current dev cycle for this KEP.
stage: alpha|beta|stable

# The most recent milestone for which work toward delivery of this KEP has been
# done. This can be the current (upcoming) milestone, if it is being actively
# worked on.
latest-milestone: "v0.5"