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https://issues.apache.org/jira/browse/YUNIKORN-3463?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Hedger Lai updated YUNIKORN-3463:
---------------------------------
Summary: [Core] Premature loop abort in calculateAdditionalVictims starves
preemption (was: [Core] Premature loop abort and missing satisfaction
early-stop in calculateAdditionalVictims)
> [Core] Premature loop abort in calculateAdditionalVictims starves preemption
> ----------------------------------------------------------------------------
>
> Key: YUNIKORN-3463
> URL: https://issues.apache.org/jira/browse/YUNIKORN-3463
> Project: Apache YuniKorn
> Issue Type: Bug
> Components: core - scheduler
> Reporter: Hedger Lai
> Assignee: Hedger Lai
> Priority: Major
> Fix For: 1.6.0
>
>
> h3. Symptom
> In {{Preemptor.calculateAdditionalVictims()}}, preemption for queue quota
> exhibits two loop control defects:
> 1. If an early candidate victim cannot fit in the ask queue's remaining
> guaranteed headroom, the loop executes a raw {{break}}, prematurely aborting
> the search and starving subsequent viable victims.
> 2. Conversely, when accumulated victims have already satisfied the ask
> queue's guaranteed quota, the loop fails to exit early, scanning remaining
> victims unnecessarily.
> h3. Root Cause
> In {{pkg/scheduler/objects/preemption.go}}:
> {code:go}
> askQueueRemaining := askQueue.GetRemainingGuaranteedResource()
> if askQueueRemaining != nil &&
> askQueueRemaining.FitInActual(victim.GetAllocatedResource()) {
> askQueue.AddAllocation(victim.GetAllocatedResource())
> } else {
> queueSnapshot.AddAllocation(victim.GetAllocatedResource())
> break // <-- Flaw 1: premature abort on fit failure
> }
> // ...
> // Flaw 2: missing early-stop when quota is already satisfied
> {code}
> h3. Proposed Fix
> 1. In the {{else}} branch of {{FitInActual()}}, replace {{break}} with
> {{continue}} to evaluate subsequent viable candidates.
> 2. After appending a valid victim, {{break}} immediately if
> {{isAskQueueUnderGuaranteed()}} is satisfied.
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