kubernetes / kubernetes

What happened?

#119779 added some map queries and creations that add non-negligible latency.

The pprof reveals the following lines inside findNodesThatFitPod as too expensive:

22.2%

kubernetes/pkg/scheduler/schedule_one.go

Line 492 in 44bd04c

diagnosis.NodeToStatusMap[n.Node().Name] = framework.NewStatus(framework.UnschedulableAndUnresolvable, "node is filtered out by the prefilter result")
21.7%

kubernetes/pkg/scheduler/schedule_one.go

Line 489 in 44bd04c

if !preRes.NodeNames.Has(n.Node().Name) {

What did you expect to happen?

Scheduler to keep a throughput of 300 pods/s

How can we reproduce it (as minimally and precisely as possible)?

Schedule 5k daemonset pods giving 300 qps to the scheduler

Anything else we need to know?

No response

Kubernetes version

$ kubectl version
# paste output here

v1.30

Cloud provider

GKE

OS version

# On Linux:
$ cat /etc/os-release
# paste output here
$ uname -a
# paste output here

# On Windows:
C:\> wmic os get Caption, Version, BuildNumber, OSArchitecture
# paste output here

Install tools

Container runtime (CRI) and version (if applicable)

Related plugins (CNI, CSI, ...) and versions (if applicable)

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/sig scheduling

Before #119779, there was this line:
https://github.com/sanposhiho/kubernetes/blob/5ab23179473b621e911511b03693234b60a38033/pkg/scheduler/schedule_one.go#L489

which also had a map access. So we can quite confidently say that the culprit is just the map insert of

kubernetes/pkg/scheduler/schedule_one.go

Line 492 in 44bd04c

    
           diagnosis.NodeToStatusMap[n.Node().Name] = framework.NewStatus(framework.UnschedulableAndUnresolvable, "node is filtered out by the prefilter result")

@sanposhiho, @AxeZhan I have two alternatives:

The obvious one is to do a preallocation for the size of the map. I suspect this might be enough, but still somewhat wasteful.
Change the preemption logic to assume that if a Node is not in the status map, it's UnschedulableAndUnresolvable.

kubernetes/pkg/scheduler/framework/preemption/preemption.go

Line 422 in 44bd04c

if m[name].Code() == framework.UnschedulableAndUnresolvable {

Option 2 also solves #124705. However, external PostFilter plugins need to be aware of the change. But I'm not aware of any in the wild that implements a behavior similar to preemption. We can leave an ACTION REQUIRED. But was this path working in 1.28 and older?

Regardless of the decision, I think we should accompany the fix with an integration test for preemption by daemonset pods.

Can we try (1) first, ask Google for a scalability test again, and then consider (2) if (1) doesn't improve the throughput enough?

(2) could break existing PostFilter plugins. Given PostFilter is not only for preemption, in the world, there may be custom PostFilter plugins which have to rely on the status map with UnschedulableAndUnresolvable nodes. So, it'd be best if we could avoid this breaking.

Since (1) is a really small fix, I'm also thinking if we can run tests after #124714 , and then consider (2) base on the test results.