Merge pull request #57478 from misterikkit/noArrayGrow

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Avoid array growth in FilteredList

**What this PR does / why we need it**:

The method (*schedulerCache).FilteredList builds an array of *v1.Pod
that contains every pod in the cluster except for those filtered out by
a predicate. Today, it starts with a nil slice and appends to it.

Based on current usage, FilteredList is expected to return every pod in
the cluster or omit some pods from a single node. This change reserves
array capacity equal to the total number of pods in the cluster.

This is a set of 3 PRs targeting affinity predicate performance. (#57476, #57477, #57478) The key takeaway is approximately 2x speedup in the large affinity benchmark.

The unexpected increase in BenchmarkScheduling/1000Nodes/1000Pods seems to be an outlier, and did not recur on subsequent runs. The benchmarks have a moderate amount of variance to them, and I did not run them enough times to measure mean and standard deviation.

| test | b.N | master | #57476 | #57477 | #57478 | combined |
| ---- | --- | ------ | ------ | ------ | ---------- | -------- |
| BenchmarkScheduling/100Nodes/0Pods                | 100 |  39629010 ns/op | 36898566 ns/op (-6.89%)   |  38461530 ns/op (-2.95%)  |  36214136 ns/op (-8.62%)  |  43090781 ns/op (+8.74%)  |
| BenchmarkScheduling/100Nodes/1000Pods             | 100 |  85489577 ns/op | 69538016 ns/op (-18.66%)  |  70104254 ns/op (-18.00%) |  75015585 ns/op (-12.25%) |  80986960 ns/op (-5.27%)  |
| BenchmarkScheduling/1000Nodes/0Pods               | 100 | 219356660 ns/op | 200149051 ns/op (-8.76%)  | 192867469 ns/op (-12.08%) | 196896770 ns/op (-10.24%) | 212563662 ns/op (-3.10%)  |
| BenchmarkScheduling/1000Nodes/1000Pods            | 100 | 380368238 ns/op | 381786369 ns/op (+0.37%)  | 387224973 ns/op (+1.80%)  | 417974358 ns/op (+9.89%)  | 411140230 ns/op (+8.09%)  |
| BenchmarkSchedulingAntiAffinity/500Nodes/250Pods  | 250 | 124399176 ns/op | 97568988 ns/op (-21.57%)  | 112027363 ns/op (-9.95%)  | 129134326 ns/op (+3.81%)  |  98607941 ns/op (-20.73%) |
| BenchmarkSchedulingAntiAffinity/500Nodes/5000Pods | 250 | 491677096 ns/op | 441562422 ns/op (-10.19%) | 278127757 ns/op (-43.43%) | 447355609 ns/op (-9.01%)  | 226310721 ns/op (-53.97%) |

Combined performance contains all three patches.
Percentages are relative to master.

Methodology:

I ran the tests on each branch with this command.
```
make test-integration WHAT="./test/integration/scheduler_perf" KUBE_TEST_ARGS="-run=xxxx -bench=."
```

The benchmarks have a fair amount of variance to them, and I did not run them enough times to measure mean and standard deviation.

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #

The three PRs in this set should collectively fix #54189.

**Special notes for your reviewer**:

**Release note**:

```release-note
Improve scheduler performance of MatchInterPodAffinity predicate.
```

plugin/pkg/scheduler/schedulercache/cache.go

@@ -104,7 +104,14 @@ func (cache *schedulerCache) List(selector labels.Selector) ([]*v1.Pod, error) {
 func (cache *schedulerCache) FilteredList(podFilter PodFilter, selector labels.Selector) ([]*v1.Pod, error) {
 	cache.mu.Lock()
 	defer cache.mu.Unlock()
-	var pods []*v1.Pod
+	// podFilter is expected to return true for most or all of the pods. We
+	// can avoid expensive array growth without wasting too much memory by
+	// pre-allocating capacity.
+	maxSize := 0
+	for _, info := range cache.nodes {
+		maxSize += len(info.pods)
+	}
+	pods := make([]*v1.Pod, 0, maxSize)
 	for _, info := range cache.nodes {
 		for _, pod := range info.pods {
 			if podFilter(pod) && selector.Matches(labels.Set(pod.Labels)) {