DRA: add ResourceSlice tracker

The purpose of the tracker is to emulate a ResourceSlice informer, including
cache and event handlers. In contrast to that informer, the tracker adds taints
from a DeviceTaint such that they appear in the ResourceSlice device
definition. Code using the tracker doesn't need to care where the taints are
coming from.

The main advantage is that it enables fine-grained reactions to taints that
only affect a few devices, the common case. Without this tracker, the pod
eviction controller would have to sync all pods when any slice or any taint
change.

In the scheduler it avoids re-evaluating the selection criteria repeatedly.
The tracker serves as a cross-pod-scheduling cache.

Author: nojnhuh

staging/src/k8s.io/dynamic-resource-allocation/internal/queue/fifo.go

@@ -0,0 +1,112 @@
+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// TODO: This is duplicated from ./pkg/scheduler/util/queue because that
+// package is not allowed to be imported here.
+package queue
+
+const (
+	// normalSize limits the size of the buffer that is kept
+	// for reuse.
+	normalSize = 4
+)
+
+// FIFO implements a first-in-first-out queue with unbounded size.
+// The null FIFO is a valid empty queue.
+//
+// Access must be protected by the caller when used concurrently by
+// different goroutines, the queue itself implements no locking.
+type FIFO[T any] struct {
+	// elements contains a buffer for elements which have been
+	// pushed and not popped yet. Two scenarios are possible:
+	// - one chunk in the middle (start <= end)
+	// - one chunk at the end, followed by one chunk at the
+	//   beginning (end <= start)
+	//
+	// start == end can be either an empty queue or a completely
+	// full one (with two chunks).
+	elements []T
+
+	// len counts the number of elements which have been pushed and
+	// not popped yet.
+	len int
+
+	// start is the index of the first valid element.
+	start int
+
+	// end is the index after the last valid element.
+	end int
+}
+
+func (q *FIFO[T]) Len() int {
+	return q.len
+}
+
+func (q *FIFO[T]) Push(element T) {
+	size := len(q.elements)
+	if q.len == size {
+		// Need larger buffer.
+		newSize := size * 2
+		if newSize == 0 {
+			newSize = normalSize
+		}
+		elements := make([]T, newSize)
+		if q.start == 0 {
+			copy(elements, q.elements)
+		} else {
+			copy(elements, q.elements[q.start:])
+			copy(elements[len(q.elements)-q.start:], q.elements[0:q.end])
+		}
+		q.start = 0
+		q.end = q.len
+		q.elements = elements
+		size = newSize
+	}
+	if q.end == size {
+		// Wrap around.
+		q.elements[0] = element
+		q.end = 1
+		q.len++
+		return
+	}
+	q.elements[q.end] = element
+	q.end++
+	q.len++
+}
+
+func (q *FIFO[T]) Pop() (element T, ok bool) {
+	if q.len == 0 {
+		return
+	}
+	element = q.elements[q.start]
+	q.start++
+	if q.start == len(q.elements) {
+		// Wrap around.
+		q.start = 0
+	}
+	q.len--
+
+	// Once it is empty, shrink down to avoid hanging onto
+	// a large buffer forever.
+	if q.len == 0 && len(q.elements) > normalSize {
+		q.elements = make([]T, normalSize)
+		q.start = 0
+		q.end = 0
+	}
+
+	ok = true
+	return
+}

staging/src/k8s.io/dynamic-resource-allocation/internal/queue/fifo_test.go

@@ -0,0 +1,117 @@
+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package queue
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func verifyPop(t *testing.T, expectedValue int, expectedOk bool, queue *FIFO[int]) {
+	t.Helper()
+	actual, ok := queue.Pop()
+	require.Equal(t, expectedOk, ok)
+	require.Equal(t, expectedValue, actual)
+}
+
+func verifyEmpty(t *testing.T, queue *FIFO[int]) {
+	t.Helper()
+	require.Equal(t, 0, queue.Len())
+	verifyPop(t, 0, false, queue)
+}
+
+func TestNull(t *testing.T) {
+	var queue FIFO[int]
+	verifyEmpty(t, &queue)
+}
+
+func TestOnePushPop(t *testing.T) {
+	var queue FIFO[int]
+
+	expected := 10
+	queue.Push(10)
+	require.Equal(t, 1, queue.Len())
+	verifyPop(t, expected, true, &queue)
+	verifyEmpty(t, &queue)
+}
+
+// Pushes some elements, pops all of them, then the same again.
+func TestWrapAroundEmpty(t *testing.T) {
+	var queue FIFO[int]
+
+	for i := 0; i < 5; i++ {
+		queue.Push(i)
+	}
+	require.Equal(t, 5, queue.Len())
+	for i := 0; i < 5; i++ {
+		verifyPop(t, i, true, &queue)
+	}
+	verifyEmpty(t, &queue)
+
+	for i := 5; i < 10; i++ {
+		queue.Push(i)
+	}
+	for i := 5; i < 10; i++ {
+		verifyPop(t, i, true, &queue)
+	}
+	verifyEmpty(t, &queue)
+}
+
+// Pushes some elements, pops one, adds more, then pops all.
+func TestWrapAroundPartial(t *testing.T) {
+	var queue FIFO[int]
+
+	for i := 0; i < 5; i++ {
+		queue.Push(i)
+	}
+	require.Equal(t, 5, queue.Len())
+	verifyPop(t, 0, true, &queue)
+
+	for i := 5; i < 10; i++ {
+		queue.Push(i)
+	}
+	for i := 1; i < 10; i++ {
+		verifyPop(t, i, true, &queue)
+	}
+	verifyEmpty(t, &queue)
+}
+
+// Push an unusual amount of elements, pop all, and verify that
+// the FIFO shrinks back again.
+func TestShrink(t *testing.T) {
+	var queue FIFO[int]
+
+	for i := 0; i < normalSize*2; i++ {
+		queue.Push(i)
+	}
+	require.Equal(t, normalSize*2, queue.Len())
+	require.LessOrEqual(t, 2*normalSize, len(queue.elements))
+
+	// Pop all, should be shrunken when done.
+	for i := 0; i < normalSize*2; i++ {
+		verifyPop(t, i, true, &queue)
+	}
+	require.Equal(t, 0, queue.Len())
+	require.Len(t, queue.elements, normalSize)
+
+	// Still usable after shrinking?
+	queue.Push(42)
+	verifyPop(t, 42, true, &queue)
+	require.Equal(t, 0, queue.Len())
+	require.Len(t, queue.elements, normalSize)
+}