Updated the scheduler framework's PreFilter interface to return a PreFilterResult

pkg/scheduler/framework/interface.go

@@ -30,6 +30,7 @@ import (
 	"github.com/google/go-cmp/cmp/cmpopts"
 	v1 "k8s.io/api/core/v1"
 	"k8s.io/apimachinery/pkg/types"
+	"k8s.io/apimachinery/pkg/util/sets"
 	"k8s.io/client-go/informers"
 	clientset "k8s.io/client-go/kubernetes"
 	restclient "k8s.io/client-go/rest"
@@ -337,8 +338,10 @@ type PreFilterExtensions interface {
 type PreFilterPlugin interface {
 	Plugin
 	// PreFilter is called at the beginning of the scheduling cycle. All PreFilter
-	// plugins must return success or the pod will be rejected.
-	PreFilter(ctx context.Context, state *CycleState, p *v1.Pod) *Status
+	// plugins must return success or the pod will be rejected. PreFilter could optionally
+	// return a PreFilterResult to influence which nodes to evaluate downstream. This is useful
+	// for cases where it is possible to determine the subset of nodes to process in O(1) time.
+	PreFilter(ctx context.Context, state *CycleState, p *v1.Pod) (*PreFilterResult, *Status)
 	// PreFilterExtensions returns a PreFilterExtensions interface if the plugin implements one,
 	// or nil if it does not. A Pre-filter plugin can provide extensions to incrementally
 	// modify its pre-processed info. The framework guarantees that the extensions
@@ -498,7 +501,9 @@ type Framework interface {
 	// *Status and its code is set to non-success if any of the plugins returns
 	// anything but Success. If a non-success status is returned, then the scheduling
 	// cycle is aborted.
-	RunPreFilterPlugins(ctx context.Context, state *CycleState, pod *v1.Pod) *Status
+	// It also returns a PreFilterResult, which may influence what or how many nodes to
+	// evaluate downstream.
+	RunPreFilterPlugins(ctx context.Context, state *CycleState, pod *v1.Pod) (*PreFilterResult, *Status)
 
 	// RunPostFilterPlugins runs the set of configured PostFilter plugins.
 	// PostFilter plugins can either be informational, in which case should be configured
@@ -608,6 +613,36 @@ type Handle interface {
 	Parallelizer() parallelize.Parallelizer
 }
 
+// PreFilterResult wraps needed info for scheduler framework to act upon PreFilter phase.
+type PreFilterResult struct {
+	// The set of nodes that should be considered downstream; if nil then
+	// all nodes are eligible.
+	NodeNames sets.String
+}
+
+func (p *PreFilterResult) AllNodes() bool {
+	return p == nil || p.NodeNames == nil
+}
+
+func (p *PreFilterResult) Merge(in *PreFilterResult) *PreFilterResult {
+	if p.AllNodes() && in.AllNodes() {
+		return nil
+	}
+
+	r := PreFilterResult{}
+	if p.AllNodes() {
+		r.NodeNames = sets.NewString(in.NodeNames.UnsortedList()...)
+		return &r
+	}
+	if in.AllNodes() {
+		r.NodeNames = sets.NewString(p.NodeNames.UnsortedList()...)
+		return &r
+	}
+
+	r.NodeNames = p.NodeNames.Intersection(in.NodeNames)
+	return &r
+}
+
 type NominatingMode int
 
 const (