Add max score picker

pkg/epp/scheduling/plugins/pickers/max-score.go

@@ -0,0 +1,54 @@
+package pickers
+
+import (
+	"fmt"
+
+	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/scheduling/types"
+	logutil "sigs.k8s.io/gateway-api-inference-extension/pkg/epp/util/logging"
+)
+
+// MaxScorePicker picks the pod with the maximum score from the list of
+// candidates.
+type MaxScorePicker struct{}
+
+var _ types.Picker = &MaxScorePicker{}
+
+// Name returns the name of the picker.
+func (msp *MaxScorePicker) Name() string {
+	return "max-score"
+}
+
+// Pick selects the pod with the maximum score from the list of candidates.
+func (msp *MaxScorePicker) Pick(ctx *types.Context, pods []types.Pod) (*types.Result, error) {
+	debugLogger := ctx.Logger.V(logutil.DEBUG).WithName("max-score-picker")
+	debugLogger.Info(fmt.Sprintf("Selecting the pod with the max score from %d candidates: %+v",
+		len(pods), pods))
+
+	winners := make([]types.Pod, 0)
+
+	maxScore := 0.0
+	for _, pod := range pods {
+		score := pod.Score()
+		if score > maxScore {
+			maxScore = score
+			winners = []types.Pod{pod}
+		} else if score == maxScore {
+			winners = append(winners, pod)
+		}
+	}
+
+	if len(winners) == 0 {
+		return nil, nil
+	}
+
+	if len(winners) > 1 {
+		debugLogger.Info(fmt.Sprintf("Multiple pods have the same max score (%f): %+v",
+			maxScore, winners))
+
+		randomPicker := RandomPicker{}
+		return randomPicker.Pick(ctx, winners)
+	}
+
+	debugLogger.Info(fmt.Sprintf("Selected pod with max score (%f): %+v", maxScore, winners[0]))
+	return &types.Result{TargetPod: winners[0]}, nil
+}

pkg/epp/scheduling/plugins/picker.go → pkg/epp/scheduling/plugins/pickers/random.go

@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-package plugins
+package pickers
 
 import (
 	"fmt"
@@ -24,12 +24,17 @@ import (
 	logutil "sigs.k8s.io/gateway-api-inference-extension/pkg/epp/util/logging"
 )
 
+// RandomPicker picks a pod randomly from the list of candidates.
 type RandomPicker struct{}
 
+var _ types.Picker = &RandomPicker{}
+
+// Name returns the name of the picker.
 func (rp *RandomPicker) Name() string {
 	return "random"
 }
 
+// Pick selects a random pod from the list of candidates.
 func (rp *RandomPicker) Pick(ctx *types.Context, pods []types.Pod) (*types.Result, error) {
 	ctx.Logger.V(logutil.DEBUG).Info(fmt.Sprintf("Selecting a random pod from %d candidates: %+v", len(pods), pods))
 	i := rand.Intn(len(pods))

pkg/epp/scheduling/scheduler.go

@@ -26,6 +26,7 @@ import (
 	backendmetrics "sigs.k8s.io/gateway-api-inference-extension/pkg/epp/backend/metrics"
 	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/metrics"
 	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/scheduling/plugins"
+	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/scheduling/plugins/pickers"
 	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/scheduling/types"
 	logutil "sigs.k8s.io/gateway-api-inference-extension/pkg/epp/util/logging"
 )
@@ -74,7 +75,7 @@ func NewScheduler(datastore Datastore) *Scheduler {
 		postSchedulePlugins: []types.PostSchedule{},
 		scorers:             []types.Scorer{},
 		filters:             []types.Filter{defaultPlugin},
-		picker:              defaultPlugin,
+		picker:              &pickers.MaxScorePicker{},
 	}
 }
 
@@ -198,7 +199,7 @@ func runScorersForPod(ctx *types.Context, scorers []types.Scorer, pod types.Pod)
 }
 
 type defaultPlugin struct {
-	plugins.RandomPicker
+	pickers.RandomPicker
 }
 
 func (p *defaultPlugin) Name() string {

pkg/epp/scheduling/types/interfaces.go

@@ -63,6 +63,7 @@ type Filter interface {
 }
 
 // Scorer defines the interface for scoring pods based on context.
+// Scorers must return a score between 0 and 1, where 1 is the best score.
 type Scorer interface {
 	Plugin
 	Score(ctx *Context, pod Pod) (float64, error)