Strategy: Set threshold priority from strategy's parameters

pkg/utils/priority.go

@@ -1,9 +1,15 @@
 package utils
 
 import (
+	"context"
+	"fmt"
+
 	v1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/labels"
 	"k8s.io/apimachinery/pkg/util/sets"
+	clientset "k8s.io/client-go/kubernetes"
+	"sigs.k8s.io/descheduler/pkg/api"
 )
 
 const SystemCriticalPriority = 2 * int32(1000000000)
@@ -33,3 +39,36 @@ func PodMatchesTermsNamespaceAndSelector(pod *v1.Pod, namespaces sets.String, se
 	}
 	return true
 }
+
+// GetPriorityFromPriorityClass gets priority from the given priority class.
+// If no priority class is provided, it will return SystemCriticalPriority by default.
+func GetPriorityFromPriorityClass(ctx context.Context, client clientset.Interface, name string) (int32, error) {
+	if name != "" {
+		priorityClass, err := client.SchedulingV1().PriorityClasses().Get(ctx, name, metav1.GetOptions{})
+		if err != nil {
+			return 0, err
+		}
+		return priorityClass.Value, nil
+	}
+	return SystemCriticalPriority, nil
+}
+
+// GetPriorityFromStrategyParams gets priority from the given StrategyParameters.
+// It will return SystemCriticalPriority by default.
+func GetPriorityFromStrategyParams(ctx context.Context, client clientset.Interface, params *api.StrategyParameters) (priority int32, err error) {
+	if params == nil {
+		return SystemCriticalPriority, nil
+	}
+	if params.ThresholdPriority != nil {
+		priority = *params.ThresholdPriority
+	} else {
+		priority, err = GetPriorityFromPriorityClass(ctx, client, params.ThresholdPriorityClassName)
+		if err != nil {
+			return
+		}
+	}
+	if priority > SystemCriticalPriority {
+		return 0, fmt.Errorf("Priority threshold can't be greater than %d", SystemCriticalPriority)
+	}
+	return
+}