DRA CEL: log actual cost

This may be useful for validating the cost estimate.

Author: pohly

staging/src/k8s.io/dynamic-resource-allocation/cel/compile.go

@@ -198,14 +198,14 @@ func getAttributeValue(attr resourceapi.DeviceAttribute) (any, error) {
 
 var boolType = reflect.TypeOf(true)
 
-func (c CompilationResult) DeviceMatches(ctx context.Context, input Device) (bool, error) {
+func (c CompilationResult) DeviceMatches(ctx context.Context, input Device) (bool, *cel.EvalDetails, error) {
 	// TODO (future): avoid building these maps and instead use a proxy
 	// which wraps the underlying maps and directly looks up values.
 	attributes := make(map[string]any)
 	for name, attr := range input.Attributes {
 		value, err := getAttributeValue(attr)
 		if err != nil {
-			return false, fmt.Errorf("attribute %s: %w", name, err)
+			return false, nil, fmt.Errorf("attribute %s: %w", name, err)
 		}
 		domain, id := parseQualifiedName(name, input.Driver)
 		if attributes[domain] == nil {
@@ -231,19 +231,19 @@ func (c CompilationResult) DeviceMatches(ctx context.Context, input Device) (boo
 		},
 	}
 
-	result, _, err := c.Program.ContextEval(ctx, variables)
+	result, details, err := c.Program.ContextEval(ctx, variables)
 	if err != nil {
-		return false, err
+		return false, details, err
 	}
 	resultAny, err := result.ConvertToNative(boolType)
 	if err != nil {
-		return false, fmt.Errorf("CEL result of type %s could not be converted to bool: %w", result.Type().TypeName(), err)
+		return false, details, fmt.Errorf("CEL result of type %s could not be converted to bool: %w", result.Type().TypeName(), err)
 	}
 	resultBool, ok := resultAny.(bool)
 	if !ok {
-		return false, fmt.Errorf("CEL native result value should have been a bool, got instead: %T", resultAny)
+		return false, details, fmt.Errorf("CEL native result value should have been a bool, got instead: %T", resultAny)
 	}
-	return resultBool, nil
+	return resultBool, details, nil
 }
 
 func mustBuildEnv() *environment.EnvSet {

staging/src/k8s.io/dynamic-resource-allocation/cel/compile_test.go

@@ -254,7 +254,18 @@ device.attributes["dra.example.com"]["version"].isGreaterThan(semver("0.0.1"))
 				t.Errorf("expected CEL cost %d, got %d instead", expect, actual)
 			}
 
-			match, err := result.DeviceMatches(ctx, Device{Attributes: scenario.attributes, Capacity: scenario.capacity, Driver: scenario.driver})
+			match, details, err := result.DeviceMatches(ctx, Device{Attributes: scenario.attributes, Capacity: scenario.capacity, Driver: scenario.driver})
+			// details.ActualCost can be called for nil details, no need to check.
+			actualCost := ptr.Deref(details.ActualCost(), 0)
+			if scenario.expectCost > 0 {
+				t.Logf("actual cost %d, %d%% of worst-case estimate", actualCost, actualCost*100/scenario.expectCost)
+			} else {
+				t.Logf("actual cost %d, expected zero costs", actualCost)
+				if actualCost > 0 {
+					t.Errorf("expected zero costs for (presumably) constant expression %q, got instead %d", scenario.expression, actualCost)
+				}
+			}
+
 			if err != nil {
 				if scenario.expectMatchError == "" {
 					t.Fatalf("unexpected evaluation error: %v", err)

staging/src/k8s.io/dynamic-resource-allocation/structured/allocator.go

@@ -30,6 +30,7 @@ import (
 	resourcelisters "k8s.io/client-go/listers/resource/v1alpha3"
 	"k8s.io/dynamic-resource-allocation/cel"
 	"k8s.io/klog/v2"
+	"k8s.io/utils/ptr"
 )
 
 // ClaimLister returns a subset of the claims that a
@@ -665,11 +666,11 @@ func (alloc *allocator) selectorsMatch(r requestIndices, device *resourceapi.Bas
 			return false, fmt.Errorf("claim %s: selector #%d: CEL compile error: %w", klog.KObj(alloc.claimsToAllocate[r.claimIndex]), i, expr.Error)
 		}
 
-		matches, err := expr.DeviceMatches(alloc.ctx, cel.Device{Driver: deviceID.Driver, Attributes: device.Attributes, Capacity: device.Capacity})
+		matches, details, err := expr.DeviceMatches(alloc.ctx, cel.Device{Driver: deviceID.Driver, Attributes: device.Attributes, Capacity: device.Capacity})
 		if class != nil {
-			alloc.logger.V(7).Info("CEL result", "device", deviceID, "class", klog.KObj(class), "selector", i, "expression", selector.CEL.Expression, "matches", matches, "err", err)
+			alloc.logger.V(7).Info("CEL result", "device", deviceID, "class", klog.KObj(class), "selector", i, "expression", selector.CEL.Expression, "matches", matches, "actualCost", ptr.Deref(details.ActualCost(), 0), "err", err)
 		} else {
-			alloc.logger.V(7).Info("CEL result", "device", deviceID, "claim", klog.KObj(alloc.claimsToAllocate[r.claimIndex]), "selector", i, "expression", selector.CEL.Expression, "matches", matches, "err", err)
+			alloc.logger.V(7).Info("CEL result", "device", deviceID, "claim", klog.KObj(alloc.claimsToAllocate[r.claimIndex]), "selector", i, "expression", selector.CEL.Expression, "actualCost", ptr.Deref(details.ActualCost(), 0), "matches", matches, "err", err)
 		}
 
 		if err != nil {