Refactor TopologyManager to be more explicit about bestHint calculation

Signed-off-by: Kevin Klues <kklues@nvidia.com>

pkg/kubelet/cm/topologymanager/policy.go

@@ -94,51 +94,60 @@ func filterProvidersHints(providersHints []map[string][]TopologyHint) [][]Topolo
 	return allProviderHints
 }
 
-func mergeFilteredHints(numaNodes []int, filteredHints [][]TopologyHint) TopologyHint {
-	// Set the default affinity as an any-numa affinity containing the list
-	// of NUMA Nodes available on this machine.
-	defaultAffinity, _ := bitmask.NewBitMask(numaNodes...)
+func compareHints(current *TopologyHint, candidate *TopologyHint) *TopologyHint {
+	// Only consider candidates that result in a NUMANodeAffinity > 0 to
+	// replace the current bestHint.
+	if candidate.NUMANodeAffinity.Count() == 0 {
+		return current
+	}
 
-	// Set the bestHint to return from this function as {nil false}.
-	// This will only be returned if no better hint can be found when
-	// merging hints from each hint provider.
-	bestHint := TopologyHint{defaultAffinity, false}
+	// If no current bestHint is set, return the candidate as the bestHint.
+	if current == nil {
+		return candidate
+	}
+
+	// If the current bestHint is non-preferred and the candidate hint is
+	// preferred, always choose the preferred hint over the non-preferred one.
+	if !current.Preferred && candidate.Preferred {
+		return candidate
+	}
+
+	// If the current bestHint is preferred and the candidate hint is
+	// non-preferred, never update the bestHint, regardless of the
+	// candidate hint's narowness.
+	if current.Preferred && !candidate.Preferred {
+		return current
+	}
+
+	// If the current bestHint and the candidate hint have the same
+	// preference, only consider candidate hints that have a narrower
+	// NUMANodeAffinity than the NUMANodeAffinity in the current bestHint.
+	if !candidate.NUMANodeAffinity.IsNarrowerThan(current.NUMANodeAffinity) {
+		return current
+	}
+
+	// In all other cases, update the bestHint to the candidate hint.
+	return candidate
+}
+
+func mergeFilteredHints(numaNodes []int, filteredHints [][]TopologyHint) TopologyHint {
+	var bestHint *TopologyHint
 	iterateAllProviderTopologyHints(filteredHints, func(permutation []TopologyHint) {
 		// Get the NUMANodeAffinity from each hint in the permutation and see if any
 		// of them encode unpreferred allocations.
 		mergedHint := mergePermutation(numaNodes, permutation)
-		// Only consider mergedHints that result in a NUMANodeAffinity > 0 to
-		// replace the current bestHint.
-		if mergedHint.NUMANodeAffinity.Count() == 0 {
-			return
-		}
 
-		// If the current bestHint is non-preferred and the new mergedHint is
-		// preferred, always choose the preferred hint over the non-preferred one.
-		if mergedHint.Preferred && !bestHint.Preferred {
-			bestHint = mergedHint
-			return
-		}
-
-		// If the current bestHint is preferred and the new mergedHint is
-		// non-preferred, never update bestHint, regardless of mergedHint's
-		// narowness.
-		if !mergedHint.Preferred && bestHint.Preferred {
-			return
-		}
-
-		// If mergedHint and bestHint has the same preference, only consider
-		// mergedHints that have a narrower NUMANodeAffinity than the
-		// NUMANodeAffinity in the current bestHint.
-		if !mergedHint.NUMANodeAffinity.IsNarrowerThan(bestHint.NUMANodeAffinity) {
-			return
-		}
-
-		// In all other cases, update bestHint to the current mergedHint
-		bestHint = mergedHint
+		// Compare the current bestHint with the candidate mergedHint and
+		// update bestHint if appropriate.
+		bestHint = compareHints(bestHint, &mergedHint)
 	})
 
-	return bestHint
+	if bestHint == nil {
+		defaultAffinity, _ := bitmask.NewBitMask(numaNodes...)
+		bestHint = &TopologyHint{defaultAffinity, false}
+	}
+
+	return *bestHint
 }
 
 // Iterate over all permutations of hints in 'allProviderHints [][]TopologyHint'.