YARN-7374. Improve performance of DRF comparisons for resource types in fair scheduler

(cherry picked from commit 9711b78998ca3a1f7734058a78c7baddd130ce0f)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-api/src/main/java/org/apache/hadoop/yarn/api/records/Resource.java

@@ -22,6 +22,7 @@ import java.util.Arrays;
 
 import org.apache.commons.lang.NotImplementedException;
 import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceAudience.Private;
 import org.apache.hadoop.classification.InterfaceAudience.Public;
 import org.apache.hadoop.classification.InterfaceStability;
 import org.apache.hadoop.classification.InterfaceStability.Evolving;
@@ -66,8 +67,10 @@ public abstract class Resource implements Comparable<Resource> {
   // copy array, etc.
   protected static final int NUM_MANDATORY_RESOURCES = 2;
 
-  protected static final int MEMORY_INDEX = 0;
-  protected static final int VCORES_INDEX = 1;
+  @Private
+  public static final int MEMORY_INDEX = 0;
+  @Private
+  public static final int VCORES_INDEX = 1;
 
   @Public
   @Stable

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-api/src/main/java/org/apache/hadoop/yarn/api/records/ResourceInformation.java

@@ -18,7 +18,6 @@
 
 package org.apache.hadoop.yarn.api.records;
 
-import org.apache.curator.shaded.com.google.common.reflect.ClassPath;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.yarn.api.protocolrecords.ResourceTypes;
 import org.apache.hadoop.yarn.util.UnitsConversionUtil;

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/policies/DominantResourceFairnessPolicy.java

@@ -47,8 +47,12 @@ public class DominantResourceFairnessPolicy extends SchedulingPolicy {
 
   public static final String NAME = "DRF";
 
-  private static final DominantResourceFairnessComparator COMPARATOR =
-      new DominantResourceFairnessComparator();
+  private static final int NUM_RESOURCES =
+      ResourceUtils.getNumberOfKnownResourceTypes();
+  private static final DominantResourceFairnessComparator COMPARATORN =
+      new DominantResourceFairnessComparatorN();
+  private static final DominantResourceFairnessComparator COMPARATOR2 =
+      new DominantResourceFairnessComparator2();
   private static final DominantResourceCalculator CALCULATOR =
       new DominantResourceCalculator();
 
@@ -59,7 +63,15 @@ public class DominantResourceFairnessPolicy extends SchedulingPolicy {
 
   @Override
   public Comparator<Schedulable> getComparator() {
-    return COMPARATOR;
+    if (NUM_RESOURCES == 2) {
+      // To improve performance, if we know we're dealing with the common
+      // case of only CPU and memory, then handle CPU and memory explicitly.
+      return COMPARATOR2;
+    } else {
+      // Otherwise, do it the generic way.
+      return COMPARATORN;
+    }
+
   }
 
   @Override
@@ -107,25 +119,56 @@ public class DominantResourceFairnessPolicy extends SchedulingPolicy {
 
   @Override
   public void initialize(FSContext fsContext) {
-    COMPARATOR.setFSContext(fsContext);
+    COMPARATORN.setFSContext(fsContext);
+    COMPARATOR2.setFSContext(fsContext);
   }
 
   /**
    * This class compares two {@link Schedulable} instances according to the
    * DRF policy. If neither instance is below min share, approximate fair share
-   * ratios are compared.
+   * ratios are compared. Subclasses of this class will do the actual work of
+   * the comparison, specialized for the number of configured resource types.
    */
-  public static class DominantResourceFairnessComparator
+  public abstract static class DominantResourceFairnessComparator
       implements Comparator<Schedulable> {
-    private FSContext fsContext;
+    protected FSContext fsContext;
 
     public void setFSContext(FSContext fsContext) {
       this.fsContext = fsContext;
     }
 
+    /**
+     * This method is used when apps are tied in fairness ratio. It breaks
+     * the tie by submit time and job name to get a deterministic ordering,
+     * which is useful for unit tests.
+     *
+     * @param s1 the first item to compare
+     * @param s2 the second item to compare
+     * @return &lt; 0, 0, or &gt; 0 if the first item is less than, equal to,
+     * or greater than the second item, respectively
+     */
+    protected int compareAttribrutes(Schedulable s1, Schedulable s2) {
+      int res = (int) Math.signum(s1.getStartTime() - s2.getStartTime());
+
+      if (res == 0) {
+        res = s1.getName().compareTo(s2.getName());
+      }
+
+      return res;
+    }
+  }
+
+  /**
+   * This class compares two {@link Schedulable} instances according to the
+   * DRF policy. If neither instance is below min share, approximate fair share
+   * ratios are compared. This class makes no assumptions about the number of
+   * resource types.
+   */
+  @VisibleForTesting
+  static class DominantResourceFairnessComparatorN
+      extends DominantResourceFairnessComparator {
     @Override
     public int compare(Schedulable s1, Schedulable s2) {
-      ResourceInformation[] info = ResourceUtils.getResourceTypesArray();
       Resource usage1 = s1.getResourceUsage();
       Resource usage2 = s2.getResourceUsage();
       Resource minShare1 = s1.getMinShare();
@@ -135,8 +178,8 @@ public class DominantResourceFairnessPolicy extends SchedulingPolicy {
       // These arrays hold the usage, fair, and min share ratios for each
       // resource type. ratios[0][x] are the usage ratios, ratios[1][x] are
       // the fair share ratios, and ratios[2][x] are the min share ratios.
-      float[][] ratios1 = new float[info.length][3];
-      float[][] ratios2 = new float[info.length][3];
+      float[][] ratios1 = new float[NUM_RESOURCES][3];
+      float[][] ratios2 = new float[NUM_RESOURCES][3];
 
       // Calculate cluster shares and approximate fair shares for each
       // resource type of both schedulables.
@@ -155,7 +198,7 @@ public class DominantResourceFairnessPolicy extends SchedulingPolicy {
           usage2.getResources()[dominant2].getValue() <
           minShare2.getResources()[dominant2].getValue();
       
-      int res = 0;
+      int res;
 
       if (!s2Needy && !s1Needy) {
         // Sort shares by usage ratio and compare them by approximate fair share
@@ -176,13 +219,7 @@ public class DominantResourceFairnessPolicy extends SchedulingPolicy {
       }
 
       if (res == 0) {
-        // Apps are tied in fairness ratio. Break the tie by submit time and job
-        // name to get a deterministic ordering, which is useful for unit tests.
-        res = (int) Math.signum(s1.getStartTime() - s2.getStartTime());
-
-        if (res == 0) {
-          res = s1.getName().compareTo(s2.getName());
-        }
+        res = compareAttribrutes(s1, s2);
       }
 
       return res;
@@ -206,7 +243,7 @@ public class DominantResourceFairnessPolicy extends SchedulingPolicy {
 
     /**
      * Calculate a resource's usage ratio and approximate fair share ratio.
-     * The {@code shares} array will be populated with both the usage ratio
+     * The {@code ratios} array will be populated with both the usage ratio
      * and the approximate fair share ratio for each resource type. The usage
      * ratio is calculated as {@code resource} divided by {@code cluster}.
      * The approximate fair share ratio is calculated as the usage ratio
@@ -221,18 +258,18 @@ public class DominantResourceFairnessPolicy extends SchedulingPolicy {
      * because when comparing resources, the resource with the higher weight
      * will be assigned by the scheduler a proportionally higher fair share.
      *
-     * The {@code shares} array must be at least <i>n</i> x 2, where <i>n</i>
+     * The {@code ratios} array must be at least <i>n</i> x 2, where <i>n</i>
      * is the number of resource types. Only the first and second indices of
-     * the inner arrays in the {@code shares} array will be used, e.g.
-     * {@code shares[x][0]} and {@code shares[x][1]}.
+     * the inner arrays in the {@code ratios} array will be used, e.g.
+     * {@code ratios[x][0]} and {@code ratios[x][1]}.
      *
      * The return value will be the index of the dominant resource type in the
-     * {@code shares} array. The dominant resource is the resource type for
+     * {@code ratios} array. The dominant resource is the resource type for
      * which {@code resource} has the largest usage ratio.
      *
      * @param resource the resource for which to calculate ratios
      * @param cluster the total cluster resources
-     * @param ratios the shares array to populate
+     * @param ratios the share ratios array to populate
      * @param weight the resource weight
      * @return the index of the resource type with the largest cluster share
      */
@@ -275,7 +312,7 @@ public class DominantResourceFairnessPolicy extends SchedulingPolicy {
      *
      * @param resource the resource for which to calculate min shares
      * @param minShare the min share
-     * @param ratios the shares array to populate
+     * @param ratios the share ratios array to populate
      */
     @VisibleForTesting
     void calculateMinShareRatios(Resource resource, Resource minShare,
@@ -320,4 +357,155 @@ public class DominantResourceFairnessPolicy extends SchedulingPolicy {
       return ret;
     }
   }
+
+  /**
+   * This class compares two {@link Schedulable} instances according to the
+   * DRF policy in the special case that only CPU and memory are configured.
+   * If neither instance is below min share, approximate fair share
+   * ratios are compared.
+   */
+  @VisibleForTesting
+  static class DominantResourceFairnessComparator2
+      extends DominantResourceFairnessComparator {
+    @Override
+    public int compare(Schedulable s1, Schedulable s2) {
+      ResourceInformation[] resourceInfo1 =
+          s1.getResourceUsage().getResources();
+      ResourceInformation[] resourceInfo2 =
+          s2.getResourceUsage().getResources();
+      ResourceInformation[] minShareInfo1 = s1.getMinShare().getResources();
+      ResourceInformation[] minShareInfo2 = s2.getMinShare().getResources();
+      ResourceInformation[] clusterInfo =
+          fsContext.getClusterResource().getResources();
+      double[] shares1 = new double[2];
+      double[] shares2 = new double[2];
+
+      int dominant1 = calculateClusterAndFairRatios(resourceInfo1,
+          s1.getWeight(), clusterInfo, shares1);
+      int dominant2 = calculateClusterAndFairRatios(resourceInfo2,
+          s2.getWeight(), clusterInfo, shares2);
+
+      // A queue is needy for its min share if its dominant resource
+      // (with respect to the cluster capacity) is below its configured min
+      // share for that resource
+      boolean s1Needy = resourceInfo1[dominant1].getValue() <
+          minShareInfo1[dominant1].getValue();
+      boolean s2Needy = resourceInfo1[dominant2].getValue() <
+          minShareInfo2[dominant2].getValue();
+
+      int res;
+
+      if (!s2Needy && !s1Needy) {
+        res = (int) Math.signum(shares1[dominant1] - shares2[dominant2]);
+
+        if (res == 0) {
+          // Because memory and CPU are indices 0 and 1, we can find the
+          // non-dominant index by subtracting the dominant index from 1.
+          res = (int) Math.signum(shares1[1 - dominant1] -
+              shares2[1 - dominant2]);
+        }
+      } else if (s1Needy && !s2Needy) {
+        res = -1;
+      } else if (s2Needy && !s1Needy) {
+        res = 1;
+      } else {
+        double[] minShares1 =
+            calculateMinShareRatios(resourceInfo1, minShareInfo1);
+        double[] minShares2 =
+            calculateMinShareRatios(resourceInfo2, minShareInfo2);
+
+        res = (int) Math.signum(minShares1[dominant1] - minShares2[dominant2]);
+
+        if (res == 0) {
+          res = (int) Math.signum(minShares1[1 - dominant1] -
+              minShares2[1 - dominant2]);
+        }
+      }
+
+      if (res == 0) {
+        res = compareAttribrutes(s1, s2);
+      }
+
+      return res;
+    }
+
+    /**
+     * Calculate a resource's usage ratio and approximate fair share ratio
+     * assuming that CPU and memory are the only configured resource types.
+     * The {@code shares} array will be populated with the approximate fair
+     * share ratio for each resource type. The approximate fair share ratio
+     * is calculated as {@code resourceInfo} divided by {@code cluster} and
+     * the {@code weight}. If the cluster's resources are 100MB and
+     * 10 vcores, the usage ({@code resourceInfo}) is 10 MB and 5 CPU, and the
+     * weights are 2, the fair share ratios will be 0.05 and 0.25.
+     *
+     * The approximate fair share ratio is the usage divided by the
+     * approximate fair share, i.e. the cluster resources times the weight.
+     * The approximate fair share is an acceptable proxy for the fair share
+     * because when comparing resources, the resource with the higher weight
+     * will be assigned by the scheduler a proportionally higher fair share.
+     *
+     * The length of the {@code shares} array must be at least 2.
+     *
+     * The return value will be the index of the dominant resource type in the
+     * {@code shares} array. The dominant resource is the resource type for
+     * which {@code resourceInfo} has the largest usage ratio.
+     *
+     * @param resourceInfo the resource for which to calculate ratios
+     * @param weight the resource weight
+     * @param clusterInfo the total cluster resources
+     * @param shares the share ratios array to populate
+     * @return the index of the resource type with the largest cluster share
+     */
+    @VisibleForTesting
+    int calculateClusterAndFairRatios(ResourceInformation[] resourceInfo,
+        float weight, ResourceInformation[] clusterInfo, double[] shares) {
+      int dominant;
+
+      shares[Resource.MEMORY_INDEX] =
+          ((double) resourceInfo[Resource.MEMORY_INDEX].getValue()) /
+          clusterInfo[Resource.MEMORY_INDEX].getValue();
+      shares[Resource.VCORES_INDEX] =
+          ((double) resourceInfo[Resource.VCORES_INDEX].getValue()) /
+          clusterInfo[Resource.VCORES_INDEX].getValue();
+      dominant =
+          shares[Resource.VCORES_INDEX] > shares[Resource.MEMORY_INDEX] ?
+          Resource.VCORES_INDEX : Resource.MEMORY_INDEX;
+
+      shares[Resource.MEMORY_INDEX] /= weight;
+      shares[Resource.VCORES_INDEX] /= weight;
+
+      return dominant;
+    }
+
+    /**
+     * Calculate a resource's min share ratios assuming that CPU and memory
+     * are the only configured resource types. The return array will be
+     * populated with the {@code resourceInfo} divided by {@code minShareInfo}
+     * for each resource type. If the min shares are 5 MB and 10 vcores, and
+     * the usage ({@code resourceInfo}) is 10 MB and 5 CPU, the ratios will
+     * be 2 and 0.5.
+     *
+     * The length of the {@code ratios} array must be 2.
+     *
+     * @param resourceInfo the resource for which to calculate min shares
+     * @param minShareInfo the min share
+     * @return the share ratios
+     */
+    @VisibleForTesting
+    double[] calculateMinShareRatios(ResourceInformation[] resourceInfo,
+        ResourceInformation[] minShareInfo) {
+      double[] minShares1 = new double[2];
+
+      // both are needy below min share
+      minShares1[Resource.MEMORY_INDEX] =
+          ((double) resourceInfo[Resource.MEMORY_INDEX].getValue()) /
+          minShareInfo[Resource.MEMORY_INDEX].getValue();
+      minShares1[Resource.VCORES_INDEX] =
+          ((double) resourceInfo[Resource.VCORES_INDEX].getValue()) /
+          minShareInfo[Resource.VCORES_INDEX].getValue();
+
+      return minShares1;
+    }
+  }
 }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/policies/TestDominantResourceFairnessPolicy.java

@@ -24,21 +24,22 @@ import static org.mockito.Mockito.when;
 
 import java.util.Comparator;
 import java.util.Map;
+
 import org.apache.curator.shaded.com.google.common.base.Joiner;
 import org.apache.hadoop.conf.Configuration;
-
 import org.apache.hadoop.yarn.api.records.Resource;
 import org.apache.hadoop.yarn.api.records.ResourceInformation;
 import org.apache.hadoop.yarn.conf.YarnConfiguration;
 import org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.FSContext;
 import org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.FakeSchedulable;
 import org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.Schedulable;
-import org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.policies.DominantResourceFairnessPolicy.DominantResourceFairnessComparator;
+import org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.policies.DominantResourceFairnessPolicy.DominantResourceFairnessComparatorN;
+import org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.policies.DominantResourceFairnessPolicy.DominantResourceFairnessComparator2;
 import org.apache.hadoop.yarn.server.utils.BuilderUtils;
 import org.apache.hadoop.yarn.util.resource.ResourceUtils;
 import org.apache.hadoop.yarn.util.resource.Resources;
 import org.junit.Assert;
-import org.junit.BeforeClass;
+import org.junit.Before;
 import org.junit.Test;
 
 /**
@@ -46,8 +47,8 @@ import org.junit.Test;
  * container before sched2
  */
 public class TestDominantResourceFairnessPolicy {
-  @BeforeClass
-  public static void setup() {
+  @Before
+  public void setup() {
     addResources("test");
   }
 
@@ -77,7 +78,6 @@ public class TestDominantResourceFairnessPolicy {
     return createSchedulable(memUsage, cpuUsage, weights, 0, 0);
   }
 
-  
   private Schedulable createSchedulable(int memUsage, int cpuUsage,
       float weights, int minMemShare, int minCpuShare) {
     Resource usage = BuilderUtils.newResource(memUsage, cpuUsage);
@@ -97,6 +97,12 @@ public class TestDominantResourceFairnessPolicy {
         c.compare(s1, s2) < 0);
   }
   
+  @Test
+  public void testSameDominantResource2() {
+    ResourceUtils.resetResourceTypes(new Configuration());
+    testSameDominantResource();
+  }
+
   @Test
   public void testDifferentDominantResource() {
     Comparator c = createComparator(8000, 8);
@@ -107,6 +113,12 @@ public class TestDominantResourceFairnessPolicy {
         c.compare(s1, s2) < 0);
   }
   
+  @Test
+  public void testDifferentDominantResource2() {
+    ResourceUtils.resetResourceTypes(new Configuration());
+    testDifferentDominantResource();
+  }
+
   @Test
   public void testOneIsNeedy() {
     Comparator c = createComparator(8000, 8);
@@ -117,6 +129,12 @@ public class TestDominantResourceFairnessPolicy {
         c.compare(s1, s2) < 0);
   }
   
+  @Test
+  public void testOneIsNeedy2() {
+    ResourceUtils.resetResourceTypes(new Configuration());
+    testOneIsNeedy();
+  }
+
   @Test
   public void testBothAreNeedy() {
     Comparator c = createComparator(8000, 100);
@@ -137,6 +155,12 @@ public class TestDominantResourceFairnessPolicy {
         c.compare(s1, s2) < 0);
   }
   
+  @Test
+  public void testBothAreNeedy2() {
+    ResourceUtils.resetResourceTypes(new Configuration());
+    testBothAreNeedy();
+  }
+
   @Test
   public void testEvenWeightsSameDominantResource() {
     assertTrue(createComparator(8000, 8).compare(
@@ -147,6 +171,12 @@ public class TestDominantResourceFairnessPolicy {
         createSchedulable(1000, 2)) < 0);
   }
   
+  @Test
+  public void testEvenWeightsSameDominantResource2() {
+    ResourceUtils.resetResourceTypes(new Configuration());
+    testEvenWeightsSameDominantResource();
+  }
+
   @Test
   public void testEvenWeightsDifferentDominantResource() {
     assertTrue(createComparator(8000, 8).compare(
@@ -157,14 +187,20 @@ public class TestDominantResourceFairnessPolicy {
         createSchedulable(1000, 2)) < 0);
   }
   
+  @Test
+  public void testEvenWeightsDifferentDominantResource2() {
+    ResourceUtils.resetResourceTypes(new Configuration());
+    testEvenWeightsDifferentDominantResource();
+  }
+
   @Test
   public void testSortShares() {
     float[][] ratios1 = {{0.3f, 2.0f}, {0.2f, 1.0f}, {0.4f, 0.1f}};
     float[][] ratios2 = {{0.2f, 9.0f}, {0.3f, 2.0f}, {0.25f, 0.1f}};
     float[][] expected1 = {{0.4f, 0.1f}, {0.3f, 2.0f}, {0.2f, 1.0f}};
     float[][] expected2 = {{0.3f, 2.0f}, {0.25f, 0.1f}, {0.2f, 9.0f}};
-    DominantResourceFairnessComparator comparator =
-        new DominantResourceFairnessComparator();
+    DominantResourceFairnessComparatorN comparator =
+        new DominantResourceFairnessComparatorN();
 
     comparator.sortRatios(ratios1, ratios2);
 
@@ -184,8 +220,8 @@ public class TestDominantResourceFairnessPolicy {
     Resource used = Resources.createResource(10, 5);
     Resource capacity = Resources.createResource(100, 10);
     float[][] shares = new float[3][2];
-    DominantResourceFairnessComparator comparator =
-        new DominantResourceFairnessComparator();
+    DominantResourceFairnessComparatorN comparator =
+        new DominantResourceFairnessComparatorN();
 
     used.setResourceValue("test", 2L);
     capacity.setResourceValue("test", 5L);
@@ -206,14 +242,34 @@ public class TestDominantResourceFairnessPolicy {
         dominant);
   }
 
+  @Test
+  public void testCalculateClusterAndFairRatios2() {
+    ResourceUtils.resetResourceTypes(new Configuration());
+    Resource used = Resources.createResource(10, 5);
+    Resource capacity = Resources.createResource(100, 10);
+    double[] shares = new double[2];
+    DominantResourceFairnessComparator2 comparator =
+        new DominantResourceFairnessComparator2();
+    int dominant =
+        comparator.calculateClusterAndFairRatios(used.getResources(), 1.0f,
+            capacity.getResources(), shares);
+
+    assertEquals("Calculated usage ratio for memory (10MB out of 100MB) is "
+        + "incorrect", 0.1, shares[Resource.MEMORY_INDEX], .00001);
+    assertEquals("Calculated usage ratio for vcores (5 out of 10) is "
+        + "incorrect", 0.5, shares[Resource.VCORES_INDEX], .00001);
+    assertEquals("The wrong dominant resource index was returned",
+        Resource.VCORES_INDEX, dominant);
+  }
+
   @Test
   public void testCalculateMinShareRatios() {
     Map<String, Integer> index = ResourceUtils.getResourceTypeIndex();
     Resource used = Resources.createResource(10, 5);
     Resource minShares = Resources.createResource(5, 10);
     float[][] ratios = new float[3][3];
-    DominantResourceFairnessComparator comparator =
-        new DominantResourceFairnessComparator();
+    DominantResourceFairnessComparatorN comparator =
+        new DominantResourceFairnessComparatorN();
 
     used.setResourceValue("test", 2L);
     minShares.setResourceValue("test", 0L);
@@ -231,6 +287,24 @@ public class TestDominantResourceFairnessPolicy {
         0.00001f);
   }
 
+  @Test
+  public void testCalculateMinShareRatios2() {
+    ResourceUtils.resetResourceTypes(new Configuration());
+    Resource used = Resources.createResource(10, 5);
+    Resource minShares = Resources.createResource(5, 10);
+    DominantResourceFairnessComparator2 comparator =
+        new DominantResourceFairnessComparator2();
+
+    double[] ratios =
+        comparator.calculateMinShareRatios(used.getResources(),
+            minShares.getResources());
+
+    assertEquals("Calculated min share ratio for memory (10MB out of 5MB) is "
+        + "incorrect", 2.0, ratios[Resource.MEMORY_INDEX], .00001f);
+    assertEquals("Calculated min share ratio for vcores (5 out of 10) is "
+        + "incorrect", 0.5, ratios[Resource.VCORES_INDEX], .00001f);
+  }
+
   @Test
   public void testCompareShares() {
     float[][] ratios1 = {
@@ -248,8 +322,8 @@ public class TestDominantResourceFairnessPolicy {
         {0.2f, 0.1f, 2.0f},
         {0.1f, 2.0f, 1.0f}
     };
-    DominantResourceFairnessComparator comparator =
-        new DominantResourceFairnessComparator();
+    DominantResourceFairnessComparatorN comparator =
+        new DominantResourceFairnessComparatorN();
 
     int ret = comparator.compareRatios(ratios1, ratios2, 0);