diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/LightWeightCache.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/LightWeightCache.java
index a0a553af103..d79aade3158 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/LightWeightCache.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/LightWeightCache.java
@@ -76,14 +76,6 @@ public class LightWeightCache<K, E extends K> extends LightWeightGSet<K, E> {
       return l > r? 1: l < r? -1: 0;
     }
   };
-
-  /** A clock for measuring time so that it can be mocked in unit tests. */
-  static class Clock {
-    /** @return the current time. */
-    long currentTime() {
-      return System.nanoTime();
-    }
-  }
   
   private static int updateRecommendedLength(int recommendedLength,
       int sizeLimit) {
@@ -102,7 +94,7 @@ public class LightWeightCache<K, E extends K> extends LightWeightGSet<K, E> {
   private final long creationExpirationPeriod;
   private final long accessExpirationPeriod;
   private final int sizeLimit;
-  private final Clock clock;
+  private final Timer timer;
 
   /**
    * @param recommendedLength Recommended size of the internal array.
@@ -120,7 +112,7 @@ public class LightWeightCache<K, E extends K> extends LightWeightGSet<K, E> {
       final long creationExpirationPeriod,
       final long accessExpirationPeriod) {
     this(recommendedLength, sizeLimit,
-        creationExpirationPeriod, accessExpirationPeriod, new Clock());
+        creationExpirationPeriod, accessExpirationPeriod, new Timer());
   }
 
   @VisibleForTesting
@@ -128,7 +120,7 @@ public class LightWeightCache<K, E extends K> extends LightWeightGSet<K, E> {
       final int sizeLimit,
       final long creationExpirationPeriod,
       final long accessExpirationPeriod,
-      final Clock clock) {
+      final Timer timer) {
     super(updateRecommendedLength(recommendedLength, sizeLimit));
 
     this.sizeLimit = sizeLimit;
@@ -147,11 +139,11 @@ public class LightWeightCache<K, E extends K> extends LightWeightGSet<K, E> {
 
     this.queue = new PriorityQueue<Entry>(
         sizeLimit > 0? sizeLimit + 1: 1 << 10, expirationTimeComparator);
-    this.clock = clock;
+    this.timer = timer;
   }
 
   void setExpirationTime(final Entry e, final long expirationPeriod) {
-    e.setExpirationTime(clock.currentTime() + expirationPeriod);
+    e.setExpirationTime(timer.monotonicNowNanos() + expirationPeriod);
   }
 
   boolean isExpired(final Entry e, final long now) {
@@ -168,7 +160,7 @@ public class LightWeightCache<K, E extends K> extends LightWeightGSet<K, E> {
 
   /** Evict expired entries. */
   private void evictExpiredEntries() {
-    final long now = clock.currentTime();
+    final long now = timer.monotonicNowNanos();
     for(int i = 0; i < EVICTION_LIMIT; i++) {
       final Entry peeked = queue.peek();
       if (peeked == null || !isExpired(peeked, now)) {
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/Time.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/Time.java
index e96fa77dbd7..db5a56730d0 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/Time.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/Time.java
@@ -65,6 +65,16 @@ public final class Time {
     return System.nanoTime() / NANOSECONDS_PER_MILLISECOND;
   }
 
+  /**
+   * Same as {@link #monotonicNow()} but returns its result in nanoseconds.
+   * Note that this is subject to the same resolution constraints as
+   * {@link System#nanoTime()}.
+   * @return a monotonic clock that counts in nanoseconds.
+   */
+  public static long monotonicNowNanos() {
+    return System.nanoTime();
+  }
+
   /**
    * Convert time in millisecond to human readable format.
    * @return a human readable string for the input time
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/Timer.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/Timer.java
index e1e21a72200..3165a9b5bf8 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/Timer.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/Timer.java
@@ -48,4 +48,14 @@ public class Timer {
    * @return a monotonic clock that counts in milliseconds.
    */
   public long monotonicNow() { return Time.monotonicNow(); }
+
+  /**
+   * Same as {@link #monotonicNow()} but returns its result in nanoseconds.
+   * Note that this is subject to the same resolution constraints as
+   * {@link System#nanoTime()}.
+   * @return a monotonic clock that counts in nanoseconds.
+   */
+  public long monotonicNowNanos() {
+    return Time.monotonicNowNanos();
+  }
 }
diff --git a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/util/FakeTimer.java b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/util/FakeTimer.java
index 66386fd2b2c..2b5f85075cf 100644
--- a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/util/FakeTimer.java
+++ b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/util/FakeTimer.java
@@ -18,6 +18,7 @@
 
 package org.apache.hadoop.util;
 
+import java.util.concurrent.TimeUnit;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
 
@@ -28,25 +29,38 @@ import org.apache.hadoop.classification.InterfaceStability;
 @InterfaceAudience.Private
 @InterfaceStability.Unstable
 public class FakeTimer extends Timer {
-  private long nowMillis;
+  private long nowNanos;
 
   /** Constructs a FakeTimer with a non-zero value */
   public FakeTimer() {
-    nowMillis = 1000;  // Initialize with a non-trivial value.
+    nowNanos = 1000;  // Initialize with a non-trivial value.
   }
 
   @Override
   public long now() {
-    return nowMillis;
+    return TimeUnit.NANOSECONDS.toMillis(nowNanos);
   }
 
   @Override
   public long monotonicNow() {
-    return nowMillis;
+    return TimeUnit.NANOSECONDS.toMillis(nowNanos);
+  }
+
+  @Override
+  public long monotonicNowNanos() {
+    return nowNanos;
   }
 
   /** Increases the time by milliseconds */
   public void advance(long advMillis) {
-    nowMillis += advMillis;
+    nowNanos += TimeUnit.MILLISECONDS.toNanos(advMillis);
+  }
+
+  /**
+   * Increases the time by nanoseconds.
+   * @param advNanos Nanoseconds to advance by.
+   */
+  public void advanceNanos(long advNanos) {
+    nowNanos += advNanos;
   }
 }
diff --git a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/util/TestLightWeightCache.java b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/util/TestLightWeightCache.java
index dff6937317a..de6181810db 100644
--- a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/util/TestLightWeightCache.java
+++ b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/util/TestLightWeightCache.java
@@ -213,7 +213,7 @@ public class TestLightWeightCache {
     int iterate_count = 0;
     int contain_count = 0;
 
-    private long currentTestTime = ran.nextInt();
+    private FakeTimer fakeTimer = new FakeTimer();
 
     LightWeightCacheTestCase(int tablelength, int sizeLimit,
         long creationExpirationPeriod, long accessExpirationPeriod,
@@ -230,12 +230,7 @@ public class TestLightWeightCache {
 
       data = new IntData(datasize, modulus);
       cache = new LightWeightCache<IntEntry, IntEntry>(tablelength, sizeLimit,
-          creationExpirationPeriod, 0, new LightWeightCache.Clock() {
-        @Override
-        long currentTime() {
-          return currentTestTime;
-        }
-      });
+          creationExpirationPeriod, 0, fakeTimer);
 
       Assert.assertEquals(0, cache.size());
     }
@@ -247,7 +242,7 @@ public class TestLightWeightCache {
       } else {
         final IntEntry h = hashMap.remove(key);
         if (h != null) {
-          Assert.assertTrue(cache.isExpired(h, currentTestTime));
+          Assert.assertTrue(cache.isExpired(h, fakeTimer.monotonicNowNanos()));
         }
       }
       return c;
@@ -266,7 +261,7 @@ public class TestLightWeightCache {
       } else {
         final IntEntry h = hashMap.remove(key);
         if (h != null) {
-          Assert.assertTrue(cache.isExpired(h, currentTestTime));
+          Assert.assertTrue(cache.isExpired(h, fakeTimer.monotonicNowNanos()));
         }
       }
       return c;
@@ -286,7 +281,7 @@ public class TestLightWeightCache {
         final IntEntry h = hashMap.put(entry);
         if (h != null && h != entry) {
           // if h == entry, its expiration time is already updated
-          Assert.assertTrue(cache.isExpired(h, currentTestTime));
+          Assert.assertTrue(cache.isExpired(h, fakeTimer.monotonicNowNanos()));
         }
       }
       return c;
@@ -305,7 +300,7 @@ public class TestLightWeightCache {
       } else {
         final IntEntry h = hashMap.remove(key);
         if (h != null) {
-          Assert.assertTrue(cache.isExpired(h, currentTestTime));
+          Assert.assertTrue(cache.isExpired(h, fakeTimer.monotonicNowNanos()));
         }
       }
       return c;
@@ -339,7 +334,7 @@ public class TestLightWeightCache {
     }
 
     void check() {
-      currentTestTime += ran.nextInt() & 0x3;
+      fakeTimer.advanceNanos(ran.nextInt() & 0x3);
 
       //test size
       sizeTest();